EO Topics - 2017 to 2016
EO-Topics2 (Time frame: 2017-2016)
Large Snow Accumulation in the Alaska Range Linked to Tropical Ocean Warming
December 19, 2017: Snowfall on a major summit in North America's highest mountain range has more than doubled since the beginning of the Industrial Age, according to a study from Dartmouth College, the University of Maine, and the University of New Hampshire. The research not only finds a dramatic increase in snowfall, it further explains connections in the global climate system by attributing the record accumulation to warmer waters thousands of miles away in the tropical Pacific and Indian Oceans. 1)
The study demonstrates that modern snowfall in the iconic Alaska Range is unprecedented for at least the past 1200 years and far exceeds normal variability. "We were shocked when we first saw how much snowfall has increased," said Erich Osterberg, an assistant professor of Earth sciences at Dartmouth College and principal investigator for the research. "We had to check and double-check our results to make sure of the findings. Dramatic increases in temperature and air pollution in modern times have been well established in science, but now we're also seeing dramatic increases in regional precipitation with climate change."
According to the research, wintertime snowfall has increased 117 percent since the mid-19th century in southcentral Alaska in the United States. Summer snows also showed a significant increase of 49 percent in the short period ranging less than two hundred years.
The research, appearing in Scientific Reports, is based on analysis of two ice cores (each 208 m long) collected from the Mount Hunter summit plateau (62°56'N, 151°5'W, 3900 m) in Denali National Park, Alaska. A high snow accumulation rate (1.15 m water equivalent [w. e.] average since 1900) and infrequent surface melt (<0.5% of the core is composed of refrozen melt layers and lenses) at the Mt. Hunter drill site preserve robust seasonal oscillations of several chemical parameters (Na, Ca, Mg, NH4 +, MSA (methanesulfonic acid), δ18O, liquid conductivity, dust concentration), facilitating annual layer counting back to 800 CE (Common Era, Figure 1). — According to the authors, accumulation records in the separate samples taken from just below the summit of the mountain known as "Denali's Child" are in nearly complete agreement. 2)
The annually resolved Denali snow accumulation record (Figure 2) indicates that the post-1950 precipitation increase in the Alaskan weather station records began well before the 20th century, in circa 1840 CE.
"It is now glaringly clear from our ice core record that modern snowfall rates in Alaska are much higher than natural rates before the Industrial Revolution," said Dominic Winski, a research assistant at Dartmouth and the lead author of the report. "This increase in precipitation is also apparent in weather station data from the past 50 years, but ice cores show the scale of the change well above natural conditions."
Once the researchers established snowfall rates, they set out to identify why precipitation has increased so rapidly in such a short amount of time. Scientific models predict as much as a 2 percent increase in global precipitation per degree of warming because warmer air holds more moisture, but this could not account for most of the dramatic increases in Denali snowfall over the studied period.
The research suggests that warming tropical oceans have caused a strengthening of the Aleutian Low pressure system with its northward flow of warm, moist air, driving most of the snowfall increases. Previous research has linked the warming tropical ocean temperatures to higher greenhouse gas concentrations.
The analysis includes a series of dramatic graphs that demonstrate extreme shifts in precipitation and reinforce the global climate connections that link snowfall in the high reaches of the North American continent with warm tropical waters. As noted in the paper (Ref. 2), this same atmospheric connection accounts for a decrease in Hawaiian precipitation.
"Everywhere we look in the North Pacific, we're seeing this same fingerprint from warming tropical oceans. One result is that wintertime climate in the North Pacific is very different than it was 200 years ago. This doesn't just affect Alaska, but Hawaii and the entire Pacific Northwest are impacted as well," said Winski.
The research builds on a recent study using the same ice cores that showed that an intensification of winter storm activity in Alaska and Northwestern Canada, driven by the strengthening Aleutian Low, started in 1740 and is unprecedented in magnitude and duration over the past millennium. The new record shows the result of that increase in Aleutian Low storm activity on snow accumulation.
For this analysis, researchers were able to segment the ice core records by seasons and years using markers like magnesium from spring dust to separate winter snow from summer snow. To account for snow layers getting squeezed and thinned under their own weight, the researchers applied four separate equations used in other studies, and in all cases the corrected record shows at least a doubling of snowfall.
According to the paper, while numerous snow accumulation records exist, "to our knowledge, no other alpine ice core accumulation record has been developed with such a thorough characterization of the thinning regime or uncertainties; all of the thinning models produce a robust increase in accumulation since the mid-19th century above late-Holocene background values."
The researchers note that the findings imply that regions that are sensitive to warming tropical ocean waters may continue to experience rain and snowfall variability well outside the natural range of the past millennium.
"Climate change can impact specific regions in much more extreme ways than global averages indicate because of unexpected responses from features like the Aleutian Low," said Osterberg. "The Mount Hunter record captures the dramatic changes that can occur when you get a double whammy from climate change – warming air combined with more storms from warming ocean temperatures."
However, the researchers also note that the regional findings do not necessarily mean that the same level of snowfall increases will occur elsewhere throughout the mid- and high latitudes.
"Scientists keep discovering that on a regional basis, climate change is full of surprises. We need to understand these changes better to help communities prepare for what will come with even more carbon dioxide pollution in the air," said Osterberg.
As part of the analysis, the authors suggest that current climate models underestimate the sensitivity of North Pacific atmospheric connections to warming tropical ocean temperatures. They argue that refining the way the modeled atmosphere responds to tropical ocean temperatures may improve rain and snowfall predictions in a warming world.
This research was supported by the NSF (National Science Foundation) Paleoclimate Program (P2C2).
Artic Sea Loss Threatens to Dry Out California
December 2017: Arctic sea ice loss of the magnitude expected in the next few decades could impact California's rainfall and exacerbate future droughts, according to new research led by LLNL (Lawrence Livermore National Laboratory) scientists. 3)
The dramatic loss of Arctic sea ice cover observed over the satellite era is expected to continue throughout the 21st century. Over the next few decades, the Arctic Ocean is projected to become ice-free during the summer. A new study by Ivana Cvijanovic and colleagues from LLNL and University of California, Berkeley shows that substantial loss of Arctic sea ice could have significant far-field effects, and is likely to impact the amount of precipitation California receives. The research appears in the Dec. 5 edition of Nature Communications. 4)
The study identifies a new link between Arctic sea ice loss and the development of an atmospheric ridging system in the North Pacific. This atmospheric feature also played a central role in the 2012-2016 California drought and is known for steering precipitation-rich storms northward, into Alaska and Canada, and away from California. The team found that sea ice changes can lead to convection changes over the tropical Pacific. These convection changes can in turn drive the formation of an atmospheric ridge in the North Pacific, resulting in significant drying over California.
"On average, when considering the 20-year mean, we find a 10-15 percent decrease in California's rainfall. However, some individual years could become much drier, and others wetter," Cvijanovic said.
The study does not attribute the 2012-2016 drought to Arctic sea ice loss. However, the simulations indicate that the sea-ice driven precipitation changes resemble the global rainfall patterns observed during that drought, leaving the possibility that Arctic sea-ice loss could have played a role in the recent drought.
"The recent California drought appears to be a good illustration of what the sea-ice driven precipitation decline could look like," she explained.
California's winter precipitation has decreased over the last two decades, with the 2012-2016 drought being one of the most severe on record. The impacts of reduced rainfall have been intensified by high temperatures that have enhanced evaporation. Several studies suggest that recent Californian droughts have a manmade component arising from increased temperatures, with the likelihood of such warming-enhanced droughts expected to increase in the future.
"Our study identifies one more pathway by which human activities could affect the occurrence of future droughts over California — through human-induced Arctic sea ice decline," Cvijanovic said. "While more research should be done, we should be aware that an increasing number of studies, including this one, suggest that the loss of the Arctic sea ice cover is not only a problem for remote Arctic communities, but could affect millions of people worldwide. Arctic sea ice loss could affect us, right here in California."
Other co-authors on the study include Benjamin Santer, Celine Bonfils, Donald Lucas and Susan Zimmerman from LLNL and John Chiang from the University of California, Berkeley.
The research is funded by DOE (Department of Energy) Office of Science. Cvijanovic and Bonfils were funded by the DOE Early Career Research Program Award and Lucas is funded by the DOE Office of Science through the SciDAC project on Multiscale Methods for Accurate, Efficient and Scale-Aware Models of the Earth System.
Wildfires More Frequent in Canadian Boreal Forests due to Lightning
December 2017: Wildfires in the boreal forests of northern Canada and Alaska have been increasing in frequency and the amount of area burned, and the drivers of large fire years are still poorly understood. But recent NASA-funded research offers at least one possible cause: more lightning. As global warming continues, lightning storms and warmer conditions are expected to spread farther north, meaning fire could significantly alter the landscape over time. 5)
A record number of lightning-ignited fires burned in Canada's Northwest Territories in 2014 and in Alaska in 2015. Scientist Sander Veraverbeke (Vrije Universiteit Amsterdam and University of California, Irvine) and colleagues examined data from satellites and from ground-based lightning networks to see if they could figure out why those seasons were so bad.
The team found that the majority of fires in their study areas in 2014 and 2015 were ignited by lightning storms, as opposed to human activity. That is natural, given the remoteness of the region, but it also points to more frequent lightning strikes in an area not known for as many thunderstorms as the tropics or temperate regions. Looking at longer trends, the researchers found that lightning-ignited fires in the region have been increasing by 2 to 5 percent per year since 1975, a trend that is consistent with climate change. The study was published in July 2017 in the journal Nature Climate Change. 6)
"We found that it is not just a matter of more burning with higher temperatures. The reality is more complex," Veraverbeke said. "Higher temperatures also spur more thunderstorms. Lightning from these thunderstorms is what has been igniting many more fires in these recent extreme events."
The map of Figure 5 shows the location and ignition source (lightning or human caused) for forest fires in interior Alaska in 2015. The map of Figure 6 shows the timing of the fires (June, July, or August) within the inset box. Both maps are based on data from the Veraverbeke study, which combined observations from the Alaska Fire Emissions Database, computer models, and fire observations from the MODIS (Moderate Resolution Imaging Spectroradiometer) instruments on NASA's Terra and Aqua satellites.
The fire season in the far north has typically peaked in July, after the spring thaw and the melting of winter snow. As global temperatures continue to rise, especially in the polar regions, thawing and warming tend to happen earlier in the spring and summer and at a more extensive level than in the past. The warmer weather also leads to more atmospheric instability, bringing more thunderstorms. The researchers asserted in the paper that "extreme fire years result when high levels of lightning ignition early in the growing season are followed by persistent warm and dry conditions that accelerate fire spread later in midsummer."
Brendan Rogers of the Woods Hole Research Center said these trends are likely to continue. "We expect an increasing number of thunderstorms, and hence fires, across the high latitudes in the coming decades as a result of climate change."
The researchers also found that wildfires are creeping farther north, closer to the transition zone between boreal forests and Arctic tundra. Together, these areas include at least 30 percent of the world's tree cover and 35 percent of its stored soil carbon.
"In these high-latitude ecosystems, permafrost soils store large amounts of carbon that become vulnerable after fires pass through," said James Randerson of UC Irvine. "Exposed mineral soils after tundra fires also provide favorable seedbeds for trees migrating north under a warmer climate."
"Taken together, we discovered a complex feedback loop between climate, lightning, fires, carbon and forests that may quickly alter northern landscapes," Veraverbeke said. "A better understanding of these relationships is critical to better predict future influences from climate on fires and from fires on climate."
Study co-author Charles Miller of NASA/JPL (Jet Propulsion Laboratory) added that while data from the lightning networks were critical to this study, it is challenging to use these data for trend detection because of continuing network upgrades. "A spaceborne sensor that provides high northern latitude lightning data would be a major step forward."
Global Carbon Budget 2017
November 2017: Following three years of no growth, global GHG (Greenhouse Gas) emissions from human activities are projected to increase by 2% by the end of 2017, according to the nongovernmental organization GCP (Global Carbon Project). The increase, to a record 37 billion tons of carbon dioxide equivalent, dashed hopes in the environmental community that CO2 emissions from human activity might have plateaued and begun turning downward. 7)
In a set of three reports published 13 November, GCP said the biggest cause of the increase is the 3.5% growth in China, the world's largest emitter of greenhouse gases. The country experienced higher energy demand, particularly from industry, and a decline in hydroelectric power due to sparse rainfall. 8) 9) 10)
In addition, the decade-long trend in emissions reductions by the US and the European Union, the second- and third-largest emitters, respectively, appears to have slowed this year. The EU's output hasn't declined appreciably since 2015. The US output declined by 0.4%, compared with a 1.2% average annual reduction during the previous 10 years. Coal consumption in the US inched up 0.5%, its first increase in five years.
India, the fourth-largest greenhouse gas emitter, limited its growth to 2% this year, compared with a 6% jump in 2016. Emissions from all other countries increased 2.3% from 2016, to 15.1 gigatons (Figure 9).
Despite the 2014–16 hiatus in global emissions growth, CO2 has continued to accumulate in the atmosphere at a faster pace than at any time during the 50 years that measurements have been kept. The elevated global temperatures resulting from the 2015–16 El Niño diminished the capacity of terrestrial ecosystems to take up CO2 from the atmosphere, the GCP reports said.
Corinne Le Quéré of the University of East Anglia (Norwich, UK), lead author of the principal report (Ref. 8) that was published in Earth System Science Data, said in an email that she expects emissions to plateau or grow slightly in the coming years. But they are unlikely to return to the 3% growth levels that were seen regularly in the decade that ended in 2010.
Kelly Levin of the nonprofit WRI (World Resources Institute) cautions against reading too much into a single year's data but also warns about the perilous big picture. "To have a chance of transforming the economy in time to stay below 2 °C, global GHG emissions must peak by 2020," she says. WRI's analysis, and another by the UNEP (United Nations Environment Program), predict on the basis of current trends and treaty commitments that the peak in global emissions won't occur until after 2030. At that point, the probability of limiting global warming to 2 °C could be as low as 50%, even with accelerated national reduction commitments, rapid abandonment of fossil fuel use, and deployment of carbon-removal technologies whose feasibility hasn't yet been demonstrated.
The 2 °C mark is thought by most climate scientists to be the threshold below which the worst impacts of climate change can be avoided. The 2015 Paris climate agreement set an "aspirational" goal of limiting temperature increase to 1.5 °C.
The WRI analysis says the number of countries whose emissions have peaked or are committed to peak will increase from 49 in 2010 to 53 by 2020 and to 57 by 2030. Those countries accounted for 36% of world greenhouse gas emissions in 2010 and will represent 60% of the total in 2030, when China has committed to peak its output.
Despite last year's emissions increase, China's coal consumption this year is still about 8% below its record 2013 high. The Chinese government has projected a near-doubling of the nation's solar energy production over the next two years, to 213 GW. China's nonfossil energy sources make up 14.3% of overall energy production, up by one percentage point in less than a year.
Study of Global Light Pollution at Night
November 22, 2017: They were supposed to bring about an energy revolution—but the popularity of LED (Light-Emitting Diode) lights is driving an increase in light pollution worldwide, with dire consequences for human and animal health, researchers said in their study. Five years of advanced satellite images show that there is more artificial light at night across the globe, and that light at night is getting brighter. The rate of growth is approximately two percent each year in both the amount of areas lit and the radiance of the light. 11) 12) 13)
An international team of scientists reported the results of a landmark study of global light pollution and the rise of LED outdoor lighting technology. The study finds both light pollution and energy consumption by lighting steadily increasing over much of the planet. The findings also challenge the assumption that increases in the energy efficiency of outdoor lighting technologies necessarily lead to an overall decrease in global energy consumption.
The team, led by Christopher Kyba of the GFZ (German Research Center for Geosciences) in Potsdam, Germany, analyzed five years of images from the Suomi NPP (Suomi National Polar-orbiting Partnership) satellite, operated jointly by NASA and NOAA (National Oceanic and Atmospheric Administration). The data show gains of 2% per year in both the amount of the Earth's surface that is artificially lit at night and the quantity of light emitted by outdoor lighting. Increases were seen almost everywhere the team looked into, with some of the largest gains in regions that were previously unlit.
"Light is growing most rapidly in places that didn't have a lot of light to start with," Kyba noted. "That means that the fastest rates of increase are occurring in places that so far hadn't been very strongly affected by light pollution."
The results reported today confirm suggestions in earlier research based on data obtained with U.S. Department of Defense meteorological satellite measurements (DMSP series) going back to the 1970s. However, the better sensitivity of Suomi's cameras to light on the night side of Earth and significantly improved ground resolution led to more robust conclusions about the changing illumination of the world at night.
The study is among the first to examine the effects, as seen from space, of the ongoing worldwide transition to LED lighting. Kyba's team found that the energy saving effects of LED lighting on country-level energy budgets are lower than expected from the increase in the efficiency of LEDs compared to older lamps.
Environmental Gains Unrealized : LED lighting requires significantly less electricity to yield the same quantity of light as older lighting technologies. Proponents of LED lighting have argued that the high energy efficiency of LEDs would contribute to slowing overall global energy demand, given that outdoor lighting accounts for a significant fraction of the nighttime energy budget of the typical world city.
The team tested this idea by comparing changes in nighttime lighting seen from Earth orbit to changes in countries' GDP (Gross Domestic Product) – a measure of their overall economic output – during the same time period. They concluded that financial savings from the improved energy efficiency of outdoor lighting appear to be invested into the deployment of more lights. As a consequence, the expected large reductions in global energy consumption for outdoor lighting have not been realized.
Kyba expects that the upward global trend in use of outdoor lighting will continue, bringing a host of negative environmental consequences. "There is a potential for the solid-state lighting revolution to save energy and reduce light pollution," he added, "but only if we don't spend the savings on new light".
IDA (International Dark-Sky Association) has campaigned for the last 30 years to bring attention to the known and suspected hazards associated with the use of artificial light at night. IDA Executive Director J. Scott Feierabend pointed out repercussions including harm to wildlife, threats to human wellbeing, and potentially compromised public safety. IDA drew public attention to concerns associated with the strong blue light emissions of LED lighting as early as 2010.
"Today's announcement validates the message IDA has communicated for years," Feierabend explained. "We hope that the results further sound the alarm about the many unintended consequences of the unchecked use of artificial light at night."
Satellite imagery: The VIIRS (Visible Infrared Imaging Radiometer Suite) DNB (Day-Night Band) of the Suomi NPP mission started observations in 2012 -just as outdoor use of LED lighting began in earnest. This sensor provides the first-ever global calibrated nighttime radiance measurements in a spectral band of 500 to 900 nm, which is close to the visible band, with a much higher radiometric sensitivity than the DMSP series, and at a spatial resolution of ~750 m. This improved spatial resolution allows neighborhood (rather than city or national) scale changes in lighting to be investigated for the first time.
The cloud-free DNB data show that over the period of 2012–2016, both lit area and the radiance of previously lit areas increased in most countries (Figure 11) in the 500–900 nm range, with global increases of 2.2% per year for lit area and 2.2% per year for the brightness of continuously lit areas. Overall, the radiance of areas lit above 5 nWcm-2 sr-1 increased by 1.8% per year. These factors decreased in very few countries, including several experiencing warfare. They were also stable in only a few countries, interestingly including some of the world's brightest (for example, Italy, Netherlands, Spain, and the United States). With few exceptions, growth in lighting occurred throughout South America, Africa, and Asia. Because the analysis of lit area and total radiance is not subject to a stability criterion, transient lights such as wildfires can cause large fluctuations.
Australia experienced a major decrease in lit area from 2012 to 2016 for this reason(Figures 11A and 12). However, fire-lit areas failed the stability test and were therefore not included in the radiance change analysis (Figure 11B). A small number of countries have "no data" because of either their extreme latitude (Iceland) or the lack of observed stable lights above 5 nWcm-2 sr-1 in the cloud-free composite (for example, Central African Republic).
Comparisons of the VIIRS data with photographs taken from aboard the ISS (International Space Station) show that the instrument on Suomi-NPP sometimes records a dimming of some cities even though these cities are in fact the same in brightness or even more brightly lit. The reason for this is that sensor can't "see" light at wavelengths below 500 nm, i.e. blue light. When cities replace orange lamps with white LED lights that emit considerable radiation below 500 nm, VIIRS mistakes the change for a decrease. In short: The Earth's night-time surface brightness and especially the skyglow over cities is increasing, probably even in the cases where the satellite detects less radiation. 14)
There is, however, hope that things will change for the better. Christopher Kyba says: "Other studies and the experience of cities like Tucson, Arizona, show that well designed LED lamps allow a two-third or more decrease of light emission without any noticeable effect for human perception." Kyba's earlier work has shown that the light emission per capita in the United States of America is 3 to 5 times higher than that in Germany. Kyba sees this as a sign that prosperity, safety, and security can be achieved with conservative light use. "There is a potential for the solid state lighting revolution to save energy and reduce light pollution," adds Kyba, "but only if we don't spend the savings on new light."
The Changing Colors of our Living Planet
Life. It's the one thing that, so far, makes Earth unique among the thousands of other planets we've discovered. Since the fall of 1997, NASA satellites have continuously and globally observed all plant life at the surface of the land and ocean. During the week of Nov. 13-17, NASA is sharing stories and videos about how this view of life from space is furthering knowledge of our home planet and the search for life on other worlds. 15)
NASA satellites can see our living Earth breathe. In the Northern Hemisphere, ecosystems wake up in the spring, taking in carbon dioxide and exhaling oxygen as they sprout leaves — and a fleet of Earth-observing satellites tracks the spread of the newly green vegetation.
Meanwhile, in the oceans, microscopic plants drift through the sunlit surface waters and bloom into billions of carbon dioxide-absorbing organisms — and light-detecting instruments on satellites map the swirls of their color.
This fall marks 20 years since NASA has continuously observed not just the physical properties of our planet, but the one thing that makes Earth unique among the thousands of other worlds we've discovered: Life.
Satellites measured land and ocean life from space as early as the 1970s. But it wasn't until the launch of SeaWiFS (Sea-viewing Wide Field-of-view Sensor) in 1997 that the space agency began what is now a continuous, global view of both land and ocean life. A new animation captures the entirety of this 20-year record, made possible by multiple satellites, compressing a decades-long view of life on Earth into a captivating few minutes.
"These are incredibly evocative visualizations of our living planet," said Gene Carl Feldman, an oceanographer at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "That's the Earth, that is it breathing every single day, changing with the seasons, responding to the Sun, to the changing winds, ocean currents and temperatures."
The space-based view of life allows scientists to monitor crop, forest and fisheries health around the globe. But the space agency's scientists have also discovered long-term changes across continents and ocean basins. As NASA begins its third decade of global ocean and land measurements, these discoveries point to important questions about how ecosystems will respond to a changing climate and broad-scale changes in human interaction with the land.
Satellites have measured the Arctic getting greener, as shrubs expand their range and thrive in warmer temperatures. Observations from space help determine agricultural production globally, and are used in famine early warning detection. As ocean waters warm, satellites have detected a shift in phytoplankton populations across the planet's five great ocean basins — the expansion of "biological deserts" where little life thrives. And as concentrations of carbon dioxide in the atmosphere continue to rise and warm the climate, NASA's global understanding of plant life will play a critical role in monitoring carbon as it moves through the Earth system.
Sixty years ago, people were not sure that Earth's surface could be seen clearly from space. Many thought that the dust particles and other aerosols in the atmosphere would scatter the light, masking the oceans and continents, said Jeffrey Masek, chief of the Biospheric Sciences Laboratory at NASA Goddard.
The Gemini and Apollo programs demonstrated otherwise. Astronauts used specialized cameras to take pictures of Earth that show the beauty and complexity of our living planet, and helped kickstart the era of Earth science research from space. In 1972, the first Landsat mission began its 45-year record of vegetation and land cover. "As the satellite archive expands, you see more and more dynamics emerging," Masek said. "We're now able to look at long-term trends."
The grasslands of Senegal, for example, undergo drastic seasonal changes. Grasses and shrubs flourish during the rainy season from June to November, then dry up when the rain stops. With early weather satellite data in the 1970s and '80s, NASA Goddard scientist Compton Tucker was able to see that greening and die-back from space, measuring the chlorophyll in the plants below. He developed a way of comparing satellite data from two wavelengths, which gives a quantitative measurement of this greenness called the NDVI (Normalized Difference Vegetation Index).
"We were astounded when we saw the first images. They were amazing because they showed how vegetation changed annually, year after year," Tucker said, noting that others were surprised as well when the study came out in 1985. "When we produced this paper, people accused us of ‘painting by numbers,' or fudging data. But for the first time, you could study vegetation from space based on their photosynthetic capacity."
When the temperature is right, and water and sunlight are available, plants photosynthesize and produce vegetative material. Leaves strongly absorb blue and red light but reflect near-infrared light back into space. By comparing the ratio of red to near-infrared light, Tucker and his colleagues could quantify the vegetation covering the land.
Expanding these observations to the rest of the globe, the scientists could track the impact on plants of rainy and dry seasons elsewhere in Africa, see the springtime blooms in North America, and the after-effects of wildfires in forests worldwide.
But land is only part of the story. At the base of the ocean's food web is phytoplankton — tiny organisms that, like land plants, turn water and carbon dioxide into sugar and oxygen, aided by the right combination of nutrients and sunlight.
Satellites that can monitor the subtle changes in color of the ocean have helped scientists track changes in phytoplankton populations across the globe. The first view of ocean color came from the CZCS (Coastal Zone Color Scanner), a proof-of concept instrument launched in 1979. Continuous observations of ocean color began with the launch of SeaWIFS in late 1997. The satellite was just in time to capture the transition from El Niño to La Niña conditions in 1998 — revealing just how quickly and dramatically phytoplankton respond to changing ocean conditions.
"The entire Eastern Pacific, from the coast of South America all the way to the dateline, transitioned from what was the equivalent of a biological desert to a thriving rainforest. And we watched it happen in real time," Feldman said. "For me, that was the first demonstration of the power of this kind of observation, to see how the ocean responds to one of the most significant environmental perturbations it could experience, over the course of just a few weeks. It also showed that the ocean and all the life within it is amazingly resilient — if given half a chance."
Tracking change from satellites: With 20 years of satellite data tracking ocean plant life on a global scale, scientists are investigating how habitats and ecosystems are responding to changing environmental conditions.
Recent studies of ocean life have shown that a long-term trend of rising sea surface temperatures is causing ocean regions known as "biological deserts" to expand. These regions of low phytoplankton growth occur in the center of large, slow-moving currents called gyres.
"As the surface waters warm, it creates a stronger boundary between the deep, cold, nutrient-rich waters and the sunlit, generally nutrient-poor surface waters," Feldman said. This prevents nutrients from reaching phytoplankton at the surface, and could have significant consequences for fisheries and the marine ecosystem.
In the Arctic Ocean, an explosion of phytoplankton indicates change. As seasonal sea ice melts, warming waters and more sunlight will trigger a sudden, massive phytoplankton bloom that feeds birds, sea lions and newly hatched fish. But with warming atmospheric temperatures, that bloom is now happening several weeks early — before the animals are in place to take advantage of it. "It's not just the amount of food, it's the location and timing that are just as critical," Feldman said. "Spring bloom is coming earlier, and that's going to impact the ecosystem in ways we don't yet understand."
The climate is warming fastest in Arctic regions, and the impacts on land are visible from space as well. The tundra of Western Alaska, Quebec and elsewhere is turning greener as shrubs extend their reach northwards.
The neighboring northern forests are changing as well. Massive fires in 2004 and 2015 wiped out millions of acres of forests in Alaska, including spruce forests, noted Chris Potter, a research scientist at NASA's Ames Research Center in California's Silicon Valley. "These fires were amazing in the amount of forest area they burned and how hot they burned," Potter said. "When the air temperature hits 90 degrees Fahrenheit (32ºC) in late May up there, and all these lightning strikes occurred, the forest burned very extensively — close to rivers, close to villages — and nothing could stop it."
Satellites help scientists routinely map fires, deforestation and other changes, and to analyze their impact on the carbon cycle, Potter said. Giant fires release many tons of carbon dioxide into the atmosphere, both from the charred trees and moss but also, especially in northern latitudes, from the soils. Potter and colleagues went to the burned areas of Central Alaska this year to measure the underlying permafrost — the thick mossy layer had burned off, exposing the previously frozen soils. "It's like taking the insulating layer off a cooler," he said. "The ice melts underneath and it becomes a slushy mess."
Forest types can change too, whether it's after wildfires, insect infestations or other disturbance. The Alaskan spruce forests are being replaced with birch. Potter and his colleagues are also keeping an eye on California forests burned in recent fires, where the concern is that pines will be replaced by oaks. "When drought is accentuated with these record high temperatures, nothing good seems to come from that for the existing forest type," he said. "I think we're seeing real clear evidence of climate causing land-cover change."
Keeping an eye on crops: Changing temperatures and rainfall patterns also influence crops, whether they are grown in California or Africa. The "greenness" measurement that scientists use to measure forests and grasslands can also be used for agriculture, to monitor the health of fields throughout the growing season.
Researchers and policy makers realized this potential early. One of the first applications of Landsat data in the 1970s was to predict grain yields in Russia and better understand commodities markets. In 1985, food security analysts from USAID (United States Agency for International Development) approached NASA to incorporate satellite images into their Famine Early Warning Systems Network, to identify regions where food production has been limited by drought. That partnership continues today. With rainfall estimates, vegetation measurements, as well as the recent addition of soil moisture information, NASA scientists can help organizations like USAID direct emergency help.
With improved data from Landsat, the MODIS instruments on NASA's Terra and Aqua spacecraft and other satellites, and by combining data from multiple sensors, researchers are now able to track the growth of crops in individual fields, Tucker said.
The view from space not only helps monitor crops, but can help improve agricultural practices as well. A winery in California, for example, uses individual pixels of Landsat data to determine when to irrigate and how much water to use.
The next step for NASA scientists is actually looking at the process of photosynthesis from space. When plants undergo that chemical process, some of the absorbed energy fluoresces faintly back, notes Joanna Joiner, a NASA Goddard research scientist. With satellites that detect signals in the very specific wavelengths of this fluorescence, and a fine-tuned analysis technique that blocks out background signals, Joiner and her colleagues can see where and when plants start converting sunlight into sugars. - "It was kind of a revelation that yes, you can measure it," Joiner said. An early study looked at the U.S. Corn Belt and found it fluoresces "like crazy," she said. "Those plants have some of the highest fluorescence rates on Earth at their peak."
Joiner and Tucker are using both the fluorescence data and vegetation indices to get the most information possible about plant growth at regional and global scales: "One of the big questions that still remains is how much carbon are the plants taking up, why does it vary year to year, and which areas are contributing to that variability," Joiner said.
Whether it's crops, forests or phytoplankton blooms, NASA scientists are tracking life on Earth. Just as satellites help researchers study the atmosphere, rainfall and other physical characteristics of the planet, the ever-improving view from above will allow them to study the interconnected life of the planet, Feldman said.
Study Bolsters Theory of Heat Source Under West Antarctica
November 7, 2017: A new NASA/JPL study adds evidence that a geothermal heat source, called a mantle plume, lies deep below Antarctica's Marie Byrd Land, explaining some of the melting that creates lakes and rivers under the ice sheet. Although the heat source isn't a new or increasing threat to the West Antarctic ice sheet, it may help explain why the ice sheet collapsed rapidly in an earlier era of rapid climate change, and why it is so unstable today. 16)
The research team was led by Helene Seroussi of the Jet Propulsion Laboratory, with support from researchers from the Department of Earth and Planetary Sciences at Washington University and the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research in Germany. 17)
The stability of an ice sheet is closely related to how much water lubricates it from below, allowing glaciers to slide more easily. Understanding the sources and future of the meltwater under West Antarctica is important for estimating the rate at which ice may be lost to the ocean in the future.
Antarctica's bedrock is laced with rivers and lakes, the largest of which is the size of Lake Erie. Many lakes fill and drain rapidly, forcing the ice sheet to rise and fall by as much as 6 meters. The motion allows scientists to estimate where and how much water must exist at the base.
Some 30 years ago, Wesley E. LeMasurier, a scientist at the University of Colorado Denver suggested that heat from a mantle plume under Marie Byrd Land might explain regional volcanic activity and a topographic dome feature. Very recent seismic imaging has supported this concept. When Hélène Seroussi of NASA's Jet Propulsion Laboratory in Pasadena, California, first heard the idea, however, "I thought it was crazy," she said. "I didn't see how we could have that amount of heat and still have ice on top of it."
With few direct measurements existing from under the ice, the research team concluded the best way to study the mantle plume idea was by numerical modeling. They used the ISSM (Ice Sheet System Model), a numerical depiction of the physics of ice sheets developed by scientists at JPL and the University of California, Irvine. Seroussi enhanced the ISSM to capture natural sources of heating and heat transport from freezing, melting and liquid water; friction; and other processes.
To assure the model was realistic, the scientists drew on observations of changes in the altitude of the ice sheet surface made by NASA's IceSat satellite and airborne Operation IceBridge campaign. "These place a powerful constraint on allowable melt rates — the very thing we wanted to predict," Ivins said. Since the location and size of the possible mantle plume were unknown, they tested a full range of what was physically possible for multiple parameters, producing dozens of different simulations.
They found that the flux of energy from the mantle plume must be no more than 150 mW/m2. For comparison, in U.S. regions with no volcanic activity, the heat flux from Earth's mantle is 40 to 60 mW. Under Yellowstone National Park — a well-known geothermal hot spot — the heat from below is about 200 mW/m2 averaged over the entire park, though individual geothermal features such as geysers are much hotter.
The research team's simulations, using a heat flow higher than 150 mW/m2, showed too much melting to be compatible with the space-based data, except in one location: an area inland of the Ross Sea known for intense flows of water. This region required a heat flow of at least 150-180 mW/m2 to agree with the observations. However, seismic imaging has shown that mantle heat in this region may reach the ice sheet through a rift, that is, a fracture in Earth's crust such as appears in Africa's Great Rift Valley.
Mantle plumes are thought to be narrow streams of hot rock rising through Earth's mantle and spreading out like a mushroom cap under the crust. The buoyancy of the material, some of it molten, causes the crust to bulge upward. The theory of mantle plumes was proposed in the 1970s to explain geothermal activity that occurs far from the boundary of a tectonic plate, such as Hawaii and Yellowstone.
The Marie Byrd Land mantle plume formed 50 to 110 million years ago, long before the West Antarctic ice sheet came into existence. At the end of the last ice age around 11,000 years ago, the ice sheet went through a period of rapid, sustained ice loss when changes in global weather patterns and rising sea levels pushed warm water closer to the ice sheet — just as is happening today. The research team suggests the mantle plume could facilitate this kind of rapid loss.
Ozone Hole in 2017 is Smallest Since 1988
Observations in 2017 showed that the "hole" in Earth's ozone layer—which forms over Antarctica at the end of each southern winter—was the smallest recorded since 1988. - According to NASA satellite estimates, the ozone hole reached its annual peak extent on September 11, spreading across 19.6 million km2, an area about 2.5 times the size of the United States. Ground- and balloon-based measurements from the NOAA (National Oceanic and Atmospheric Administration) agreed with the satellite measurements. The average area of ozone hole maximums since 1991 has been roughly 26 million km2. 18)
"The Antarctic ozone hole was exceptionally weak this year," said Paul Newman, chief scientist for Earth sciences at NASA/GSFC. "This is what we would expect to see given the weather conditions in the Antarctic stratosphere."
The smaller ozone hole in 2017 was strongly influenced by an unstable and warmer-than-usual Antarctic vortex, a low-pressure system that rotates clockwise in the atmosphere over far southern latitudes (similar to polar vortices in the northern hemisphere). The vortex helped minimize the formation of PSCs (Polar Stratospheric Clouds); the formation and persistence of PSCs are important precursors to the chlorine- and bromine reactions that destroy ozone.
Although warmer stratospheric weather conditions have reduced ozone depletion during the past two years, ozone holes are still large because atmospheric concentrations of ozone-depleting substances (primarily chlorine and bromine) remain high enough to produce significant yearly ozone loss. The smaller ozone hole extent in 2017 is due to natural variability and not necessarily a signal of rapid healing.
First detected in 1985, the Antarctic ozone hole forms during late winter in the Southern Hemisphere as returning sunlight catalyzes reactions involving man-made, chemically active forms of chlorine and bromine. These reactions destroy ozone molecules in the stratosphere. At high altitudes, the ozone layer acts like a natural sunscreen, shielding the Earth's surface from harmful ultraviolet radiation that can cause skin cancer and cataracts, suppress immune systems, and damage plants.
Thirty years ago, the international community signed the Montreal Protocol on Substances that Deplete the Ozone Layer and began regulating ozone-depleting compounds. The ozone hole over Antarctica is expected to gradually become less severe as chlorofluorocarbons (CFCs) continue to decline. Scientists expect the Antarctic ozone hole to recover back to 1980 levels by 2070.
Legend to Figures 16 and 17: The uneven seam in the contours of the data (lower left quadrant) marks the location of the international date line. Ozone data are measured by polar-orbiting satellites that collect observations in a series of swaths over the course of the day; the passes are generally separated by about 90 minutes. Stratospheric circulation slowly shifts the contours of the ozone hole over the course of the day (like winds shift the location of clouds). The contours move little from any one swath to the next, but by the end of the day, the cumulative movement is apparent at the date line.
As both images show, the word hole is not literal; scientists use it as a metaphor for the area in which ozone concentrations drop below the historical threshold of 220 Dobson Units. During the 1960s, long before the Antarctic ozone hole occurred, average ozone concentrations above the South Pole ranged from 260 to 320 Dobson Units. Globally, the ozone layer today ranges from 300 to 500 Dobson units.
"In the past, we've seen ozone at some stratospheric altitudes go to zero ozone by the end of September," said Bryan Johnson, NOAA atmospheric chemist. "This year, our balloon measurements showed the ozone loss rate stalled by the middle of September and ozone levels never reached zero."
Greenland Maps Show More Glaciers at Risk
November 1, 2017: New maps of Greenland's coastal seafloor and bedrock beneath its massive ice sheet show that two to four times as many coastal glaciers are at risk of accelerated melting as previously thought (Figure 18). Researchers at UCI ( University of California at Irvine), NASA and 30 other institutions have published the most comprehensive, accurate and high-resolution relief maps ever made of Greenland's bedrock and coastal seafloor. Among the many data sources incorporated into the new maps are data from NASA's OMG (Ocean Melting Greenland) campaign. 19) 20)
Lead author Mathieu Morlighem of UCI had demonstrated in an earlier paper that data from OMG's survey of the shape and depth, or bathymetry, of the seafloor in Greenland's fjords improved scientists' understanding not only of the coastline, but of the inland bedrock beneath glaciers that flow into the ocean. That's because the bathymetry where a glacier meets the ocean limits the possibilities for the shape of bedrock farther upstream.
The nearer to the shoreline, the more valuable the bathymetry data are for understanding on-shore topography, Morlighem said. "What made OMG unique compared to other campaigns is that they got right into the fjords, as close as possible to the glacier fronts. That's a big help for bedrock mapping." Additionally, the OMG campaign surveyed large sections of the Greenland coast for the first time ever. In fjords for which there are no data, it's difficult to estimate how deep the glaciers extend below sea level.
The OMG data are only one of many datasets Morlighem and his team used in the ice sheet mapper, which is named BedMachine. Another comprehensive source is NASA's Operation IceBridge airborne surveys. IceBridge measures the ice sheet thickness directly along a plane's flight path. This creates a set of long, narrow strips of data rather than a complete map of the ice sheet. Besides NASA, nearly 40 other international collaborators also contributed various types of survey data on different parts of Greenland.
No survey, not even OMG, covers every glacier on Greenland's long, convoluted coastline. To infer the bed topography in sparsely studied areas, BedMachine averages between existing data points using physical principles such as the conservation of mass.
The new maps reveal that two to four times more oceanfront glaciers extend deeper than 200 m below sea level than earlier maps showed. That's bad news, because the top 200 m of water around Greenland comes from the Arctic and is relatively cold. The water below it comes from farther south and is 3º to 4º C warmer than the water above. Deeper-seated glaciers are exposed to this warmer water, which melts them more rapidly.
Morlighem's team used the maps to refine their estimate of Greenland's total volume of ice and its potential to add to global sea level rise, if the ice were to melt completely — which is not expected to occur within the next few hundred years. The new estimate is higher by 7 cm for a total of 7.42 m.
OMG Principal Investigator Josh Willis of JPL, who was not involved in producing the maps, said, "These results suggest that Greenland's ice is more threatened by changing climate than we had anticipated."
On Oct. 23, the five-year OMG campaign completed its second annual set of airborne surveys to measure, for the first time, the amount that warm water around the island is contributing to the loss of the Greenland ice sheet. Besides the one-time bathymetry survey, OMG is collecting annual measurements of the changing height of the ice sheet and the ocean temperature and salinity in more than 200 fjord locations. Morlighem looks forward to improving BedMachine's maps with data from the airborne surveys.
Melting Snow Aids Absorption of Carbon Dioxide
October 30, 2017: It appears that something good can come from something bad. Although rising global temperatures are causing seasonal snow cover to melt earlier in the spring, this allows for the snow-free boreal forests to absorb more carbon dioxide from our atmosphere.
Scientists believe that global warming is primarily caused by carbon dioxide emissions from human activities such as burning coal, the oil and gas industry, transportation and domestic heating. As global temperatures rise, we see changes in Earth's climate such as the accelerated melting of glaciers, rising sea levels and an increase in the frequency of extreme weather conditions.
To predict the increase of carbon dioxide in the atmosphere accurately, scientists need to consider both the sources of emissions as well as the absorption of carbon dioxide both on land and in the oceans. Boreal forests are well known to be an important carbon sink on land, but the amount of carbon these high-latitude northern forests can absorb is influenced by the amount of snow cover.
To help quantify changes in carbon absorption, ESA's GlobSnow project produced daily snow cover maps over the whole northern hemisphere from 1979 to 2015 using satellites. -A team of climate and remote sensing scientists led by the (FMI (Finnish Meteorological Institute) recently analyzed the information and found that the start of plant growth in the spring has shifted earlier by an average of eight days over the last 36 years. 21) 22)
By combining this information with ground-based observations of the atmosphere–ecosystem carbon dioxide exchange from forests in Finland, Sweden, Russia and Canada, the team found that this earlier start to spring growth has increased the forest uptake of carbon dioxide from the atmosphere by 3.7% per decade. This acts as a brake on the growth of atmospheric carbon dioxide, helping to mitigate the rapid increase of carbon dioxide from man-made emissions.
The research team also found that the shift in spring recovery is much larger in Eurasian forests, leading to double the increase in carbon uptake compared to North American forests.
"Satellite data played an essential role in providing information on variability in the carbon cycle," said Prof. Jouni Pulliainen, who led the research team at the Finnish Meteorological Institute. "By combining satellite- and ground-based information, we were able to turn observations of melting snow into higher-order information on springtime photosynthetic activity and carbon uptake."
These new results will now be used to improve climate models and help to increase the accuracy in predictions of global warming.
Next year, ESA plans to improve the satellite-based record of global snow cover with the upcoming Snow_cci project of ESA's CCI (Climate Change Initiative).
Future Temperature and Soil Moisture May Alter Location of Agricultural Regions
October 2017: Future high temperature extremes and soil moisture conditions may cause some regions to become more suitable for rainfed, or non-irrigated, agriculture, while causing other areas to lose suitable farmland, according to a new USGS (U.S. Geological Survey study). 23)
These future conditions will cause an overall increase in the area suitable to support rainfed agriculture within dryland areas. Increases are projected in North America, western Asia, eastern Asia and South America. In contrast, suitable areas are projected to decline in European dryland areas.
This study focused on understanding and projecting suitability for rainfed agriculture in temperate, or non-tropical, dryland regions. Drylands make up at least 40 percent of the earth's land area and rainfed croplands account for approximately 75 percent of global cropland. Worldwide, temperate regions account for 31 percent of the area used to grow wheat and 17 percent used for corn. - "Understanding the future potential distribution of rainfed agriculture is important for resource managers in meeting economic and food security needs, especially as the earth's population grows," said USGS scientist and lead author of the study, John Bradford. 24)
Future climate conditions are expected to increase the frequency of high temperature events and alter the seasonality of soil moisture in dryland systems, which are the factors found to be important in predicting regions suitable for agriculture in these water-limited areas. Findings for the temperate regions examined by this study indicate that many areas currently too cold for agriculture, particularly across Asia and North America, will likely become suitable for growing crops. However, some areas that are currently heavily cultivated, including regions of the United States such as the southern Great Plains, are likely to become less suitable for agriculture in the future.
USGS scientists and an international team of collaborators from Switzerland, Germany, China, Canada and several U.S. universities found that rainfed agriculture is abundant in areas with adequate soil moisture but restricted in areas with regular high temperature extremes. Bradford and collaborators simulated future soil moisture and temperature conditions, and utilized these results to identify where rainfed agriculture may be located in the future. Scientists referenced previously published estimates of rainfed agriculture areas generated using satellite remote sensing. Models were used to determine conditions that support current rainfed agriculture, as well as future suitability under altered climate conditions.
"Our results indicate the interaction of soil moisture and temperature extremes provides a powerful yet simple framework for understanding the conditions that define suitability for rainfed agriculture in drylands," said Bradford. "Integrating this framework with long-term projections that include rising temperature and changing soil moisture patterns reveals potentially important future shifts in areas that could support agriculture in the absence of irrigation."
Within the dryland regions that were the focus of this study, areas suitable for agriculture are those that experience relatively long periods of moist soils and reasonably warm temperatures. In contrast, areas that frequently experience extreme air temperatures above 93 degrees Fahrenheit are less suitable for rainfed agriculture, even if sufficient moisture is available. Even for relatively cool dryland areas, periods of high temperatures during the growing season can negatively affect agriculture suitability.
October 2017: Atmospheric chemistry and physics study reveals new threat to the ozone layer
"Ozone depletion is a well-known phenomenon and, thanks to the success of the Montreal Protocol, is widely perceived as a problem solved," says University of East Anglia's David Oram. But an international team of researchers, led by Oram, has now found an unexpected, growing danger to the ozone layer from substances not regulated by the treaty. The study is published in Atmospheric Chemistry and Physics, a journal of the EGU (European Geosciences Union). 25)
Thirty years ago, the Montreal Protocol was agreed to phase-out chemicals destroying the ozone layer, the UV-radiation shield in the Earth's stratosphere. The treaty has helped the layer begin the slow process of healing, lessening the impact to human health from increased exposure to damaging solar radiation. But increasing emissions of ozone-destroying substances that are not regulated by the Montreal Protocol are threatening to affect the recovery of the layer, according to the new research.
The substances in question were not considered damaging before as they were "generally thought to be too short-lived to reach the stratosphere in large quantities," explains Oram, a research fellow of the UK's National Centre for Atmospheric Science. The new Atmospheric Chemistry and Physics study raises the alarm over fast-increasing emissions of some of these very short-lived chemicals in East Asia, and shows how they can be carried up into the stratosphere and deplete the ozone layer.
Emissions of ozone-depleting chemicals in places like China are especially damaging because of cold-air surges in East Asia that can quickly carry industrial pollution into the tropics. "It is here that air is most likely to be uplifted into the stratosphere," says co-author Matt Ashfold, a researcher at the University of Nottingham Malaysia Campus. This means the chemicals can reach the ozone layer before they are degraded and while they can still cause damage.
One of the new threats is dichloromethane, a substance with uses varying from paint stripping to agricultural fumigation and the production of pharmaceuticals. The amount of this substance in the atmosphere decreased in the 1990s and early 2000s, but over the past decade dichloromethane became approximately 60% more abundant. "This was a major surprise to the scientific community and we were keen to discover the cause of this sudden increase," says Oram.
"We expected that the new emissions could be coming from the developing world, where industrialization has been increasing rapidly," he says. The team set out to measure air pollution in East Asia to figure out where the increase in dichloromethane was coming from and if it could affect the ozone layer.
"Our estimates suggest that China may be responsible for around 50-60% of current global emissions [of dichloromethane], with other Asian countries, including India, likely to be significant emitters as well," says Oram.
The scientists collected air samples on the ground in Malaysia and Taiwan, in the region of the South China Sea, between 2012 and 2014, and shipped them back to the UK for analysis. They routinely monitor around 50 ozone-depleting chemicals in the atmosphere, some of which are now in decline as a direct consequence of the Montreal Protocol.
Dichloromethane was found in large amounts, and so was 1,2-dichloroethane, an ozone-depleting substance used to make PVC (Polyvinyl chloride). China is the largest producer of PVC, which is used in many construction materials, and its production in the country has increased rapidly in the past couple of decades. But the rise in dichloroethane emissions was unexpected and surprising because the chemical is both a "valuable commodity" and "highly toxic", says Oram. "One would expect that care would be taken not to release [dichloroethane] into the atmosphere."
Data collected from a passenger aircraft that flew over Southeast Asia between December 2012 and January 2014 showed that the substances weren't only present at ground level. "We found that elevated concentrations of these same chemicals were present at altitudes of 12 km over tropical regions, many thousands of kilometers away from their likely source, and in a region where air is known to be transferred into the stratosphere," says Oram.
Sample collection: 26)
Between 2012 and 2014, air samples were collected at various times (1) two coastal sites in Taiwan – Hengchun (22.0547º N, 120.6995º E) and Fuguei Cape (25.297º N, 121.538º E); (2) at the Bachok Marine Research Station on the north-east coast of Peninsular Malaysia (6.009º N, 102.425º E); and (3) during several flights of the IAGOS-CARIBIC aircraft between Germany and Thailand or Malaysia. IAGOS-CARIBIC (In-service Aircraft for a Global Observing System-Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) is a European project making regular measurements from an in-service passenger aircraft operated by Lufthansa (Airbus A340-600). The CARIBIC samples were all (n = 179) collected at altitudes between 10 and 12.3 km.
Note: IAGOS-CARIBIC is an innovative scientific project to study and monitor important chemical and physical processes in the Earth's atmosphere. Detailed and extensive measurements are made during long distance flights. CARIBIC deploys a modified airfreight container with automated scientific apparatus which are connected to an air and particle (aerosol) inlet underneath the aircraft. Using a passenger Airbus A340-600 from Lufthansa in total more than 530 flights are successfully completed. 27)
Legend to Figure 22: CH2Cl2 is one of a large group of halogenated compounds known as VSLSs (very short-lived substances). Owing to their relatively short atmospheric lifetimes (typically less than 6 months) and their correspondingly low OPDs (Ozone Depletion Potentials), VSLSs are not currently regulated by the Montreal Protocol.
Arctic Sea Ice Extent in the Autumn of 2017
• October 18, 2017: Every year, the process is generally the same: the cap of sea ice on the Arctic Ocean melts and retreats through spring and summer to an annual minimum extent. Then, as the ocean and air cool with autumn, ice cover grows again and the cycle continues. But when we take a look at smaller regions within the Arctic, we get a more detailed picture of what's been going on. 28)
The map of Figure 23 shows the extent of Arctic sea ice on September 13, 2017, when the ice reached its minimum extent for the year. Extent is defined as the total area in which the ice concentration is at least 15 percent. The map was compiled from observations by the AMSR-2 (Advanced Microwave Scanning Radiometer 2 instrument on the GCOM -W1 (Global Change Observation Mission 1st-Water)/Shizuku satellite mission, operated by JAXA (Japan Aerospace Exploration Agency). The yellow outline in Figure 23 shows the median sea ice extent observed in September from 1981 through 2010.
- According to the NSIDC (National Snow and Ice Data Center) in Boulder, CO, the Arctic sea ice cover in 2017 shrank to 4.64 million km2, the eighth-lowest extent in the 39-year satellite record. Charting these annual minimums and maximums has revealed a steep decline in overall Arctic sea ice in the satellite era. But the decline is not the same everywhere across the Arctic Ocean. The Beaufort Sea north of Alaska, for example, is the region where sea ice has been retreating the fastest.
- This year, ice in the Chukchi and Beaufort and seas reached their minimum extents toward the end of September, later than the Arctic as a whole. The graph of Figure 24 shows the ice in these two seas was still declining while other regions had started freezing. The melting persisted the longest in the Beaufort Sea, which finally started to refreeze after reaching a minimum on September 27. Data for the graph come from the NSIDC MASIE (Multi-sensor Analyzed Sea Ice Extent) product, which is based on operational sea ice analyses produced by the U.S. National Ice Center. Note: the MASIE observations included also the SSM/I instrument on the DMSP series. In addition, in situ measurements were used.
- Ice loss is the Beaufort and Chukchi seas was not record-breaking this year, but the extents were much lower than usual. Notice in the map how the ice edge in these seas was farther north than average. According to Walt Meier, a scientist at the NSIDC (National Snow and Ice Data Center), the Chukchi and Beaufort seas entered the melt season with a lot of first-year ice. This ice type is generally thinner than multi-year or perennial ice (which survived the previous melt season); first-year ice tends to melt away more easily.
- Meier also notes that low-pressure weather systems persisted near the North Pole for much of the summer. "Low pressure will keep things cooler overall and generally will lead to a relatively higher ice extent overall," Meier said. "However, the position of the low this year led to winds blowing from the south and west that help move ice out of these regions. Also, the winds may have helped to bring in warmer ocean waters from the Bering Strait region as well."
Causes of Earth's Recent Record Carbon Dioxide Spike
• October 12, 2017: A new NASA study provides spaceborne evidence that Earth's tropical regions were the cause of the largest annual increases in atmospheric carbon dioxide (CO2) concentration seen in at least 2,000 years. 29)
Scientists suspected the 2015-2016 El Niño — one of the largest on record — was responsible, but exactly how has been a subject of ongoing research. Analyzing the first 28 months of data from NASA's OCO-2 (Orbiting Carbon Observatory-2) satellite, researchers conclude impacts of El Niño-related heat and drought occurring in tropical regions of South America, Africa and Indonesia were responsible for the record spike in global carbon dioxide. The findings are published in the journal Science on 13 Oct. 2017 as part of a collection of five research papers based on OCO-2 data. 30) 31) 32) 33) 34) 35) 36)
"These three tropical regions released 2.5 gigatons more carbon into the atmosphere than they did in 2011," said Junjie Liu of NASA/JPL in Pasadena, California, who is lead author of the study. "Our analysis shows this extra carbon dioxide explains the difference in atmospheric carbon dioxide growth rates between 2011 and the peak years of 2015-2016. OCO-2 data allowed us to quantify how the net exchange of carbon between land and atmosphere in individual regions is affected during El Niño years." A gigaton (Gt = 109 tons) is a billion tons.
In 2015 and 2016, OCO-2 recorded atmospheric carbon dioxide increases that were 50 percent larger than the average increase seen in recent years preceding these observations. These measurements are consistent with those made by NOAA (National Oceanic and Atmospheric Administration). That increase was about 3 parts per million of carbon dioxide per year — or 6.3 gigatons of carbon. In recent years, the average annual increase has been closer to 2 parts per million of carbon dioxide per year — or 4 gigatons of carbon. These record increases occurred even though emissions from human activities in 2015-2016 are estimated to have remained roughly the same as they were prior to the El Niño, which is a cyclical warming pattern of ocean circulation in the central and eastern tropical Pacific Ocean that can affect weather worldwide.
Using OCO-2 data, Liu's team analyzed how Earth's land areas contributed to the record atmospheric carbon dioxide concentration increases. They found the total amount of carbon released to the atmosphere from all land areas increased by 3 gigatons in 2015, due to the El Niño. About 80 percent of that amount — or 2.5 gigatons of carbon — came from natural processes occurring in tropical forests in South America, Africa and Indonesia, with each region contributing roughly the same amount.
The team compared the 2015 findings to those from a reference year — 2011 — using carbon dioxide data from the GOSAT (Greenhouse Gases Observing Satellite) mission of JAXA (Japan Aerospace Exploration Agency). In 2011, weather in the three tropical regions was normal and the amount of carbon absorbed and released by them was in balance.
"Understanding how the carbon cycle in these regions responded to El Niño will enable scientists to improve carbon cycle models, which should lead to improved predictions of how our planet may respond to similar conditions in the future," said OCO-2 Deputy Project Scientist Annmarie Eldering of JPL. "The team's findings imply that if future climate brings more or longer droughts, as the last El Niño did, more carbon dioxide may remain in the atmosphere, leading to a tendency to further warm Earth."
While the three tropical regions each released roughly the same amount of carbon dioxide into the atmosphere, the team found that temperature and rainfall changes influenced by the El Niño were different in each region, and the natural carbon cycle responded differently. Liu combined OCO-2 data with other satellite data to understand details of the natural processes causing each tropical region's response.
In eastern and southeastern tropical South America, including the Amazon rainforest, severe drought spurred by El Niño made 2015 the driest year in the past 30 years. Temperatures also were higher than normal. These drier and hotter conditions stressed vegetation and reduced photosynthesis, meaning trees and plants absorbed less carbon from the atmosphere. The effect was to increase the net amount of carbon released into the atmosphere.
In contrast, rainfall in tropical Africa was at normal levels, based on precipitation analysis that combined satellite measurements and rain gauge data, but ecosystems endured hotter-than-normal temperatures. Dead trees and plants decomposed more, resulting in more carbon being released into the atmosphere. Meanwhile, tropical Asia had the second-driest year in the past 30 years. Its increased carbon release, primarily from Indonesia, was mainly due to increased peat and forest fires — also measured by satellite instruments.
"We knew El Niños were one factor in these variations, but until now we didn't understand, at the scale of these regions, what the most important processes were," said Eldering. "OCO-2's geographic coverage and data density are allowing us to study each region separately."
Scott Denning, professor of atmospheric science at Colorado State University in Fort Collins and an OCO-2 science team member who was not part of this study, noted that while scientists have known for decades that El Niño influences the productivity of tropical forests and, therefore, the forests' net contributions to atmospheric carbon dioxide, researchers have had very few direct observations of the effects. "OCO-2 has given us two revolutionary new ways to understand the effects of drought and heat on tropical forests: directly measuring carbon dioxide over these regions thousands of times a day; and sensing the rate of photosynthesis by detecting fluorescence from chlorophyll in the trees themselves," said Denning. "We can use these data to test our understanding of whether the response of tropical forests is likely to make climate change worse or not."
The concentration of carbon dioxide in Earth's atmosphere is constantly changing. It changes from season to season as plants grow and die, with higher concentrations in the winter and lower amounts in the summer. Annually averaged atmospheric carbon dioxide concentrations have generally increased year over year since the early 1800s — the start of the widespread Industrial Revolution. Before then, Earth's atmosphere naturally contained about 595 gigatons of carbon in the form of carbon dioxide. Currently, that number is 850 gigatons.
The annual increase in atmospheric carbon dioxide levels and the magnitude of the seasonal cycle are determined by a delicate balance between Earth's atmosphere, ocean and land. Each year, the ocean, plants and trees take up and release carbon dioxide. The amount of carbon released into the atmosphere as a result of human activities also changes each year. On average, Earth's land and ocean remove about half the carbon dioxide released from human emissions, with the other half leading to increasing atmospheric concentrations. While natural processes are responsible for the exchange of carbon dioxide between the atmosphere, ocean and land, each year is different. In some years, natural processes remove as little as 20 percent of human emissions, while in other years they scrub as much as 80 percent.
OCO-2, launched in 2014, gathers global measurements of atmospheric carbon dioxide with the resolution, precision and coverage needed to understand how this important greenhouse gas — the principal human-produced driver of climate change — moves through the Earth system at regional scales, and how it changes over time. From its vantage point in space, OCO-2 is able to make roughly 100,000 measurements of atmospheric carbon dioxide each day, around the world.
Institutions involved in the Liu study include JPL; NCAR (National Center for Atmospheric Research) in Boulder, Colorado; the University of Toronto; Colorado State University; Caltech in Pasadena, California; and Arizona State University in Tempe, AZ.
Monitoring of Groundwater Recovery in Silicon Valley
October 3, 2017: A NASA/university study finds aggressive conservation helped region's aquifer rebound quickly from one of the worst droughts in California history. Underground water reserves in California's Silicon Valley rebounded quickly from the state's recent severe drought, demonstrating the success of aggressive conservation measures, according to a new space-based study by NASA and university scientists. 38)
Using satellite data from COSMO-SkyMed, a constellation of four Italian Space Agency (Agenzia Spaziale Italiana, or ASI) satellites, a research team led by Estelle Chaussard at the University at Buffalo in New York, and including scientists from NASA/JPL (Jet Propulsion Laboratory) in Pasadena, California, used a technique called SAR (Synthetic Aperture Radar) interferometry to monitor the entire Santa Clara Valley aquifer near San Jose from 2011 to 2017. This type of radar can capture the subtle up-and-down movements of Earth's surface of just minute fractions, a few millimeters, that occur when water levels rise or fall underground. The scientists used hundreds of radar images obtained under a license from ASI to calculate how much the land surface elevation changed over time. The measurements show the aquifer began to rebound in late 2014, when the drought was still going strong, and that groundwater levels had returned to pre-drought levels by 2017, thanks to conservation measures that intensified in 2014, and heavy winter rains in 2016.
During the 2012-15 drought, the Santa Clara Valley Water District employed an array of conservation measures. These included restricting sprinkler use and asking customers to take shorter showers and convert lawns and pools into less-thirsty landscapes. The district also imported water from outside the region.
Chaussard says the actions may have helped stave off irreversible damage to the aquifer, which measures about 550 km2 and lies beneath a highly urbanized area. She explains when groundwater levels reach a record low, the porous sands and clays in which the reserves reside can dry up so much that the clays don't retain water anymore. The new study shows that thanks to the intensive water management efforts, this did not happen in the Santa Clara Valley.
Chaussard says the aquifer monitoring method her team used can work anywhere where there are soft-rock aquifer systems and where synthetic aperture radar satellite data are available, including in developing nations with few resources for monitoring. - "We wanted to see if we could use a remote sensing method that doesn't require ground monitoring to understand how our aquifers are responding to a changing climate and human activity," she says. "Our study further demonstrates the utility of SAR interferometry, which scientists also use to measure surface deformation related to volcanoes and earthquakes, for tracking ground deformation associated with changes in groundwater levels."
"This study further demonstrates a complementary method, in addition to traditional ground-based measurements, for water management districts to monitor ground deformation," added JPL co-author Pietro Milillo. "The technique marks an improvement over traditional methods because it allows scientists to gauge changes in ground deformation across a large region with unprecedented frequency." He said the COSMO-SkyMed satellites provided information for the aquifer as often as once a day.
Underground stockpiles of water — housed in layers of porous rock called aquifers — are one of the world's most important sources of drinking water. Some 2.5 billion people across the globe rely on aquifers for water, and many of these repositories are being drained more quickly than they can be refilled, according to the United Nations Educational, Scientific and Cultural Organization.
Yet keeping tabs on these precious reserves is expensive, says Chaussard. "To monitor aquifers, you need a lot of measurements in both space and time," she says. "Sampling water levels at wells may give you a continuous time series, but only if they are constantly monitored, and automated monitoring may not be common. Also, even a high density of wells may not adequately capture basin-wide spatial patterns of water storage, which is key to understanding processes at stake."
The methods employed in this study provide a more complete picture of how an aquifer responds during a drought and how water conservation methods can have a real and positive impact on sustaining the health and viability of pumped groundwater aquifers. The satellite radar imagery not only fills in data gaps between wells, but provides valuable insights into how aquifers are responding beyond the edges of monitoring well networks so that water agencies can more effectively manage their precious resources.
The upcoming NASA-ISRO (Indian Space Research Organization) Synthetic Aperture Radar (NISAR) satellite mission, planned for launch in 2021, will systematically collect radar imagery over nearly every aquifer in the world, improving our understanding of valuable groundwater resources and our ability to better manage them. In addition to tracking groundwater use in urban settings, NISAR will be able to measure surface motion associated with groundwater pumping and natural recharge in rural communities, in areas with extensive agriculture, and in regions with extensive vegetation, conditions that are typically more challenging.
The research was published Sept. 25 in the Journal of Geophysical Research - Solid Earth. Other participating institutions include the University of California, Berkeley; Purdue University, West Lafayette, Indiana; and the Santa Clara Valley Water District. 39)
Global Patterns of Drought Recovery
September 13, 2017: As global temperatures continue to rise, the prevailing wisdom in the climate science community is that droughts will grow more frequent and more extreme in the 21st century. Though temperatures were already rising in the 20th century, the global trend in drought length and severity was ambiguous, with no clear pattern. However, the impacts of droughts was less ambiguous, particularly in recent decades. 40)
In a study published in August 2017 in the journal Nature, researchers from 17 institutions found that more of Earth's land surface is now being affected by drought and ecosystems are taking longer to recover from dry spells. Recovery is particularly worse in the tropics and at high latitudes, two areas that are already pretty vulnerable to global change. 41)
The map of Figure is based on data from that study, which was led by Christopher Schwalm of WHRC (Woods Hole Research Center). It depicts the average length of time that it took for vegetation to recover from droughts that occurred between 2000 and 2010. The darkest colors mark the areas with the longest drought recovery time. Land areas colored light gray were covered by ice or sand (deserts).
Up until now, most assessments of drought and recovery have focused on the hydrology; that is, has new rain and snowfall made up for the deficit of water in rivers, lakes, and soils? In this new study, researchers focused on the health and resilience of the trees and other plants because full reservoirs and streams do not necessarily mean that vegetation has recovered.
The research team combined observations from the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite, ground measurements, and computer models to assess changes in drought. In particular, they measured changes in GPP (Gross Primary Productivity), or how well plants are consuming and storing carbon dioxide through photosynthesis. As the analysis showed, plants in many regions are taking longer to recover from drought, often because weather is more extreme (usually hotter) than in the past.
If the time between droughts grows shorter (as predicted) and the time to recover from them keeps growing longer, some ecosystems could reach a tipping point and change permanently. This could affect how much carbon dioxide is stored on land in trees and other vegetation (the land "carbon sink"). If less carbon is being captured and stored, then more of what humans produce would remain in the atmosphere, creating a feedback loop that amplifies the warming that leads to more drought.
"The most important implication of our study," said Schwalm, "is that under business-as-usual emissions of greenhouse gases, the time between drought events will likely become shorter than the time needed for recovery."
"Using the vantage point of space, we can see all of Earth's forests and other ecosystems getting hit repeatedly and increasingly by droughts," added co-author Josh Fisher of NASA's Jet Propulsion Laboratory. "Some of these ecosystems recover, but, with increasing frequency, others do not."
Researchers Find Direct Evidence of Sea Level 'fingerprints'
September 7, 2017: Researchers from NASA/JPL (Jet Propulsion Laboratory) in Pasadena, California, and the UCI (University of California), Irvine, have reported the first detection of sea level "fingerprints" in ocean observations: detectable patterns of sea level variability around the world resulting from changes in water storage on Earth's continents and in the mass of ice sheets. The results will give scientists confidence they can use these data to determine how much the sea level will rise at any point on the global ocean as a result of glacier ice melt. 42) 43)
As ice sheets and glaciers undergo climate-related melting, they alter Earth's gravity field, resulting in sea level changes that aren't uniform around the globe. For example, when a glacier loses ice mass, its gravitational attraction is reduced. Ocean waters nearby move away, causing sea level to rise faster far away from the glacier. The resulting pattern of sea level change is known as a sea level fingerprint. Certain regions, particularly in Earth's middle and low latitudes, are hit harder, and Greenland and Antarctica contribute differently to the process. For instance, sea level rise in California and Florida generated by the melting of the Antarctic ice sheet is up to 52 percent greater than its average effect on the rest of the world.
To calculate sea level fingerprints associated with the loss of ice from glaciers and ice sheets and from changes in land water storage, the team used gravity data collected by the twin satellites of the U.S./German GRACE (Gravity Recovery and Climate Experiment) between April 2002 and October 2014. During that time, the loss of mass from land ice and from changes in land water storage increased global average sea level by about 1.8 mm per year, with 43 percent of the increased water mass coming from Greenland, 16 percent from Antarctica and 30 percent from mountain glaciers. The scientists then verified their calculations of sea level fingerprints using readings of ocean-bottom pressure from stations in the tropics.
"Scientists have a solid understanding of the physics of sea level fingerprints, but we've never had a direct detection of the phenomenon until now," said co-author Isabella Velicogna, UCI professor of Earth system science and JPL research scientist. "It was very exciting to observe the sea level fingerprints in the tropics, far from the glaciers and ice sheets," said lead author Chia-Wei Hsu, a graduate student researcher at UCI.
GRACE is a joint NASA mission with the German Aerospace Center (DLR) and the German Research Center for Geosciences (GFZ), in partnership with the University of Texas at Austin.
Global Record Temperature Streak Study
August 10, 2017: The year 2016, aided in part by a historically large El Niño event, set a new global temperature record. We have thus witnessed three consecutive record breaking annual mean temperatures (2014, 2015, and 2016) in most global and/or hemispheric surface temperature series for the first time since historical observations began in the nineteenth century. It is reasonable to suspect that such an event would be extremely unlikely in the absence of anthropogenic warming, but it is worthwhile to ask just how unlikely such events actually are both with and without anthropogenic influence on climate. 44) 45)
Temperature records were first broken in 2014, when that year became the hottest year since global temperature records began in 1880. These temperatures were then surpassed in 2015 and 2016, making last year the hottest year ever recorded. In 2016, the average global temperature across land and ocean surface areas was 0.94 degrees Celsius above the 20th century average of 13.9 degrees Celsius,according to NOAA.
Winds Trigger Pond Growth
July 6, 2017: Wind is a force to be reckoned with. It can stir up monsoons, carry dust thousands of miles, and sculpt rock into sinuous arches. But sometimes, the effects of wind go unnoticed for years, like when it carves away slowly at the edges of a pond. 46)
A new study shows that winds are responsible for the widespread growth of ponds in three watersheds along the Mississippi River. The paper, published in April 2017 in Geophysical Research Letters, shows that wind-driven waves can erode pond banks, leading them to migrate in the direction of the wind. In effect, researchers have shown that wind-driven erosion, which nibbles away coastlines and the edges of larger bodies of water, can also happen inland on small scales. 47)
The researchers analyzed roughly 10,000 satellite images taken between 1982 and 2016, examining land and water pixels to look for inland change across the Mississippi River Delta. "Up until now, a lot of focus has been on coastal retreat," said Alejandra Ortiz, a marine geologist at Indiana University, Bloomington. Instead, Ortiz and colleagues focused on internal fragmentation; that is, what happens when land becomes subdivided by inland erosion processes. "Our thinking was, can you see this on large scale?"
Ortiz and her co-authors found that ponds in the Mississippi Delta tended to expand in a southwesterly direction, which is the same direction as the prevailing winds (which blow out of the northeast). This was especially true in Terrebonne and Barataria basins, where 80 percent of the ponds are expanding. The other study basin, the Atchafalaya-Vermillion, was deemed stable, with nearly as many ponds contracting as expanding—roughly 30 percent.
The false-color image of Figure 31 shows the area of study along the Atchafalaya Delta. It was captured on December 1, 2016, by OLI (Operational Land Imager) on Landsat 8. The colors emphasize the difference between land and water while allowing viewers to observe waterborne sediment, which is typically absent from false-color imagery.
The images of Figures 32 and 33 illustrate ponds that have grown (blue) or receded (orange) near the delta. In areas like Houma, Louisiana, the size of ponds increased significantly. The Terrebone and Barataria basins have much higher pond density, making them more susceptible to pond merging—when two or more ponds migrate toward each other and produce one larger body of water.
Some ponds were too small to generate waves strong enough to erode the shoreline. The researchers found that critical pond width was about 300 meters. Ponds at least that wide offer enough open space—for wind to gather momentum, or "fetch" as sailors and meteorologists call it—to create waves big enough to nibble away the shore.
Ortiz said the findings could affect the management of erosion-prone water bodies. For instance, managers could create physical barriers to prevent ponds from growing. "One possibility is thinking about putting in something that stops wave generation," she said.
Increasing Rate of Sea Level Rise, 1993-2014
June 2017: Ocean levels rose 50 percent faster in 2014 than in 1993, with meltwater from the Greenland ice sheet now supplying 25 percent of total sea level increase compared with just five percent 20 years earlier, researchers reported on June 26, 2017. The findings add to growing concern among scientists that the global watermark is climbing more rapidly than forecast only a few years ago, with potentially devastating consequences. 48)
- The findings add to growing concern among scientists that the global watermark is climbing more rapidly than forecast only a few years ago, with potentially devastating consequences. Hundreds of millions of people around the world live in low-lying deltas that are vulnerable, especially when rising seas are combined with land sinking due to depleted water tables, or a lack of ground-forming silt held back by dams.
- Major coastal cities are also threatened, while some small island states are already laying plans for the day their drowning nations will no longer be livable.
- "This result is important because the IPCC (Intergovernmental Panel on Climate Change), the UN science advisory body, makes a very conservative projection of total sea level rise by the end of the century," at 60 to 90 cm, said Peter Wadhams, a professor of ocean physics at the University of Oxford who did not take part in the research.
- That estimate, he added, assumes that the rate at which ocean levels rise will remain constant. "Yet there is convincing evidence — including accelerating losses of mass from Greenland and Antarctica — that the rate is actually increasing, and increasing exponentially."
- Greenland alone contains enough frozen water to lift oceans by about 7 m, though experts disagree on the global warming threshold for irreversible melting, and how long that would take once set in motion.
- "Most scientists now expect total rise to be well over 1 m by the end of the century," Wadhams said.
- The new study, published in Nature Climate Change, reconciles for the first time two distinct measurements of sea level rise. 49)
- GMSL has been rising at a faster rate during the satellite altimetry period (1993–2014) than previous decades, and is expected to accelerate further over the coming century. However, the accelerations observed over century and longer periods2 have not been clearly detected in altimeter data spanning the past two decades. Here we show that the rise, from the sum of all observed contributions to GMSL, increases from 2.2 ± 0.3 mm yr-1 in 1993 to 3.3 ± 0.3 mm yr-1 in 2014. This is in approximate agreement with observed increase in GMSL rise, 2.4 ± 0.2 mm yr-1 (1993) to 2.9 ± 0.3 mm yr-1 (2014), from satellite observations that have been adjusted for small systematic drift, particularly affecting the first decade of satellite observations. 50)
- The mass contributions to GMSL increase from about 50% in 1993 to 70% in 2014 with the largest, and statistically significant, increase coming from the contribution from the Greenland ice sheet, which is less than 5% of the GMSL rate during 1993 but more than 25% during 2014. The suggested acceleration and improved closure of the sea-level budget highlights the importance and urgency of mitigating climate change and formulating coastal adaption plans to mitigate the impacts of ongoing sea-level rise.
Lightning Sparking More Boreal Forest Fires
June 26, 2017: A new NASA-funded study finds that lightning storms were the main driver of recent massive fire years in Alaska and northern Canada, and that these storms are likely to move farther north with climate warming, potentially altering northern landscapes. 51)
The study, led by Vrije Universiteit Amsterdam and the University of California, Irvine, examined the cause of the fires, which have been increasing in number in recent years. There was a record number of lightning-ignited fires in the Canadian Northwest Territories in 2014 and in Alaska in 2015. The team found increases of between two and five percent a year in the number of lightning-ignited fires since 1975. 52)
To study the fires, the team analyzed data from NASA's Terra and Aqua satellites and from ground-based lightning networks.
Lead author Sander Veraverbeke of Vrije Universiteit Amsterdam, who conducted the work while at UC Irvine, said that while the drivers of large fire years in the high north are still poorly understood, the observed trends are consistent with climate change. "We found that it is not just a matter of more burning with higher temperatures. The reality is more complex: higher temperatures also spur more thunderstorms. Lightning from these thunderstorms is what has been igniting many more fires in these recent extreme events," Veraverbeke said.
Study co-author Brendan Rogers at Woods Hole Research Center in Falmouth, Massachusetts, said these trends are likely to continue. "We expect an increasing number of thunderstorms, and hence fires, across the high latitudes in the coming decades as a result of climate change." This is confirmed in the study by different climate model outputs.
Study co-author Charles Miller of NASA's Jet Propulsion Laboratory in Pasadena, California, said while data from the lightning networks were critical to this study, it is challenging to use these data for trend detection because of continuing network upgrades. "A spaceborne sensor that provides high northern latitude lightning data that can be linked with fire dynamics would be a major step forward," he said.
The researchers found that the fires are creeping farther north, near the transition from boreal forests to Arctic tundra. "In these high-latitude ecosystems, permafrost soils store large amounts of carbon that become vulnerable after fires pass through," said co-author James Randerson of the University of California, Irvine. "Exposed mineral soils after tundra fires also provide favorable seedbeds for trees migrating north under a warmer climate."
"Taken together, we discovered a complex feedback loop between climate, lightning, fires, carbon and forests that may quickly alter northern landscapes," Veraverbeke concluded. "A better understanding of these relationships is critical to better predict future influences from climate on fires, and from fires on climate."
Sea Level as a Metronome of Earth's History
May 19, 2017: Sedimentary layers contain stratigraphic cycles and patterns that precisely reveal the succession of climatic and tectonic conditions that have occurred over millennia. Researchers have been working on an analytical method that combines observing deep-water sedimentary strata and measuring in them the isotopic ratio between heavy and light carbon. They have discovered that the cycles that punctuate these sedimentary successions are ascribable to sea level changes. 53) 54) 55)
Sedimentary layers record the history of the Earth. They contain stratigraphic cycles and patterns that precisely reveal the succession of climatic and tectonic conditions that have occurred over millennia, thereby enhancing our ability to understand and predict the evolution of our planet.
Researchers at the University of Geneva (UNIGE), Switzerland, - together with colleagues at the University of Lausanne (UNIL) and American and Spanish scientists - have been working on an analytical method that combines observing deep-water sedimentary strata and measuring in them the isotopic ratio between heavy and light carbon.
They have discovered that the cycles that punctuate these sedimentary successions are not, as one might think, due solely to the erosion of mountains that surround the basin, but are more ascribable to sea level changes. This research, which you can read in the journal Geology, paves the way for new uses of isotopic methods in exploration geology.
The area south of the Pyrenees is particularly suitable for studying sedimentary layers. Rocks are exposed over large distances, allowing researchers to undertake direct observation. Turbidites can be seen here: large sediment deposits formed in the past by underwater avalanches consisting of sand and gravel.
The ups and downs of oceans regulate sedimentation cycles:
The geologists focused their attention on Eocene sedimentary rocks (about 50 million years ago), which was particularly hot, and undertook the isotopic profiling of the sedimentary layers. "We took a sample every 10 meters," says Louis Honegger, a researcher at UNIGE, "measuring the ratio between 13C (heavy carbon stable isotope) and 12C (light carbon stable isotope). The ratio between the two tells us about the amount of organic matter, the main consumer of 12C, which is greater when the sea level is high.
The variations in the ratio helped us explore the possible link with the sea level". The research team found that the turbidite-rich intervals were associated with high 12C levels, and almost always corresponded to periods when the sea level was low. It seems that sedimentary cycles are mainly caused by the rise and fall of the sea level and not by the episodic growth of mountains.
When the sea level is high, continental margins are flooded under a layer of shallow water. Since the rivers are no longer able to flow, they begin to deposit the sediments they carry there. This is why so little material reaches the deep basins downstream. When the sea level is low, however, rivers erode their beds to lower the elevation of their mouth; they transfer their sediment directly to the continental slopes of the deep basins, creating an avalanche of sand and gravel.
Consequently, if the variations of the sea level are known, it is possible to predict the presence of large sedimentary accumulations created by turbidites, which often contain large volumes of hydrocarbons, one of the holy grails of exploration geology.
Measuring stable carbon isotopes: a new indicator of reservoir rocks:
The research provides a new role for the use of carbon isotopes. "From now on, continues Castelltort, we know that by calculating the ratio between 13C and 12C sampled in similar slope deposits close to continents, we can have an indication of the sea level, which means it's possible to better predict the distribution of sedimentary rocks in our subsurface".
In addition, this measurement is relatively simple to perform and it provides accurate data - a real asset for science and mining companies. The study also highlights the importance of sea levels, which are a real metronome for the Earth's sedimentary history.
"Of course," concludes Honegger, "tectonic deformation and erosion are important factors in the formation of sedimentary layers; but they play a secondary role in the formation of turbidite accumulations, which are mainly linked to changes in the sea level".
Ice-shelf Channel Formation in Antarctica
May 15, 2017: A team of scientists led by the ULB (Universite Libre de Bruxelles) Belgium and the Bavarian Academy of Sciences (Munich,Germany) have discovered an active hydrological system of water conduits and sediment ridges below the Antarctic ice sheet. Their study reveals that the scale of these subglacial features is five times bigger than those seen in today's deglaciated landscapes. 56)
The newly discovered, oversized sediment ridges actively shape the ice hundreds kilometers downstream, by carving deep incisions at the bottom of the ice. This is of interest for the stability of the floating ice shelves, as numerous studies show that ice shelf thinning has major consequences for ice sheet stability.
Subglacial conduits form under large ice sheets as part of their basal hydrological system. These tunnels have a typical diameter of several meters to tens of meters, and they funnel the subglacial melt water towards the ocean. However, new geophysical observations by the Laboratoire de Glaciologie of the ULB show that these conduits widen considerably the closer they come to the ocean. A new mathematical model explains this widening with the vanishing overburden pressure at the location where the ice becomes afloat on the ocean.
As the conduits widen, the outflow velocity of the subglacial water decreases, which leads to increased sediment deposition at the conduit's portal. Over thousands of years, this process builds up giant sediment ridges - comparable in height with the Eiffel tower - below the ice. Active sedimentation in subglacial water conduits seems to drive the formations of Eskers - elongated ridges of gravel which are commonly observed today in areas where former ice sheets have retreated. However, the remainders of today's Eskers are considerably smaller in size than those now discovered in Antarctica.
Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. The study team uses ice-penetrating radar data from the Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. The team interprets each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculates that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability. 57)
Water beneath the Antarctic Ice Sheet promotes the formation of ice streams that rapidly slide over wet sediments and a lubricated base. Ice streams discharge the majority of Antarctic ice into floating ice shelves, which surround about 74% of the Antarctic perimeter. Ice shelves occupying embayments buttress the continental mass flux. The buttressing strength depends on the pattern of basal mass balance (i.e., the sum of melting and refreezing), which in turn influences ice-shelf geometry. Measurements show that basal melting is concentrated by ice-shelf channels, which are typically a few kilometers wide and extend for up to hundreds of kilometers along the shelf flow. Ice is thinnest along their central axes (sometimes thinner than half of the ice thickness), and basal melt rates are elevated at their onsets near the grounding line. Theory and satelliteborne observations suggest that such ‘subglacially sourced' ice-shelf channels are formed by buoyant melt-water plumes forced by basal melt water exiting from subglacial conduits at the grounding line. Hitherto, no such conduits have been observed, presumably because they are too small to be detected with ice-penetrating radar.
The study team surveyed three hydrologically predicted subglacial water-outlet locations at the Roi Baudouin Ice Shelf in Dronning Maud Land, Antarctica, all with corresponding ice-shelf channels seawards (Sites A–C, Figure 35a,b). Airborne radar data collected upstream of the satellite-inferred grounding line show distinct radar reflectors situated several hundred meters above the adjacent ice-bed interface (reflectors A–C, Figure 36 c). Using additional ground-based radar data from 2016, the team examined the reflectors' geometry in order to deduce their identity and evaluate three different scenarios for ice-shelf channel formation.
Giant conduits that can sap the ice from below: The evolving sediment ridges leave scars at the bottom of the ice as the ice flows over them. These scars are transmitted to the floating ice shelves farther downstream forming ice-shelf channels. Ice in these channels is up to half as thin as their surroundings, making them a weak spot when exposed to melting from the warmer ocean.
It was originally thought that ice-shelf channels are carved by melting due to the ocean only, but this seems only part of the story: "Our study shows that ice-shelf channels can already be initiated on land, and that the size of the channels significantly depends on sedimentation processes occurring over hundreds to thousands of years" indicates Reinhard Drews, lead author of the study.
The novel link between the subglacial hydrological system, sedimentation, and ice-shelf stability, offers new opportunities to unravel key processes beneath the Antarctic ice sheet, and also improves our ability to reconstruct the ice-sheet extent in the Northern Hemisphere during the last ice ages.
More information on this topic is provided in Ref. 57).
Glacial Lakes Grow in the Himalayas
• May 9, 2017: For people living around the Himalayas, the effects of global warming are anything but distant or abstract. As air temperatures have risen in the past half-century, glaciers have melted and retreated in these mountains. Between 1990 and 2015, Landsat satellites have documented a significant increase in both the number and average size of glacial lakes throughout the range. 58) 59) 60)
- Expanding lakes mean greater risks for the people living in valleys downstream. Specifically, there is a greater risk of GOLFs (Glacial Lake Outburst Floods)—a type of flash flood that occurs when ice or sediment dams collapse beneath glacial lakes. Landslides, avalanches, earthquakes, and volcanic eruptions often trigger GLOFs.
- After analyzing hundreds of satellite images, a research team from the Chinese Academy of Sciences and UCLA (University of California, Los Angeles) concluded that the number of Himalayan glacial lakes increased from 4,459 in 1990 to 4,950 in 2015, with a total area gain of 56 km2, or 14 percent.
- The degree of change varied by region. The size and number of lakes in the southern central Himalayas increased the most, particularly in Nepal, at elevations between 4,200 and 5,800 meters. In the map of Figure 37, regions where lakes expanded the most (20 percent or more) are shown with dark blue; regions where lakes grew only slightly (10 percent or less) are light blue. Lakes in the western Himalayas are generally more stable. Some glaciers in the Karakorum, for instance, are advancing. In contrast, rapid warming in the central Himalayas—as well as more soot being deposited on ice—may explain the rapid retreat of glaciers there.
- The researchers observed changes to lakes at both the terminus of glaciers (proglacial lakes) and on top of them (supraglacial lakes). Between 1990 and 2015, the number of proglacial lakes increased by 227; the number of supraglacial lakes rose by 144. About 81 percent of the expansion in lake area was caused by changes to proglacial lakes.
- The researchers also identified 118 proglacial lakes that pose a particularly high risk to people living downstream. These lakes—many of them in the central Himalayas near Kathmandu, Nepal, and in the eastern Himalayas near Thimphu, Bhutan—grew by more than 1 percent each year.
- One rapidly expanding proglacial lake, Cirenmaco, highlights the risks. It stands at the base of Amaciren Glacier in the Zhangzangbo Valley of Nepal, and it was the scene of outburst floods in 1964 and 1981. The flood in 1981 was particularly destructive, killing hundreds of people, knocking out a power plant, and destroying bridges and roads. As seen in the false-color Landsat images (Figure 38), Cirenmaco's size more than doubled between 1988 and 2015.
- While proglacial lakes generally grew steadily each year, the lakes emerging on top of the glaciers were small, short-lived, and fast-changing. Many supraglacial lakes are perched on debris-covered ice, meaning lake water can quickly drain deeper into the glacier when cracks emerge.
- Nepal's Ngozumpa Glacier (Figure 39), which lies about 25 km west of Mount Everest, has seen a significant increase in the number and size of supraglacial lakes on its surface. The pair of Landsat images below show the surface of the glacier in 1989 and 2015. Many of the lakes that existed in 1990 had drained by 2015, while many new lakes emerged in other areas.
- Researchers point to rising temperatures and melting glaciers as the primary cause for the increase in the size and number of lakes in the Himalayas. Rates of warming vary by region, but match the increases in total lake area. For instance, the team noted that between 1979 and 2014, temperatures rose by 5.9ºC at Nyalam in the central Himalaya; 1.0 ºC at Shiquanhe in the western Himalaya; and 0.4ºC at Yadong in the eastern Himalaya.
- "As the region continues to warm, it is urgent that scientists continue to monitor the most rapidly expanding glacial lakes with satellites because many are remote and very difficult to access," said Yong Nie, lead author of the study. "If we know which lakes pose the greatest risk, then authorities can take steps to develop early warning systems, drain specific high-risk lakes, and educate people on how to minimize their exposure to flash floods."
- Yongwei Sheng, a geography professor at UCLA and one of the study authors, added: "While we have reported on widespread lake expansion across the Himalayas, region-specific driving mechanisms, lake-specific risk assessments, as well as future change prediction all deserve further investigation."
Regional Sea Level Scenarios for Coastal Risk Management
• May 2017: Sea level rise is occurring worldwide, but not at the same rate everywhere. Differences will also likely continue in the future, so decision-makers need local information to assess their community's vulnerability. These new scenarios integrate updated global sea level rise scenarios with regional factors, such as changes in land elevations and ocean circulation, that influence sea level regionally.
"The ocean is not rising like water would in a bathtub," said William Sweet, a NOAA oceanographer and lead author of the report detailing the scenarios. "For example, in some scenarios sea levels in the Pacific Northwest are expected to rise slower than the global average, but in the Northeast they are expected to rise faster. These scenarios will help communities better understand local trends and make decisions about adaptation that are best for them." 61) 62)
In the USA, the "Sea Level Rise and Coastal Flood Hazard Scenarios and Tools Interagency Task Force", jointly convened by the USGCRP (U.S. Global Change Research Program) and the NOC (National Ocean Council), began its work in August 2015. The Task Force has focused its efforts on three primary tasks: 1) updating scenarios of GMSL (Global Mean Sea Level) rise, 2) integrating the global scenarios with regional factors contributing to sea level change for the entire U.S. coastline, and 3) incorporating these regionally appropriate scenarios within coastal risk management tools and capabilities deployed by individual agencies in support of the needs of specific stakeholder groups and user communities.
Long-term sea level rise driven by global climate change presents clear and highly consequential risks to the United States over the coming decades and centuries. Today, millions of people in the United States already live in areas at risk of coastal flooding, with more moving to the coasts every year . Rising seas will dramatically increase the vulnerability of this growing population, along with critical infrastructure related to transportation, energy, trade, military readiness, and coastal ecosystems and the supporting services they provide.
GMSL (Global Mean Sea Level) has increased by about 21 cm to 24 cm since 1880, with about 8 cm occurring since 1993. In addition, the rate of GMSL rise since 1900 has been faster than during any comparable period over at least the last 2800 years. Scientists expect that GMSL will continue to rise throughout the 21st century and beyond, because of global warming that has already occurred and warming that is yet to occur due to the still-uncertain level of future emissions. GMSL rise is a certain impact of climate change; the questions are when, and how much, rather than if. There is also a long-term commitment (persistent trend); even if society sharply reduces emissions in the coming decades, sea level will most likely continue to rise for centuries.
While the long-term, upward shift in sea level is an underlying driver of changes to the nation's coasts, impacts are generally expressed through extreme water levels (short-period, lower-probability events both chronic and acute in nature) occurring against the background of this shifting baseline. Higher sea levels worsen the impacts of storm surge, high tides, and wave action, even absent any changes in storm frequency and intensity. Even the relatively small increases in sea level over the last several decades have led to greater storm impacts at many places along the U.S. coast. Similarly, the frequency of intermittent flooding associated with unusually high tides has increased rapidly (accelerating in many locations) in response to increases in RSL (Relative Sea Level ) as shown in Figure 40. At some locations in the United States, the frequency of tidal flooding (events typically without a local storm present) has increased by an order of magnitude over the past several decades, turning it from a rare event into a recurrent and disruptive problem. Significant, direct impacts of long-term RSL rise, including loss of life, damage to infrastructure and the built environment, permanent loss of land, ecological regime shifts in coastal wetlands and estuary systems, and water quality impairment, also occur when key thresholds in the coastal environment are crossed. Some of these impacts have the potential to ‘feedback' and influence wave impacts and coastal flooding. For example, there is evidence that wave action and flooding of beaches and marshes can induce changes in coastal geomorphology, such as sediment build up, that may iteratively modify the future flood risk profile of communities and ecosystems.
In this context, there is a clear need—and a clear call from states and coastal communities (White House, 2014)—to support preparedness planning with consistent, accessible, authoritative and more locally appropriate knowledge, data, information, and tools about future changes in sea level and associated coastal risks. In response to this need, the White House Council on Climate Preparedness and Resilience in 2015 called for the establishment of the Federal Interagency Sea Level Rise and Coastal Flood Hazard Scenarios and Tools Task Force, a joint task force of the NOC (National Ocean Council) and the USGCRP (U.S. Global Change Research Program ). The Task Force's charge is to develop and disseminate, through interagency coordination and collaboration, future RSL and associated coastal flood hazard scenarios and tools for the entire United States. These scenarios and tools are intended to serve as a starting point for on-the-ground coastal preparedness planning and risk management processes, including compliance with the new FFRMS (Federal Flood Risk Management Standard).
The Task Force is charged with leveraging the best available science; incorporating regional science and expertise where appropriate; building this information into user-friendly mapping, visualization, and analysis tools; and making it easily accessible through established Federal web portals. Part of the motivation for forming the Task Force was to bring together key efforts within individual agencies, such as the FEMA (Federal Emergency Management Agency), NOAA (National Oceanic and Atmospheric Administration), USACE (U.S. Army Corps of Engineers), USGS (U.S. Geological Survey), DoD (Department of Defense), EPA (Environmental Protection Agency) and NASA (National Aeronautics and Space Administration), that could serve as building blocks of an overall Federal system of sea level information and decision support, and to provide synthesis and coverage of the entire United States coastline.
• May 4, 2017: Thanks in large part to satellite measurements, scientists' skill in measuring how much sea levels are rising on a global scale - currently 3.4 mm per year - has improved dramatically over the past quarter century. But at the local level, it's been harder to estimate specific regional sea level changes 10 or 20 years away - the critical timeframe for regional planners and decision makers. 63)
That's because sea level changes for many reasons, on differing timescales, and is not the same from one place to the next. Developing more accurate regional forecasts of sea level rise will therefore have far-reaching benefits for the more than 30 percent of Americans who currently reside along the Pacific, Atlantic or Gulf Coasts of the contiguous United States.
New research published this week in the Journal of Climate reveals that one key measurement — large-scale upper-ocean temperature changes caused by natural cycles of the ocean — is a good indicator of regional coastal sea level changes on these decadal timescales. Such data may give planners and decision makers a new tool to identify key regions of U.S. coastlines that may be vulnerable to sea level changes on 10- to 20-year timescales. 64)
"Decision makers need a diverse set of tools with different informational needs," said lead author Veronica Nieves of UCLA and NASA's Jet Propulsion Laboratory in Pasadena, California. "Having a better understanding of the chances of local flood damage from rising seas in coastal areas is a key factor in being able to assess vulnerability, risk and adaptation options." Such tools could help planners decide whether a given part of a coastline would be better served by "soft" techniques, such as beach replenishment or preservation of wetlands, or by "hard" techniques, such as construction of sea walls or levees.
Nieves' team, which included participation from the IMEDEA (Mediterranean Institute for Advanced Studies) in Esporles, Spain, set out to detect decadal sea level changes over large U.S. coastal ocean regions. They compared existing NOAA records of upper-ocean temperatures in coastal waters for each U.S. ocean coastline with records of actual sea level changes from 1955 to 2012, and data from U.S./European satellite altimeter missions since 1992. They identified those sea level changes that have a large impact at regional scales in many locations, including largely populated cities. Sea level along the U.S. East Coast and West Coast can rise and fall by an inch or two (several centimeters) over the course of a decade or two because of fluctuations in upper ocean temperatures.
Their method was able to explain about 70 percent of regional sea level variability on decadal time scales for the West Coast, about 80 percent for the East Coast, and about 45 percent for the Gulf Coast. Along the Gulf Coast, the authors say other factors, such as tidal effects and the ongoing subsidence, or sinking, of the land, can play a more important role.
"Our study shows that large-scale upper-ocean temperature changes provide a good way to distinguish decade-long natural ocean signals from longer-term global warming signals," said Nieves. "This is important for regional planning, because it allows policymakers to identify places where climate change dominates the observed sea level rise and places where the climate change signal is masked by shorter-term regional variability caused by natural ocean climate cycles."
Nieves said an example is the U.S. West Coast, where the phase of a multi-decadal ocean climate pattern, called the Pacific Decadal Oscillation, has helped keep sea level rise lower during the past two decades. With the recent shift of this oscillation to its opposite phase, scientists expect sea level rise along the West Coast to accelerate in coming years.
"Scientists have worked hard to understand the really fast changes in sea level, such as storm surges, because they cause major damage, and the really slow changes because long-term sea level rise will shape the coastlines of the future," said study co-author Josh Willis of JPL. "But in between these fast and slow changes, there's a gap in our understanding. The results of our study help fill that gap."
Sea Ice Extent Sinks to Record Lows at Both Poles
• March 22, 2017: Arctic sea ice appears to have reached on March 7 a record low wintertime maximum extent, according to scientists at NASA and the NASA-supported NSIDC (National Snow and Ice Data Center ) in Boulder, Colorado. And on the opposite side of the planet, on March 3 sea ice around Antarctica hit its lowest extent ever recorded by satellites at the end of summer in the Southern Hemisphere, a surprising turn of events after decades of moderate sea ice expansion. 65) 66) 67)
On Feb. 13, 2017, the combined Arctic and Antarctic sea ice numbers were at their lowest point since satellites began to continuously measure sea ice in 1979. Total polar sea ice covered 16.21 million km2, which is 2 million km2 less than the average global minimum extent for 1981-2010 – the equivalent of having lost a chunk of sea ice larger than Mexico.
The ice floating on top of the Arctic Ocean and surrounding seas shrinks in a seasonal cycle from mid-March until mid-September. As the Arctic temperatures drop in the autumn and winter, the ice cover grows again until it reaches its yearly maximum extent, typically in March. The ring of sea ice around the Antarctic continent behaves in a similar manner, with the calendar flipped: it usually reaches its maximum in September and its minimum in February.
This winter, a combination of warmer-than-average temperatures, winds unfavorable to ice expansion, and a series of storms halted sea ice growth in the Arctic. This year's maximum extent, reached on March 7 at 14.42 million km2, is 96,000 km2 below the previous record low, which occurred in 2015, and 1.22 million km2 smaller than the average maximum extent for 1981-2010.
"We started from a low September minimum extent," said Walt Meier, a sea ice scientist at NASA/GSFC in Greenbelt, Maryland. "There was a lot of open ocean water and we saw periods of very slow ice growth in late October and into November, because the water had a lot of accumulated heat that had to be dissipated before ice could grow. The ice formation got a late start and everything lagged behind – it was hard for the sea ice cover to catch up."
The Arctic's sea ice maximum extent has dropped by an average of 2.8 % per decade since 1979. The summertime minimum extent losses are nearly five times larger: 13.5% per decade. Besides shrinking in extent, the sea ice cap is also thinning and becoming more vulnerable to the action of ocean waters, winds and warmer temperatures.
This year's record low sea ice maximum extent might not necessarily lead to a new record low summertime minimum extent, since weather has a great impact on the melt season's outcome, Meier said. "But it's guaranteed to be below normal."
In Antarctica, this year's record low annual sea ice minimum of 2.11 million km2 was 184,000 km2 below the previous lowest minimum extent in the satellite record, which occurred in 1997.
Antarctic sea ice saw an early maximum extent in 2016, followed by a very rapid loss of ice starting in early September. Since November, the daily Antarctic sea ice extent has continuously been at its lowest levels in the satellite record. The ice loss slowed down in February.
This year's record low happened just two years after several monthly record high sea ice extents in Antarctica and decades of moderate sea ice growth. "There's a lot of year-to-year variability in both Arctic and Antarctic sea ice, but overall, until last year, the trends in the Antarctic for every single month were toward more sea ice," said Claire Parkinson, a senior sea ice researcher at Goddard. "Last year was stunningly different, with prominent sea ice decreases in the Antarctic. To think that now the Antarctic sea ice extent is actually reaching a record minimum, that's definitely of interest."
"It is tempting to say that the record low we are seeing this year is global warming finally catching up with Antarctica," Meier said. "However, this might just be an extreme case of pushing the envelope of year-to-year variability. We'll need to have several more years of data to be able to say there has been a significant change in the trend."
2016 Warmest Year on Record Globally
• January 18, 2017: Earth's 2016 surface temperatures were the warmest since modern record-keeping began in 1880, according to independent analyses by NASA and NOAA (National Oceanic and Atmospheric Administration). Globally-averaged temperatures in 2016 were 0.99 degrees Celsius warmer than the mid-20th century mean. This makes 2016 the third year in a row to set a new record for global average surface temperatures. 68)
The 2016 temperatures continue a long-term warming trend, according to analyses by scientists at NASA/GISS ( Goddard Institute for Space Studies) in New York. NOAA scientists concur with the finding that 2016 was the warmest year on record based on separate, independent analyses of the data.
Because weather station locations and measurement practices change over time, there are uncertainties in the interpretation of specific year-to-year global mean temperature differences. However, even taking this into account, NASA estimates 2016 was the warmest year with greater than 95 percent certainty. "2016 is remarkably the third record year in a row in this series," said GISS Director Gavin Schmidt. "We don't expect record years every year, but the ongoing long-term warming trend is clear." The planet's average surface temperature has risen about 1.1 degrees Celsius since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere.
Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001. Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year – from January through September, with the exception of June – were the warmest on record for those respective months. October, November, and December of 2016 were the second warmest of those months on record – in all three cases, behind records set in 2015.
Phenomena such as El Niño or La Niña, which warm or cool the upper tropical Pacific Ocean and cause corresponding variations in global wind and weather patterns, contribute to short-term variations in global average temperature. A warming El Niño event was in effect for most of 2015 and the first third of 2016. Researchers estimate the direct impact of the natural El Niño warming in the tropical Pacific increased the annual global temperature anomaly for 2016 by 0.12 degrees Celsius.
Weather dynamics often affect regional temperatures, so not every region on Earth experienced record average temperatures last year. For example, both NASA and NOAA found the 2016 annual mean temperature for the contiguous 48 United States was the second warmest on record. In contrast, the Arctic experienced its warmest year ever, consistent with record low sea ice found in that region for most of the year.
NASA's analyses incorporate surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions. The result of these calculations is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.
NOAA scientists used much of the same raw temperature data, but with a different baseline period, and different methods to analyze Earth's polar regions and global temperatures.
GISS is a laboratory within the Earth Sciences Division of NASA's Goddard Space Flight Center in Greenbelt, Maryland. The laboratory is affiliated with Columbia University's Earth Institute and School of Engineering and Applied Science in New York.
Changing Rainfall Patterns Linked to Water Security in India
• January 11, 2017: Changing rainfall is the key factor driving changes in groundwater storage in India, according to a new study led by the IIT (Indian Institute of Technology) Gandhinagar published in the journal Nature Geoscience. The study shows that changing monsoon patterns - which are tied to higher temperatures in the Indian Ocean - are an even greater driver of change in groundwater storage than the pumping of groundwater for agriculture. 69) 70)
Agriculture in India relies heavily on groundwater for irrigation, particularly in the dry northern regions where precipitation is scarce. Groundwater withdrawals in the country have increased over tenfold since the 1950's, from 10-20 km3 per year in 1950, to 240-260 km3 per year in 2009. And satellite measurements have shown major declines in groundwater storage in some parts of the country, particularly in northern India.
"Groundwater plays a vital role in food and water security in India. Sustainable use of groundwater resources for irrigation is the key for future food grain production," says study leader Vimal Mishra, of the IIT Gandhinagar. "And with a fast-growing population, managing groundwater sustainably is going become even more important. The linkage between monsoon rainfall and groundwater can suggest ways to enhance groundwater recharge in India and especially in the regions where rainfall has been declining, such as the Indo-Gangetic Plain."
Groundwater acts like a bank for water storage, receiving deposits from surface water and precipitation, and withdrawals as people pump out water for drinking, industry, and irrigating fields. If withdrawals add up to more than the deposits, eventually the accounts could run dry, which could have disastrous consequences.
"This study adds another dimension to the existing water management framework. We need to consider not just the withdrawals, but also the deposits in the system," says Yoshihide Wada, a study coauthor and the deputy director of the Water program at the IIASA (International Institute for Applied Systems Analysis) in Austria.
The issue of groundwater depletion has been a topic of much discussion in India, but most planning has focused on pumping, or the demand side, rather than the deposit side. By looking at water levels in wells around the country, the researchers could track groundwater replenishment following the monsoons. They found that in fact, variability in the monsoons is the key factor driving the changing groundwater storage levels across the country, even as withdrawals increase.
In addition, the researchers found that the monsoon precipitation is correlated with Indian Ocean temperature, a finding which could potentially help to improve precipitation forecasts and aid in water resource planning.
"Weather is uncertain by nature, and the impacts of climate change are extremely difficult to predict at a regional level," says Wada "But our research suggests that we must focus more attention on this side of the equation if we want to sustainably manage water resources for the future."
Ozone Hole 2016, and a Historic Climate Agreement
• October 27, 2016: The size and depth of the ozone hole over Antarctica was not remarkable in 2016. As expected, ozone levels have stabilized, but full recovery is still decades away. What is remarkable is that the same international agreement that successfully put the ozone layer on the road to recovery is now being used to address climate change. 71)
The stratospheric ozone layer protects life on Earth by absorbing ultraviolet light, which damages DNA in plants and animals (including humans) and leads to health issues like skin cancer. Prior to 1979, scientists had never observed ozone concentrations below 220 Dobson Units. But in the early 1980s, through a combination of ground-based and satellite measurements, scientists began to realize that Earth's natural sunscreen was thinning dramatically over the South Pole. This large, thin spot in the ozone layer each southern spring came to be known as the ozone hole.
The image of Figure 49 shows the Antarctic ozone hole on October 1, 2016, as observed by the OMI (Ozone Monitoring Instrument) on NASA's Aura satellite. On that day, the ozone layer reached its average annual minimum concentration, which measured 114 Dobson Units. For comparison, the ozone layer in 2015 reached a minimum of 101 Dobson Units. During the 1960s, long before the Antarctic ozone hole occurred, average ozone concentrations above the South Pole ranged from 260 to 320 Dobson Units.
The area of the ozone hole in 2016 peaked on September 28, 2016, at about 23 million km2. "This year we saw an ozone hole that was just below average size," said Paul Newman, ozone expert and chief scientist for Earth Science at NASA's Goddard Space Flight Center. "What we're seeing is consistent with our expectation and our understanding of ozone depletion chemistry and stratospheric weather."
The image of Figure 50 was acquired on October 2 by the OMPS (Ozone Mapping Profiler Suite) instrumentation during a single orbit of the Suomi-NPP satellite. It reveals the density of ozone at various altitudes, with dark orange areas having more ozone and light orange areas having less. Notice that the word hole isn't literal; ozone is still present over Antarctica, but it is thinner and less dense in some areas.
In 2014, an assessment by 282 scientists from 36 countries found that the ozone layer is on track for recovery within the next few decades. Ozone-depleting chemicals such as chlorofluorocarbons (CFCs)—which were once used for refrigerants, aerosol spray cans, insulation foam, and fire suppression—were phased out years ago. The existing CFCs in the stratosphere will take many years to decay, but if nations continue to follow the guidelines of the Montreal Protocol, global ozone levels should recover to 1980 levels by 2050 and the ozone hole over Antarctica should recover by 2070.
The replacement of CFCs with hydrofluorocarbons (HFCs) during the past decade has saved the ozone layer but created a new problem for climate change. HFCs are potent greenhouse gases, and their use — particularly in refrigeration and air conditioning — has been quickly increasing around the world. The HFC problem was recently on the agenda at a United Nations meeting in Kigali, Rwanda. On October 15, 2016, a new amendment greatly expanded the Montreal Protocol by targeting HFCs, the so-called "grandchildren" of the Montreal Protocol.
"The Montreal Protocol is written so that we can control ozone-depleting substances and their replacements," said Paul Newman, who participated in the meeting in Kigali. "This agreement is a huge step forward because it is essentially the first real climate mitigation treaty that has bite to it. It has strict obligations for bringing down HFCs, and is forcing scientists and engineers to look for alternatives."
NASA Releases First Map of Thawed Areas under Greenland's Ice Sheet
• August 2016: NASA researchers have helped produce the first map showing what parts of the bottom of the massive Greenland Ice Sheet are thawed – key information in better predicting how the ice sheet will react to a warming climate. 72)
Greenland's thick ice sheet insulates the bedrock below from the cold temperatures at the surface, so the bottom of the ice is often tens of degrees warmer than at the top, because the ice bottom is slowly warmed by heat coming from the Earth's depths. Knowing whether Greenland's ice lies on wet, slippery ground or is anchored to dry, frozen bedrock is essential for predicting how this ice will flow in the future, But scientists have very few direct observations of the thermal conditions beneath the ice sheet, obtained through fewer than two dozen boreholes that have reached the bottom. Now, a new study synthesizes several methods to infer the Greenland Ice Sheet's basal thermal state –whether the bottom of the ice is melted or not– leading to the first map that identifies frozen and thawed areas across the whole ice sheet.
"We're ultimately interested in understanding how the ice sheet flows and how it will behave in the future," said Joe MacGregor, lead author of the study and a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Md. "If the ice at its bottom is at the melting point temperature, or thawed, then there could be enough liquid water there for the ice to flow faster and affect how quickly it responds to climate change."
For this study, published last month in the Journal of Geophysical Research – Earth Surface, MacGregor's team combined four different approaches to investigate the basal thermal state. First, they examined results from eight recent computer models of the ice sheet, which predict bottom temperatures. Second, they studied the layers that compose the ice sheet itself, which are detected by radars onboard NASA's Operation IceBridge aircraft and suggest where the bottom of the ice is melting rapidly. Third, they looked at where the ice surface speed measured by satellites exceeds its "speed limit", the maximum velocity at which the ice could flow and still be frozen to the rock beneath it. Fourth, they studied imagery from the MODIS (Moderate Resolution Imaging Spectroradiometers) on the NASA Terra and Aqua satellites looking for rugged surface terrain that is usually indicative of ice sliding over a thawed bed. 73)
"Each of these methods has strengths and weaknesses. Considering just one isn't enough. By combining them, we produced the first large-scale assessment of Greenland's basal thermal state," MacGregor said. For each method, MacGregor's team looked for areas where the technique confidently inferred that the bed of Greenland's ice sheet was thawed or frozen. They then looked at the places where these methods agreed and classified these areas as likely thawed or likely frozen. The zones where there was insufficient data or the methods disagreed, they classified as uncertain.
From this synthesis, MacGregor and his colleagues determined that the bed is likely thawed under Greenland's southwestern and northeastern ice drainages, while it's frozen in the interior and west of the ice sheet's central ice divide. For a third of the Greenland ice sheet, there's not enough data available to determine its basal thermal state.
MacGregor said the team's map (Figure 51) is just one step in fully assessing the thermal state of the bottom of Greenland's ice sheet. "I call this the piñata, because it's a first assessment that is bound to get beat up by other groups as techniques improve or new data are introduced. But that still makes our effort essential, because prior to our study, we had little to pick on."
Hazardous Thunderstorm Intensification Over Lake Victoria
• Sept. 22, 2016: An international study has determined that Lake Victoria in East Africa will become a hotspot for hazardous thunderstorms due to climate change using techniques that could improve regional climate and weather forecasts around inland bodies of water in the United States. 74)
Lake Victoria is divided among Uganda, Kenya and Tanzania. With a surface area close to 70,000 km2, it is the biggest lake in Africa. The lake is also a notoriously dangerous place for the 200,000 people who go fishing there at night. The International Red Cross estimates that between 3,000 and 5,000 fishermen per year lose their lives in violent storms on the lake.
Climate scientist Wim Thiery, affiliated with KU Leuven (Catholic University of Leuven, Belgium) and ETH Zürich (Swiss Federal Institute of Technology in Zürich, Switzerland), was able provide scientific evidence for why the storms occur in collaboration with colleague Kristopher Bedka of NASA's Langley Research Center in Hampton, Virginia.
"Thanks to new satellite-based storm detection products developed at NASA, we were able to map the number of hazardous thunderstorms and their locations in East Africa – every 15 minutes for a period ranging from 2005 to 2013," Thiery said. "During the day, most storms rage over the surrounding land, especially the typical afternoon thunderstorms that are caused by local upsurges of warm air. At night, these storms concentrate above Lake Victoria."
The storms are caused by circulation in the atmosphere above Victoria's enormous surface, according to Thiery. Daytime breezes flow outward from the cool water toward the warm land. At night, the opposite happens. Land breezes converge over the lake. Add in evaporation and you end up with storms.
To predict the impact of climate change on this process, Thiery ran climate simulations using an advanced computer model and determined that if the emission of greenhouse gases continues to increase, the extreme amounts of rainfall over Lake Victoria will increase by twice as much as the rainfall over the surrounding land. As a result, the lake will become a hotspot for night-time storms. "We found out that it is crucial to run our climate model at high resolution, and to couple a lake model to our climate model," Thiery said. "Resolving the lakes and getting lake surface temperatures right in the model is crucial to predicting the impact of these lakes on the regional climate and to get better projections of climate change."
The same advanced computer modeling could be useful in predicting future impacts of climate change around inland bodies of water in the U.S. "When performing climate simulations, it is very important to allow the body of water to accurately modify the atmosphere around it and vice versa," said Bedka, a climate scientist at NASA Langley. "Lakes and wide rivers such as Lake Michigan, the Mississippi River and, locally, the James River generate air circulations that can impact where thunderstorms form over the surrounding land. If climate projections do not properly account for these detailed interactions between land and water, they will underestimate their impact."
Properly coupled high-resolution models would be especially useful if these bodies of water were to warm up by a few degrees. That warming would have an impact on regional climate, and without precise modeling that impact could be difficult to predict and mitigate.
In addition, the satellite-based storm detection products that were crucial to the Lake Victoria study could also be useful in the U.S. Bedka and his team at NASA developed methods to automatically identify hazardous thunderstorms in "any satellite image, anytime, anywhere across the world." Lengthy datasets drawn from those methods could be used in the U.S. to help uncover interactions between land and water with a great degree of clarity.
Satellite data analysis: Satellite observations enable the recognition of severe weather by detecting OTs (Overshooting Tops) , that is, dome-like protrusions atop a cumulonimbus anvil induced by intense updrafts. OTs mark the presence of vigorous thunderstorms and are tightly linked to severe weather reports. By applying an OT detection algorithm to Methods (Meteosat Second Generation observations), the team established a new severe thunderstorm climatology for East Africa. The results reveal a marked imprint of Lake Victoria on the diurnal thunderstorm cycle and confirm its status as one of the most convectively active regions on Earth (Figure 52). From 2005 to 2013, 73% of all 1,400,000 OT pixels detected over the lake occurred at night (22:00 to 9:00 UTC), in contrast to the surrounding land where afternoon storms dominate (72% of all 4,200,000 OT pixels during 9:00 to 16:00 UTC). Local evaporation and mesoscale circulation have been identified as key drivers of the present-day diurnal cycle of precipitation over Lake Victoria, but so far it is not known how mean and extreme precipitation over this lake respond to a temperature increase induced by anthropogenic greenhouse gas emissions. To address this question, the team performed a high resolution (~7 km grid spacing), coupled lake–land–atmosphere climate projection for the African Great Lakes region with the regional climate model COSMO/CLM2 (Consortium for Small-scale Modeling/Community Land Model2), and analyzed coarser-scale ensemble projections from CORDEX (Coordinated Regional climate Downscaling Experiment) for the end of the century under a high-emission scenario. 75)
Extreme precipitation projections: The projections show a contrasting change of mean and extreme precipitation over Lake Victoria (Figure 53), with mean precipitation decreasing while the intensity of extreme precipitation increases. Moreover, by the end of the century the increase in extremes (precipitation above the 99th percentile) is 2.4±0.1 times higher over the lake than over its surrounding land in the highresolution projection (1.8±1.0 times in the CORDEX ensemble). Today convection initiates in the eastern part of the lake and intensifies while being advected westwards along the trade winds. In the future, storms are projected to release extreme precipitation more in the eastern part of the lake, leading to an eastward shift of intense precipitation (Figure 53a,b).
The results emphasize a major hazard associated with climate change over East Africa with potential severe human impacts. Lake Victoria directly sustains the livelihood of 30 million people living at its coasts and its fishing industry is a leading natural resource for East African communities. However, given the projected increase in extreme over-lake thunderstorms, the current vulnerability of local fishing communities and their growing exposure driven by rapid urbanization along the lakefront, this lake is likely to remain the most dangerous stretch of water in the world. At the same time, the findings mark an opportunity for developing a satellite-based early warning system for hazardous thunderstorms over Lake Victoria.
Climate Change Already Accelerating Sea Level Rise
• August 10, 2016: Greenhouse gases are already having an accelerating effect on sea level rise, but the impact has so far been masked by the cataclysmic 1991 eruption of Mount Pinatubo in the Philippines, according to a new study led by NCAR (National Center for Atmospheric Research), Boulder, CO. 76) 77)
Driven by both the warming of the oceans and mass loss of the cryosphere,GSML (Global Mean Sea Level) is among the most powerful indicators of a changing climate. Originally estimated from a network of tide gages and restricted to coastlines, it has been derived from satellite measurements over the ice-free oceans since shortly after the launch of the TOPEX/Poseidon satellite in late 1992 with unprecedented accuracy and stability. During a given year, the height of the global seas can now be estimated to within a few millimeters revealing a mean rise of just over 3 mm yr-1. However the holistic nature of sea level has also led to challenges in its interpretation and it can be unclear at times whether its variations arise from changes in ocean heating, cryospheric melting, or the amount of water stored over land. Disentangling these various influences remains an ongoing science objective.
Among the major unanswered questions is why GMSL acceleration has not yet been detected in the altimeter record, given the increasing rates at which glacial and ice sheet melt are estimated to have occurred and as greenhouse gas concentrations have risen. The answer to this question has considerable policy relevance and debates over whether such an expected acceleration should be considered at the local policy level have at times been contentious. GMSL also has the potential to serve as an early indicator of accelerated climate change as it is less sensitive to the large internal variability that characterizes the surface temperature record, as evidenced by the recent so-called hiatus in global warming. Prevailing hypotheses for the lack of observed acceleration have maintained that changes in water storage over land or even drift in the satellite instruments may be to blame. Here it is demonstrated that the environment in which the era began was itself highly anomalous due to the preceding eruption of Mt Pinatubo on June 15, 1991, which cooled the oceans and decreased water storage over land and in the atmosphere. The net effect of these changes was to lower sea level prior to the altimeter era and induce an anomalous rise in the era's early years. It is proposed that this early anomalous rise masked the acceleration that would have otherwise occurred in the broader record. A consequence of this interpretation is that as the altimeter record lengthens, and in the coming decade barring another major volcanic eruption, accelerated rise will likely be detected.
Since late 1992 until the present, the TOPEX/Poseidon (T/P), Jason-1, and Jason-2 satellite altimeter missions have continuously measured sea level changes between ± 66º latitude with a temporal resolution of about 10 days, as shown in Figure 54. With their precision orbit determination, dual-frequency measurements (to remove ionosphere delays) and microwave radiometer (to remove delays due to water vapor in the troposphere), these missions have created an unrivaled 23-year climate data record of sea level change that is now being extended with the successful launch and deployment of the Jason-3 satellite earlier this year. Great care has been taken in calibrating these measurements via overlaps between missions and comparison to tide gauge sea level data. When averaged globally, the record provides an estimate of GMSL with a seasonal mean accuracy of 1–2 mm2.
Over the 23-year time series, it shows that GMSL has been rising at a rate of 3.3 ± 0.4 mm yr-1, but with notable inter-decadal variability.The current best estimate of the rates during the first (1993–2002) and second (2003– 2012) decades of the altimeter era are 3.5 and 2.7 mm yr-1, respectively, though important sources of uncertainty persist and raise caution regarding the record's early years (dashed line, Figure 54). There are several theories to explain this variability, but here we present an additional explanation, with important implications for anticipated near-future acceleration.
Legend to Figure 54: Estimates during the early stages of the record (dashed) are particularly subject to instrument related uncertainty.
Insight from Tide Gages: Prior to satellite altimetry, the primary source of sea level data is from historical tide gage records. These data provide a significantly longer time series relative to that of satellite altimetry, with a few records extending back into the 18th century. Several studies have estimated GMSL from the tide gage record using a variety of techniques. The resulting estimates of the GMSL trend from 1900 to 1990 range from 1.2 mm yr-1 to 1.9 mm yr-1, albeit with significant decadal variability about this long-term trend. Coupled with the higher GMSL trend observed during the satellite altimeter record discussed above, the tide gage record demonstrates unequivocal acceleration since the early 1900 s, with estimates ranging from 0.009 ± 0.002 mm yr-2 to 0.017 ± 0.003 mm yr-2. Based on these same studies, however, the majority of the acceleration arises from a shift that occurs around 1990 when the rate of sea level rise increases to the satellite-measured trend of 3.3 mm yr-1.
While the tide gage record may provide a ballpark estimate for what to expect during the altimeter era, it provides only weak quantitative information regarding what acceleration should be expected. In practice, calculating GMSL from 1900 to the present is a challenging problem based on the spatial and temporal sampling characteristics of available gages. There is little consensus across tide gage studies on the rate and acceleration of GMSL over the past century, thus making it difficult to interpret the altimeter era in a broader context. As an alternative approach to understanding sea level variability, we therefore seek to estimate and remove effects that obscure a possible underlying acceleration from the altimeter record itself. By doing so, we can potentially estimate the acceleration in GMSL directly from altimetry.
The GMSL Influence of the 1991 Mt Pinatubo Eruption: On June 15, 1991 the second largest volcanic eruption of the twentieth century in terms of aerosol radiative forcing began on the Philippine island of Luzon. Estimates of the amount of ash deposited in the stratosphere ranged from 20 to 30 Tg21 (approximately equal to a tenth the mass of all mankind) inducing a cooling of the globe and especially the world's oceans. Model-based estimates of the eruption's cooling effects suggest that the recovery of ocean heat content during the 1990's may have increased sea level rise by as much as 0.5 mm yr-1 on average in the decade following the eruption. The precise temporal evolution of the increase, and the impacts of the eruption on terrestrial and atmospheric water reservoirs remain largely unknown however; as quantifying these impacts is complicated by contemporaneous climate variability that can mask or amplify the response. Moreover, as many of the tools now in place for monitoring climate, such as for example the ARGO network of ocean temperature sensors and the GRACE satellite for estimating terrestrial water storage, were yet to be deployed at the time of the eruption, quantifying its precise climatic effects is nontrivial. However, recent specially designed climate model experiments now provide additional insight. What they reveal is that the eruption had a profound and temporally complex influence on several contributors to sea level and especially the amount of heat stored in the oceans, even when compared to background variations in climate, with major consequences for perceptions of GMSL acceleration during the altimeter era.
The CESM (Community Earth System Model) LE (Large Ensemble) is a 40-member ensemble of state-of-the-art coupled climate simulations spanning the 20th and 21st centuries using estimated historical forcings including volcanic eruptions. The simulated responses of GMSL and its individual contributors to the 1991 eruption of Mt Pinatubo are summarized in Figure 55. Immediately following the eruption, aerosols in the stratosphere blocked sunlight and cooled the surface. Surface temperatures quickly dropped, particularly over land due to its relative lack of thermal inertia. In turn, the atmosphere cooled, reducing the amount of moisture stored within it as water vapor. A cooler surface evaporated less moisture and was less convectively unstable, leading to a subsequent reduction in rainfall globally and disproportionately over land where diminished land water storage and runoff were a consequence of the eruption.
As these terrestrial and atmospheric changes are associated with reductions in their storage of water, their initial influence was to delay by about six months the eruption's main effect on sea level, which was a significant and rapid drop arising from a reduction in ocean heat content (OHC). The short timescale of the terrestrial and atmospheric influences relative to the oceans however limited their persistence, and by the beginning of the altimeter era in 1993, a GMSL drop of 5 to 7 mm from the eruption is estimated to have occurred, due largely to cooling of the oceans. While the LE's estimated OHC deficit is difficult to verify directly, given the large uncertainties and errors inherent in global ocean observations, confidence in the simulated response is bolstered by satellite estimates of the Earth's radiative imbalance, which strongly constrain the magnitude of ocean cooling and agree closely with simulated fluxes. Confidence in the ability of the LE to capture fundamental features of the eruption is therefore high.
Legend to Figure 55: Shown are changes in (A) clear-sky albedo over the tropical oceans (30ºN – 30ºS) as an indicator of the eruption's radiative effects and associated global mean sea level (GMSL) anomalies. In (B) contributions from ocean heat content (OHC) atmospheric water vapor (PW) and terrestrial water storage (TWS) estimated from the LE are shown. The large standard deviation across ensemble members (shaded) highlights the obscuring effect of natural climate variability on the eruption's influence in observations.
Discussion: This assessment of the sea level budget during Mt Pinatubo's 1991 eruption and in the several years thereafter has far reaching implications. First, it suggests that our monitoring of sea level via altimetry began in a highly anomalous environment, one in which OHC had been significantly depressed by the eruption while the offsetting influences of the atmosphere and land surface had largely diminished. As the oceans equilibrated from Pinatubo's initial cooling, the sea level experienced an anomalously rapid rise. It is therefore suggested that the GMSL rise estimated from the past decade is likely to be more representative of the background rate due to climate change than that observed during altimetry's initial decade. The eruption of Pinatubo is therefore also reaffirmed as a contributor to the apparently large shift in the rates of rise between the gauge and altimeter eras, consistent with the findings of previous studies.
The budgets simulated by the LE also have implications for the estimation of acceleration. From them, it is estimated that the rate of rise from 1993–2002 is subject to anomalous contribution of about 5 to 7 mm from the recovery to Pinatubo's oceanic cooling. This contribution therefore likely eclipses the background acceleration inferred from the tide gauge record. Given however that no such major eruption has occurred since 1991, a reasonable expectation is also that an accelerated rate of rise may emerge in the near future, particularly as the influences of climate variability and instrument drift reported in previous studies abate.
An estimate of this near-future GMSL acceleration can be made using LE projections of OHC, TWS, and PW in conjunction with independent estimates of future ice sheet losses (Figures 56 and 57). The estimate suggests that, as discussed above, it is unsurprising that acceleration has yet to be detected given the forced response to Pinatubo and the noise of internal climate variability in both OHC and TWS (shaded regions of Figs 2–4), and potential retrieval biases12. Moreover, the result also demonstrates that as anthropogenic influences continue to increase (as a result of both increasing greenhouse gas concentrations and decreasing anthropogenic aerosol emissions), a detectable acceleration of GMSL rise is likely to emerge as it exceeds the noise of background climate variability (shaded) in the coming years. The main contributor to this acceleration is the accelerated increase in OHC, which is offset somewhat by increasing but secondary influences from atmospheric and terrestrial storage, while a key component of the noise obscuring acceleration is the variability of TWS. Moreover, when the effects of the Mt Pinatubo eruption estimated form the LE are removed (blue), acceleration becomes apparent, even in the present day. The magnitude of the acceleration in the mid-21st century is estimated here to be 0.12 mm yr-2, though this value depends strongly on future ice sheet losses, which are highly uncertain1. Its accurate estimation depends both on the accuracy of altimeter retrievals and our ability to distinguish it from internal variability, which can be pronounced in some years but over the long term becomes increasingly negligible, particularly if acceleration is estimated from the full post-1993 record (red line in Figure 57).
With the launch of Jason-3 earlier this year, it is reasonable to ask what new climate insights the instrument may bring. This analysis concludes that if the lifespan of the instrument is comparable to that of its predecessor, Jason-2, the acceleration suggested in earlier studies will likely emerge from the noise of internal climate variability during its lifetime, barring another major volcanic eruption. Moreover, given the unique strengths of sea level as a stable and holistic measure of climate change, the broader altimeter record is likely to stand as one of the benchmark measures of accelerating changes in the climate system.
Legend to Figure 56: Shaded are 1σ (light) and 2σ ranges of internal variability. The mean LE estimate with Pinatubo effects removed is also shown (blue) along with the altimeter record (red).
Legend to Figure 57: Acceleration with Pinatubo effects removed is also shown (blue). The 2σ spread in simulated acceleration estimates is shown for all contributions (light grey) and the contribution due to TWS alone (dark grey).
Difficulties in Making Weather Measurements in the Arctic
• July 21, 2016: A new NASA-led study finds that almost one-fifth of the global warming that has occurred in the past 150 years has been missed by historical records due to quirks in how global temperatures were recorded. The study explains why projections of future climate based solely on historical records estimate lower rates of warming than predictions from climate models. 78)
The study applied the quirks in the historical records to climate model output and then performed the same calculations on both the models and the observations to make the first true apples-to-apples comparison of warming rates. With this modification, the models and observations largely agree on expected near-term global warming. The results were published in the journal Nature Climate Change. Mark Richardson of NASA's Jet Propulsion Laboratory, Pasadena, California, is the lead author. 79)
The Arctic is warming faster than the rest of Earth, but there are fewer historic temperature readings from there than from lower latitudes because it is so inaccessible. A data set with fewer Arctic temperature measurements naturally shows less warming than a climate model that fully represents the Arctic. — Because it isn't possible to add more measurements from the past, the researchers instead set up the climate models to mimic the limited coverage in the historical records.
The new study also accounted for two other issues. First, the historical data mix air and water temperatures, whereas model results refer to air temperatures only. This quirk also skews the historical record toward the cool side, because water warms less than air. The final issue is that there was considerably more Arctic sea ice when temperature records began in the 1860s, and early observers recorded air temperatures over nearby land areas for the sea-ice-covered regions. As the ice melted, later observers switched to water temperatures instead. That also pushed down the reported temperature change.
Scientists have known about these quirks for some time, but this is the first study to calculate their impact. "They're quite small on their own, but they add up in the same direction," Richardson said. "We were surprised that they added up to such a big effect."
These quirks hide around 19 percent of global air-temperature warming since the 1860s. That's enough that calculations generated from historical records alone were cooler than about 90 percent of the results from the climate models that the IPCC (Intergovernmental Panel on Climate Change) uses for its authoritative assessment reports. In the apples-to-apples comparison, the historical temperature calculation was close to the middle of the range of calculations from the IPCC's suite of models.
Any research that compares modeled and observed long-term temperature records could suffer from the same problems, Richardson said. "Researchers should be clear about how they use temperature records, to make sure that comparisons are fair. It had seemed like real-world data hinted that future global warming would be a bit less than models said. This mostly disappears in a fair comparison."
Antarctic Sea-ice Expansion Driven by Tropical Pacific Decadal Climate Variability
• July 4, 2016: The recent trend of increasing Antarctic sea ice extent — seemingly at odds with climate model projections — can largely be explained by a natural climate fluctuation, according to a new study led by NCAR (National Center for Atmospheric Research) of Boulder, CO. The study offers evidence that the negative phase of the IPO (Interdecadal Pacific Oscillation), which is characterized by cooler-than-average sea surface temperatures in the tropical eastern Pacific, has created favorable conditions for additional Antarctic sea ice growth since 2000. 80) The findings, published in the journal Nature Geoscience, may resolve a longstanding mystery: Why is Antarctic sea ice expanding when climate change is causing the world to warm? 81)
The study's authors also suggest that sea ice may begin to shrink as the IPO switches to a positive phase. "The climate we experience during any given decade is some combination of naturally occurring variability and the planet's response to increasing greenhouse gases," said NCAR scientist Gerald Meehl, lead author of the study. "It's never all one or the other, but the combination, that is important to understand."
Study co-authors include Julie Arblaster of NCAR and Monash University in Australia, Cecilia Bitz of the University of Washington, Christine Chung of the Australian Bureau of Meteorology, and NCAR scientist Haiyan Teng. The study was funded by the U.S. Department of Energy and by the National Science Foundation, which sponsors NCAR.
The sea ice surrounding Antarctica has been slowly increasing in area since the satellite record began in 1979. But the rate of increase rose nearly five fold between 2000 and 2014, following the IPO transition to a negative phase in 1999.
The new study finds that when the IPO changes phase, from positive to negative or vice versa, it touches off a chain reaction of climate impacts that may ultimately affect sea ice formation at the bottom of the world.
When the IPO transitions to a negative phase, the sea surface temperatures in the tropical eastern Pacific become somewhat cooler than average when measured over a decade or two. These sea surface temperatures, in turn, change tropical precipitation, which drives large-scale changes to the winds that extend all the way down to Antarctica.
The ultimate impact is a deepening of a low-pressure system off the coast of Antarctica known as the Amundsen Sea Low. Winds generated on the western flank of this system blow sea ice northward, away from Antarctica, helping to enlarge the extent of sea ice coverage.
"Compared to the Arctic, global warming causes only weak Antarctic sea ice loss, which is why the IPO can have such a striking effect in the Antarctic," said Bitz. "There is no comparable natural variability in the Arctic that competes with global warming."
Sifting Through Simulations:
To test if these IPO-related impacts were sufficient to cause the growth in sea ice extent observed between 2000 and 2014, the scientists first examined 262 climate simulations created by different modeling groups from around the world.
When all of those simulations are averaged, the natural variability cancels itself out. For example, simulations with a positive IPO offset those with a negative IPO. What remains is the expected impact of human-caused climate change: a decline in Antarctic sea ice extent.
But for this study, the scientists were not interested in the average. Instead, they wanted to find individual members that correctly characterized the natural variability between 2000-2014, including the negative phase of the IPO. The team discovered 10 simulations that met the criteria, and all of them showed an increase in Antarctic sea ice extent across all seasons.
"When all the models are taken together, the natural variability is averaged out, leaving only the shrinking sea ice caused by global warming," Arblaster said. "But the model simulations that happen to sync up with the observed natural variability capture the expansion of the sea ice area. And we were able to trace these changes to the equatorial eastern Pacific in our model experiments."
Scientists suspect that in 2014, the IPO began to change from negative to positive. That would indicate an upcoming period of warmer eastern Pacific Ocean surface temperatures on average, though year-to-year temperatures may go up or down, depending on El Niño/La Niña conditions. Accordingly, the trend of increasing Antarctic sea ice extent may also change in response.
"As the IPO transitions to positive, the increase of Antarctic sea ice extent should slow and perhaps start to show signs of retreat when averaged over the next 10 years or so," Meehl said.
Climate Change May Shift or Shrink Penguin Habitat in Antarctica
• July 13, 2016: For thousands of years, spells of warm weather along the coast of Antarctica helped penguin populations thrive. Milder weather meant more bare-rock locations for the birds to lay their eggs and nurture their chicks, as well as less stress on the parents and newborns and less sea ice to fight through in the harbors. But over the past few decades, some parts of the southern continent have turned too warm—particularly the water—due to global climate change. According to a new study, that warmth is likely to change where Adélies can raise chicks. 82)
The contribution of climate change to shifts in a species' geographic distribution is a critical and often unresolved ecological question. Climate change in Antarctica is asymmetric, with cooling in parts of the continent and warming along the West Antarctic Peninsula (WAP). The Adélie penguin (Pygoscelis adeliae) is a circumpolar meso-predator exposed to the full range of Antarctic climate and is undergoing dramatic population shifts coincident with climate change. 83)
Using observations of penguin populations and of environmental conditions, as well as computer models of projected environmental changes, the team of researchers projected that nearly a third of Adélie penguin colonies around Antarctica (representing about 20 percent of the total population) could be in decline by 2060. By the end of the 21st century, as much as 60 percent of the colonies could be in trouble. On the other hand, some new refuges on other parts of the coast could open up and offset the losses.
"It is only in recent decades that we know Adélie penguins population declines are associated with warming, which suggests that many regions of Antarctica have warmed too much and that further warming is no longer positive for the species," said Megan Cimino.
The maps of Figures 59 and 60 were built from previous observations (in-person counts and satellite studies) of penguin populations. Red dots mark colonies that have been declining in population—most notably along the Antarctic Peninsula, one of the fastest-warming places on Earth. Blue dots show the location of growing colonies, which often matches where temperatures have been stable or somewhat cooler. Yellow dots denote stable penguin populations.
Warmer temperatures can open up land-based habitat for the penguins, while also keeping waterways ice-free and making it less arduous to search for food. But those warmer temperatures can also make the waters less hospitable (too warm; too little plankton) for the krill and fish that penguins eat. On the other hand, some coastlines could become more hospitable in the future—warming enough to create more habitat, but not enough to disrupt the food supply. The Cape Adare region on Ross Sea is one such area.
Legend to Figure 59: Each colored circle represents a colonies' current population trend. The black dashed line separates West Antarctic Peninsula (WAP) from continental Adélie penguin colonies.
El Niño Conditions in 2015 and Early 2016 Altered Rainfall Patterns Around the World
• July 5, 2016: In the Amazon basin, El Niño reduced rainfall during the wet season, leaving the region drier at the start of the 2016 dry season than any year since 2002. "Severe drought conditions at the start of the dry season have set the stage for extreme fire risk in 2016 across the southern Amazon," said Doug Morton, an Earth scientist at NASA/GSFC (Goddard Space Flight Center) and a co-creator of the fire forecast. The wildfire risk for July to October now exceeds the fire risk in 2005 and 2010—drought years when wildfires burned large swaths of the rainforest. 84)
- The Amazon fire forecast analyzes the relationship between certain climate observations and active fire detections from NASA satellites to predict fire season severity. Developed in 2011 by scientists at the University of California, Irvine (UC Irvine) and NASA, the forecast model is focused particularly on the link between sea surface temperatures and fire activity. Warmer sea surface temperatures in the tropical Pacific (as observed during an El Niño) and Atlantic oceans shift rainfall away from the Amazon region, increasing the risk of fire during dry months.
- The forecast team also tracks changes in water storage during the dry season. The maps of Figure 61 show the accumulated deficit in the rainfall input to surface and underground water storage in 2016 and other recent drought years, as reported by the GPCC (Global Precipitation Climatology Centre). The accumulated deficit is measured from August through May; for example, August 2015 to May 2016 sets the stage for the 2016 dry season. Shades of red depict areas where rainfall has been below normal, while blues were above normal.
- For 2016, El Niño-driven conditions are far drier than in 2005 and 2010—the last years when the region experienced drought. The prediction team has developed a web tool to track the evolution of the fire season in near-real time by Amazon region. Estimated fire emissions from each region are updated daily based on active fire detections—made by the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA's Terra satellite—and data from previous years in the Global Fire Emissions Database. So far, the region has seen more fires through June 2016 than in previous years, another indicator of a potentially tough season.
- "When trees have less moisture to draw upon at the beginning of the dry season, they become more vulnerable to fire and evaporate less water into the atmosphere," said UC-Irvine scientist Jim Randerson, who collaborated with UC-Irvine scientist Yang Chen on building the forecast model. "This puts millions of trees under stress and lowers humidity across the region, allowing fires to grow bigger than they normally would."
- NASA and UC-Irvine scientists have worked in recent years with South American officials and scientists to make them aware of the forecast. Liana Anderson, a from Brazil's National Center for Monitoring and Early Warning of Natural Disasters, said "fire forecasts three to six months before peak fire activity are important to identify areas with higher fire probability for integrated planning."
- The fire forecast team is also working to improve wildfire forecasts in other regions of the world. The scientists recently identified nine regions outside the Amazon where fire season risk could be forecast three- to six months ahead of peak fire activity. Randerson said it may be possible to build seasonal fire forecasts for much of Central America and for many countries in Southeast Asia.
Sea Ice Differences at Earth's Poles
May 2016: Why has the sea ice cover surrounding Antarctica been increasing slightly, in sharp contrast to the drastic loss of sea ice occurring in the Arctic Ocean? A new NASA-led study finds the geology of Antarctica and the Southern Ocean are responsible. 85)
A NASA/NOAA/university team led by Son Nghiem of NASA/JPL (Jet Propulsion Laboratory), Pasadena, California, used satellite radar, sea surface temperature, land form and bathymetry (ocean depth) data to study the physical processes and properties affecting Antarctic sea ice. They found that two persistent geological factors — the topography of Antarctica and the depth of the ocean surrounding it — are influencing winds and ocean currents, respectively, to drive the formation and evolution of Antarctica's sea ice cover and help sustain it. "Our study provides strong evidence that the behavior of Antarctic sea ice is entirely consistent with the geophysical characteristics found in the southern polar region, which differ sharply from those present in the Arctic," said Nghiem.
The Antarctic sea ice cover is dominated by first-year (seasonal) sea ice. Each year, the sea ice reaches its maximum extent around the frozen continent in September and retreats to about 17 percent of that extent in February. Since the late 1970s, its extent has been relatively stable, increasing just slightly; however, regional differences are observed.
Over the years, scientists have floated various hypotheses to explain the behavior of Antarctic sea ice, particularly in light of observed global temperature increases. Are changes in the ozone hole involved? Could fresh meltwater from Antarctic ice shelves be making the ocean surface less salty and more conducive to ice formation, since salt inhibits freezing? Are increases in the strength of Antarctic winds causing the ice to thicken? Something is protecting Antarctic sea ice, but a definitive answer has remained elusive.
To tackle this cryospheric conundrum, Nghiem and his team adopted a novel approach. They analyzed radar data from NASA's QuikSCAT satellite from 1999 to 2009 to trace the paths of Antarctic sea ice movements and map its different types. They focused on the 2008 growth season, a year of exceptional seasonal variability in Antarctic sea ice coverage.
Their analyses revealed that as sea ice forms and builds up early in the sea ice growth season, it gets pushed offshore and northward by winds, forming a protective shield of older, thicker ice that circulates around the continent. The persistent winds, which flow downslope off the continent and are shaped by Antarctica's topography, pile ice up against the massive ice shield, enhancing its thickness. This band of ice, which varies in width from roughly 100 to 1,000 km, encapsulates and protects younger, thinner ice in the ice pack behind it from being reduced by winds and waves.
The team also used QuikSCAT radar data to classify the different types of Antarctic sea ice. Older, thicker sea ice returns a stronger radar signal than younger, thinner ice does. They found the sea ice within the protective shield was older and rougher (due to longer exposure to wind and waves), and thicker (due to more ice growth and snow accumulation). As the sea ice cover expands and ice drifts away from the continent, areas of open water form behind it on the sea surface, creating "ice factories" conducive to rapid sea ice growth.
To address the question of how the Southern Ocean maintains this great sea ice shield, the team combined sea surface temperature data from multiple satellites with a recently available bathymetric chart of the depth of the world's oceans. Sea surface temperature data reveal that at the peak of ice growth season, the boundary of the ice shield remains behind a -1º Celsius temperature line surrounding Antarctica. This temperature line corresponds with the southern Antarctic Circumpolar Current front, a boundary that separates the circulation of cold and warm waters around Antarctica. The team theorized that the location of this front follows the underwater bathymetry.
When they plotted the bathymetric data against the ocean temperatures, the pieces fit together like a jigsaw puzzle. Pronounced seafloor features strongly guide the ocean current and correspond closely with observed regional Antarctic sea ice patterns. For example, the current stays near Bouvet Island, located 1,600 km from the nearest land, where three tectonic plates join to form seafloor ridges. Off the coast of East Antarctica, the -1º Celsius sea surface temperature lines closely bundle together as they cross the Kerguelen Plateau (a submerged microcontinent that broke out of the ancient Gondwana supercontinent), through a deep channel called the Fawn Trough. But those lines spread apart over adjacent deep ocean basins, where seafloor features are not pronounced. Off the West Antarctica coast, the deep, smooth seafloor loses its grip over the current, allowing sea ice extent to decrease and resulting in large year-to-year variations.
The study results are published in the journal Remote Sensing of Environment. 86) Other participating institutions include the Joint Institute for Regional Earth System Science and Engineering at UCLA; the Applied Physics Laboratory at the University of Washington in Seattle; and the U.S. National/Naval Ice Center, NOAA Satellite Operations Facility in Suitland, Maryland. Additional funding was provided by the National Science Foundation.
Methane and Carbon Dioxide on the Rise in the Period 2003-2014
• May 2016: Satellite readings show that atmospheric methane and carbon dioxide are continuing to increase despite global efforts to reduce emissions. Methane concentrations were somewhat constant until 2007, but since then have increased at about 0.3% per year, whereas global carbon dioxide levels continue to rise at about 0.5% per year. The reason for this recent methane increase is not fully understood, but scientists attribute it to several sources such as agriculture and fossil fuels. 87)
The data also show seasonal fluctuations, such as higher concentrations of methane in India and China during August and September. This is because wetlands and rice paddies are a major source of methane and emissions are largest if it is warm and humid. - Other regions such as the Tropics, the USA and parts of Russia experience similar seasonal changes.
Carbon dioxide shows similar seasonal fluctuations, albeit with a maximum concentration earlier in the season at northern latitudes. This is due to the regular uptake and release of carbon dioxide by the growing and decay of terrestrial vegetation: photosynthesis, respiration and decay of organic matter. Overall, carbon dioxide has shown a steady increase over the past decade despite global efforts to reduce emissions.
Currently, plants take up about 25% of the carbon dioxide we are emitting and, without this, atmospheric carbon dioxide levels and related consequences would be much larger," said Michael Buchwitz from the IUP (Institute of Environmental Physics) of the University of Bremen in Germany. "However, we do not know how plants will respond to a changing climate. Our understanding of the ‘land carbon sink' is limited. A goal of the satellite carbon dioxide observations is to close related knowledge gaps, which will lead to improved climate prediction."
The upcoming Sentinel-5P mission(launch scheduled for October 2016) for Europe's Copernicus program is set to continue data collection on methane and other components of atmospheric chemistry by scanning the whole globe every day. "For the future, Sentinel-5P will be very important, in particular because of its very dense, high-resolution observations of atmospheric methane, which have the potential to detect and quantify the emissions of important methane emission hot spots such as oil and gas fields," noted Michael Buchwitz, who also leads the Greenhouse Gases project under ESA's Climate Change Initiative.
The newly released ‘Climate Research Data Package No. 3' covers more than one decade (2003–14) of atmospheric data products used to get information on the sources and sinks of carbon dioxide and methane. 88) The atmospheric data products are available through the GHG-CCI website.89)
GHG-CCI (Green House Gas-Climate Change Initiative): Carbon dioxide (CO2) and methane (CH4) are the two most important anthropogenic greenhouse gases (GHGs). Satellite observations combined with modelling helps to improve our knowledge on CO2 and CH4 sources and sinks as required for better climate prediction. GHG-CCI aims at delivering the high quality satellite retrievals needed for this application.
The Timescales of Global Surface-ocean Connectivity
• April 2016: The billions of single-celled marine organisms known as phytoplankton can drift from one region of the world's oceans to almost any other place on the globe in less than a decade, Princeton University researchers have found.- Unfortunately, the same principle can apply to plastic debris, radioactive particles and virtually any other man-made flotsam and jetsam that litter our seas, the researchers found. Pollution can thus become a problem far from where it originated within just a few years. 90) 91)
The finding that objects can move around the globe in just 10 years suggests that ocean biodiversity may be more resilient to climate change than previously thought, according to a study published this week in the journal Nature Communications. Phytoplankton form the basis of the marine food chain, and their rapid spread could enable them to quickly repopulate areas where warming seas or ocean acidification have decimated them.
"Our study shows that the ocean is quite efficient in moving things around," said Bror Fredrik Jönsson, an associate research scholar in Princeton's Department of Geosciences, who conducted the study with co-author James R. Watson, a former Princeton postdoctoral researcher who is now a researcher at Stockholm University. "This comes as a surprise to a lot of people, and in fact we spent about two years confirming this work to make sure we got it right," Jönsson said.
One of the strengths of the model is its approach of following phytoplankton wherever they go throughout the world rather than focusing on their behavior in one region, Jönsson said. Because most marine organisms are mobile, this particle-tracking approach can yield new insights compared to the approach of studying one area of ocean.
The resulting model works for objects that have no ability to control their movement such as phytoplankton, bacteria and man-made debris. Organisms that can control their movement even a small amount — such as zooplankton, which can control their vertical position in water — are not accounted for in the model. Nor does the model apply to objects such as boats that protrude above the water and can be pushed by surface winds.
The team applied a computer algorithm to calculate the fastest route an object can travel via ocean currents between various points on the globe. Most previous studies looked only at movement of phytoplankton within regions. The resulting database, Jönsson said, is analogous to a mileage chart one would find on a roadmap or atlas showing the distance between two cities, except that Jönsson and Watson are indicating the speed of travel between different points.
The researchers confirmed that the travel times calculated by their model were similar to the time it took real objects accidentally dumped into the ocean to be carried by currents. For instance, 29,000 rubber ducks and other plastic bath toys toppled off a Chinese freighter in 1992 and have since been tracked as a method of understanding ocean currents. A similar utility has stemmed from the "Great Shoe Spill of 1990" when more than 60,000 Nike athletic shoes plunged into the ocean near Alaska and have been riding the currents off the Pacific Northwest ever since.
The researchers' model also matched the amount of time it took radioactive particles to reach the West Coast of the United States from Japan's Fukushima I Nuclear Power Plant, which released large amounts of radioactive materials into the Pacific Ocean following heavy damage from a tsunami in March 2011. The actual travel time of the materials was 3.6 years; the model calculated it would take 3.5 years.
To create the model, Jönsson and Watson obtained surface-current data from a database of modeled global surface currents developed at the MIT (Massachusetts Institute of Technology) and housed at NASA's Jet Propulsion Laboratory in California. Into this virtual world, they released thousands of particles that represented phytoplankton and then ran simulations multiple times, comparing past and present runs for accuracy and making tweaks to improve the model. They eventually tracked more than 50 billion positions of particles, which is just a fraction of the actual number of phytoplankton in the ocean.
Because phytoplankton mainly reproduce asexually — meaning that one organism alone can produce offspring — only one individual needs to reach a new area to colonize it. This fact led the team to look at the shortest time it takes to get around the world rather than the average time. "The rule for our phytoplankton was 'drive at fast as possible,'" Jönsson said.
To cut down the computing resources needed to track the particles, the researchers calculated the fastest way to get from one place to another using a shortcut commonly employed by smartphone apps and in-car navigation systems. The method, called "Dijkstra's algorithm" after the late Dutch computer scientist Edsger Dijkstra who developed it in the 1950s, calculates how to get from A to C if you know the route from A to B and B to C. "Dijkstra's algorithm is a way of optimizing for the shortest path between two positions when you have a network of possible locations, and we used it to find pathways when there was no direct link from one region to another," Watson said.
Although each step in the pathway from one region to another may be unlikely, the fact that a single phytoplankton organism, which lives only a few weeks, can give rise to millions of offspring means that even unlikely paths will have some followers.
Professor of Marine Sciences Per Jonsson at the University of Gothenburg Center for Sea and Society in Sweden said that the analysis offers a new perspective on global connectivity. "This is the first attempt to identify time scales of connectivity and possible dispersal barriers for plankton across all oceans," said Jonsson, who had no role in the research and is not related to study author Bror Jönsson. "The general message is that all parts of the ocean surface are connected on surprisingly short time scales.
"This implies that regional declines in plankton fitness due to climate change may be buffered by relatively rapid immigration coupled with community sorting or evolutionary change," Jonsson continued. "The authors also offer a practical and predictive tool for a range of studies regarding global ocean dispersal, including the spread of contaminants and marine litter."
The paper, "The timescales of global surface-ocean connectivity," was published online in-advance-of-print April 19 in the journal Nature Communications. The work was funded in part by the National Science Foundation, NASA and the Nippon Foundation-University of British Columbia's Nereus Program.
Evidence for Ice-free Summers 6-10 Million Years Ago in the Central Arctic Ocean
• April 2016: An international team of scientists led by the AWI (Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research) in Bremerhaven, Germany have managed to open a new window into the climate history of the Arctic Ocean. Using unique sediment samples from the Lomonosov Ridge, the researchers found that six to ten million years ago the central Arctic was completely ice-free during summer and sea-surface temperature reached values of 4 -9º Celsius. In spring, autumn and winter, however, the ocean was covered by sea ice of variable extent, the scientists explain in the current issue of the journal Nature Communications. These new findings from the Arctic region provide new benchmarks for ground-truthing global climate reconstructions and modelling. 92) 93)
Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014. "The Arctic sea ice is a very critical and sensitive component in the global climate system. It is therefore important to better understand the processes controlling present and past changes in sea ice. In this context, one of our expedition's aims was to recover long sediment cores from the central Arctic, that can be used to reconstruct the history of the ocean's sea ice cover throughout the past 50 million years. Until recently, only a very few cores representing such old sediments were available, and, thus, our knowledge of the Arctic climate and sea ice cover several millions of year ago is still very limited," explained Rüdiger Stein, AWI geologist, expedition leader and lead author of the study.
The AWI researchers discovered an ideal place for recovering the sediment cores on the western slope of the Lomonosov Ridge, a large undersea mountain range in the central Arctic. "This slope must have experienced gigantic recurring landslides in the past, which resulted in the exhumation of more than 500 m thick ancient sediment and rock formations. We were also surprised about the wide-spread occurrence of these slide scars, which extend over a length of more than 300 km, almost from the North Pole to the southern end of the ridge on the Siberian side," said Rüdiger Stein.
Within a two-day coring action, Stein and his team took 18 sediment cores from this narrow area on Lomonosov Ridge on board the Polarstern research vessel. Although the recovered sediment cores were only four to eight meter long, one of them turned out to be precisely one of those climate archives that the scientists had been looking for a long time. "With the help of certain microfossils, so-called dinoflagellates, we were able to unambiguously establish that the lower part of this core consists of approximately six to eight million-year-old sediments, thereby tracing its geological history back to the late Miocene. With the help of so-called ‘climate indicators or proxies', this gave us the unique opportunity to reconstruct the climate conditions in the central Arctic Ocean for a time period for which only very vague and contradictory information was available," said Rüdiger Stein.
Some scientists were of the opinion that the central Arctic Ocean was already covered with dense sea ice all year round six to ten million years ago – roughly to the same extent as today. The new research findings contradict this assumption. "Our data clearly indicate that six to ten million years ago, the North Pole and the entire central Arctic Ocean must in fact have been ice-free in the summer," explained Rüdiger Stein.
There is a general consensus that the polar regions—and in particular the Arctic Ocean and surrounding areas—are at present, and were over historic and geologic time scales, subject to rapid and dramatic environmental changes. Owing to complex feedback processes, collectively known as ‘polar amplification', the Arctic is both a contributor to climate change and a region that will be most affected by global warming. Despite the importance of the Arctic Ocean in the global climate system, this permanently to seasonally ice-covered region (Figure 67) is one of the last major physiographic provinces on Earth, whose climate history and its transition from early Cenozoic Greenhouse to late Cenozoic Icehouse conditions remain still poorly known. Only one drill site recovered from the central Arctic Ocean during the ACEX (Arctic Coring Expedition)—the IODP (Integrated Ocean Drilling Program) Expedition 302 in 2004—gives some insight into the early Cenozoic climate (Ref. 93).
Concerning recent climate change, the most prominent example is the dramatic decrease of the extent and thickness of the Arctic sea-ice cover the last decades, a decrease that seems to be by far more rapid than predicted by climate models. The scientific community recognized this drastic change with major concern as the Arctic sea ice is a critical component in the global climate system, which contributes to changes in the Earth's albedo, primary productivity and deep-water formation, a driving mechanism for global thermohaline circulation. The causes of these recent changes, that is, natural versus anthropogenic forcings, and their relevance within the global climate system, however, are subject of intense scientific and societal debate. Thus, understanding the processes controlling Arctic sea-ice variability is of overall interest and significance. In this context, records of past climate and sea-ice conditions going beyond instrumental records and representing times of different boundary conditions are of major value: such records can be used to assess the sensitivity of the Earth‘s climate system to changes of different forcing parameters, for example, level of CO2, and to test the reliability of climate models by evaluating their simulations for conditions very different from the modern climate. This type of records giving detailed information about past Arctic sea-ice conditions are still very rare, especially due to the lack of precise proxies for sea-ice reconstructions.
Here, the project applies the new sea-ice biomarker approach together with alkenone-based SSTs (Sea Surface Temperatures) to sediment cores most recently recovered during Polarstern Expedition PS87, to reconstruct upper Miocene Arctic Ocean sea-ice and SST conditions. The proxy data are combined with climate model simulations using a coupled atmosphere-ocean general circulation model with focus on seasonal changes in the high northern latitudes. Based on our new proxy records, we demonstrate that only a seasonal sea-ice cover has been predominant in the central Arctic Ocean during (most of) the Late Miocene time interval. Furthermore, our combined data/modelling approach seems to indicate either relatively high atmospheric CO2 concentrations and/or an overly weak sensitivity of the model to simulate the magnitude of warm polar temperatures in the late Miocene. These new findings from the Arctic region provide new benchmarks for ground-truthing global climate reconstructions and modelling.
Legend to Figure 67: (a) Map of modern August SST with locations of ODP Site 907, ODP Site 910 and IODP Expedition 302 (ACEX) Site, as well as Core PS87/106 (August SST data—average of 1955–2012—from World Ocean Atlas;). (b) Map of summer sea-ice concentration—average of 1988–2007—with locations of studied sites (black dots). Maps a and b produced with Ocean Data View software (source: https://odv.awi.de/). (c) Generalized scheme illustrating (1) sea surface conditions and respective (spring/summer) productivities of ice algae and phytoplankton, and (2) sedimentary contents of IP25, terrigenous biomarkers and IRD, phytoplankton-derived biomarkers and PIP25 index for different settings in the modern Arctic Ocean. Owing to ice melting and related nutrient and sediment release, a stable ice-edge situation is characterized by high concentrations of IP25 and phytoplankton biomarkers, but also by high concentrations of terrigenous biomarkers and IRD. Modern situations at the locations of ACEX and PS87/106, ODP Site 910 (and close-by ODP sites 911 and 912) and ODP Site 907 are indicated.
Large submarine slide scars along Lomonosov Ridge. Polarstern Expedition PS87 was scheduled for August–September 2014 to explore the Lomonosov Ridge area (Figure 68) with the objective of collecting seismic data and sediment cores to reconstruct the short- and long-term climate history and the tectonic evolution of the central Arctic Ocean. More than 3,000 km of high-quality MCS (Multi-Channel Seismic) profiles and B10,000 km of high-quality multibeam bathymetry and sub-bottom sediment-echosounding (PARASOUND) profiles were acquired along the ship's track and numerous sediment cores were recovered (Figure 68).
One major finding of the expedition was the discovery of numerous submarine slide scars that occurred on both sides of the crest of Lomonosov Ridge over a distance of ca. 350 km between 81º07' N and 84º 14' N in water depths from B800 to 1,500 m (Figure 69a). Single scars are up to several km wide and long, and their head walls are 100-500 m high. Swath-bathymetry data indicate that different processes probably triggered slope failures, that various processes of sediment evacuation took place, and that failures occurred at various times. Slide scars were earlier described from a restricted area on Lomonosov Ridge near 88ºN18. However, the wide lateral distribution of mass wasting as presented here is a new discovery.
On top of the southern Lomonosov Ridge in areas between the slide scars, the team discovered SE–NW oriented, streamlined landforms over distances of 4100 km at water depths between 800 and 1,000 m (Figure 69a). These features are interpreted to be glacial lineations that formed beneath grounded ice. Similar unidirectional bed forms have also been identified further east on the East Siberian continental margin where they were related to large and coherent ice masses ESCIS (East Siberian Chukchi Ice Sheet). The lineations identified in this study are similar to those on the East Siberian continental margin with respect to their orthogonal orientations to the proposed center of the former ESCIS.
At the present state of knowledge, the most plausible glacial scenario is a larger than originally proposed ESCIS including an ice shelf extending into the Arctic Ocean, which formed an ice rise on the Southern Lomonosov Ridge over areas presently shallower than 1,000 m. The load and erosional behavior of this ice rise that probably occurred during extended Quaternary glaciations, for example, during MIS 6 (Marine Isotope Stage 6), may have caused physical conditions that triggered the landslides on this part of the Lomonosov Ridge. A MIS 6 age of this erosional event is in line with the proposed age of a major glaciation with extended ice sheets/shelves in Eurasia and East Siberia.
Legend to Figure 68: (a) PS87 cruise track (blue line). AB (Amundsen Basin); AR (Alpha Ridge); GR (Gakkel Ridge); LR (Lomonosov Ridge); MB (Makarov Basin); MR (Mendeleev Ridge); NB (Nansen Basin). Orange circles indicate coring stations, the red asterisk indicates the location of the ACEX Site and the green circle indicates the North Pole (Polarstern reached on 26 August 2014 at 10:23 UTC). (b) Track lines of multibeam bathymetric survey. Color bar indicates water depth in meters (m WD). LR-01A, LR-02A and LORI-05B indicate locations of proposed IODP drill sites51. Areas of Figure 69 a,b are indicated.
Legend to Figure 69: (a) Three-dimensional (3D) image of the swath bathymetry of southern Lomonosov Ridge, showing major slide scars and escarpments, streamlined SE–NW oriented glacial lineations formed beneath grounded ice sheets/streams and transects 1 and 2 with locations of sediment cores. (b) PARASOUND profile across Transect 1 with locations of coring stations. (c) Processed multi-channel seismic profile AWI-20140311 across Transect 1, showing prominent reflectors and age assignments based on correlation between regional seismic lines and well data.
Exhumation of Miocene to lower Quaternary sediments. Sediment removal from the steep slopes of the escarpments exposed older, normally more deeply buried deposits at/near the present seafloor, allowing retrieval of older sediments by gravity coring from Polarstern, rather than expensive drilling. The PARASOUND and MCS profiles suggest that these sedimentary sections are composed of Eocene, Oligocene, Miocene, Pliocene and Quaternary strata (Figure 69 b,c). The age control for the stratigraphic units is based on links of seismic lines to drill site data from the Chukchi Shelf, the ACEX drill site on central Lomonosov Ridge and onshore geology from the New Siberian Islands. After evaluation of the multibeam bathymetry and PARASOUND data, the team selected two transects across the steep western slope of the Lomonosov Ridge for an extensive sediment coring program (Figure 69 a, Transect 1 and Transect 2). In total, 16 sediment cores were recovered from water depths between 900 m (top of Lomonosov Ridge) and 1,500 m (bottom of Lomonosov Ridge), Figure 69 a,b.
Whereas most of the sediment cores of Transect 1 are composed of predominantly upper Quaternary (post slide) deposits, some contain prominent unconformities with lower/pre-Quaternary sediments underneath. At these unconformities, a 50-80 m thick overburden has been removed, as demonstrated in compaction experiments (see ‘Sediment load and compaction experiments'). Unfortunately, the microfossil assemblages (that is,palynomorphs and agglutinated benthic foraminifers) do not allow a precise age determination of the sediments underlying the Quaternary near-surface deposits in most of these cores. The predominance of Quaternary sediments in the cores of Transect 1, however, seems to be supported by the biomarker composition determined in selected cores. Close to zero concentrations or the absence of specific biomarkers indicative for phytoplankton and sea-ice algae productivity point to surface-water conditions similar to those of the central Arctic Ocean during late Quaternary times, characterized by a thick perennial sea-ice cover and SSTs (Sea Surface Temperatures) << 0ºC.
The only core providing a clear indication that old sediments are cropping out near the seafloor is Core PS87/106. In this core recovered at the lower slope at Transect 2 (Figure 69 a), a sharp unconformity or hiatus occurs at 370 cmbsf. This unconformity is characterized by a marked change in color, an abrupt increase in WBD (Wet-Bulk Density); related to enhanced sediment consolidation underneath the hiatus), a significant drop in magnetic susceptibility (MS) and a major change in the biomarker composition, and it separates this interval from the overlying young and unconsolidated (upper Quaternary) sediments (Figure 70).
Legend to Figure 70: (a) LSI (Line-Scan Image), (b) WBD, (c) MS, (d) alkenone-based SST, (e) concentrations of alkenones, (f) dinosterol and (g) brassicasterol as proxy for primary productivity, (h) concentrations of terrigenous sterols (sum of campesterol and b-sitosterol), (i) concentrations of sea-ice proxy IP25 and (j) sea-ice index PdinoIP25. Purple and open triangles indicate the presence or absence of alkenones, respectively. Green line marks depth of the hiatus. Below the hiatus, sediments are overconsolidated. Zero or near-zero concentrations of IP25 and phytoplankton biomarkers are indicative for a closed (spring) sea-ice cover (PdinoIP25 is indetermable and set to ‘1'; see Figure 67). PIP25 values are used to identify low (0–20%), common (20–50%), ice-edge (50–70%) and extended (>70%) sea-ice concentrations (see Figure 67). The section below the hiatus represents about one cold (‘glacial')–warm (‘interglacial') cycle. S1 and S2 indicate two scenarios of different sea-ice concentrations (that is, maximum and transitional/stable ice edge, respectively) within this climate cycle. The interval between the two dashed horizontal lines marks period with minimum sea-ice cover. Using mean sedimentation rates of ~3.2 cm ky-1 (as calculated independently from close-by gravity cores and seismic data), the duration of the climate cycle is ~40 ky.
Late Miocene SST and sea-ice records. The biomarker data of Core PS87/106 suggest significantly different late Miocene paleoenvironmental conditions in comparison with those predominant during Quaternary times (Figure 70). In the upper Miocene sediments, elevated concentrations of alkenones and alkenone-derived SST between 4 and 7ºC (or even 6–9ºC in case other calibrations are used indicate relatively warm, open-water and productive paleoenvironmental conditions in the central Arctic Ocean during the summer season. This is also supported by SST values of >>0 C determined in some samples from the ACEX Site.
The team's results reveal for the first time the occurrence of the biomarker sea-ice proxy IP25 in sediments as old as late Miocene. This proxy was developed by Belt et al. and was before our study only found in Quaternary and Pliocene sediments. The presence of IP25 in the PS87/106 sediments is indicative for the presence of (spring) sea ice in the late Miocene central Arctic Ocean (Figure 67). In comparison with IP25 values from the Arctic Ocean surface sediments and sediment trap data, the absolute IP25 concentrations ranging between 0.05 and 0.15 µg gOC-1 (Figure 70) are more than one order of magnitude lower. These differences are caused by an early degradation of biomarkers that already starts in the water column and reaches its maximum in the uppermost cm of the sediments. On the other hand, both IP25 and phytoplankton biomarker concentrations determined in Core PS87/106 are in the same range than those determined in early-mid Holocene Arctic sediments.
Using the ‘PIP25 Index' as a more semi-quantitative proxy of paleo-sea-ice cover (Figure 1), the team's data from Core PS87/106 point to a variable spring sea-ice coverage of ~20–70% in the lower part and ~100% in the upper part of the sequence (Figure 70). The combination of IP25 and SST data indicates that the central Arctic Ocean must have been relatively warm and ice-free during summer throughout the time interval recovered in the sedimentary section of Core PS87/106 and variable sea ice must have existed during spring when daylight conditions allowed sea-ice algae production (Figures 67 and 71). Furthermore, this implies the presence of an extended sea-ice cover during the dark, cold winter season. These new data clearly support that periods with only a seasonal sea-ice coverage must have occurred in the central Arctic Ocean during most of the late Miocene (Figure 71).
Legend to Figure 71: The seasonal sea-ice cycle and related principal processes controlling productivity and carbon flux at location of central Arctic Ocean Core PS87/106 during the late Miocene are shown for two different scenarios. (a) Scenario 2 (‘warmer/transitional situation') =extended period of spring sea-ice algae productivity and increased IP25 and phytoplankton biomarker fluxes. (b) Scenario 1 (‘cold situation') =restricted period of late spring sea-ice algae productivity and very reduced fluxes (almost to zero) of IP25 and spring phytoplankton biomarkers; Figure 67). MIZ (Marginal Ice Zone), that is, ice-edge situation. The dark period, height of the sun and changing thickness of snow and ice over the year, as well as phytoplankton, zooplankton and sea-ice productivity are shown. IP25 values for the different seasons are indicated.
A Global View of Methane
March 2016: For a chemical compound that shows up nearly everywhere on the planet, methane still surprises us. It is one of the most potent greenhouse gases, and yet the reasons for why and where it shows up are often a mystery. What we know for sure is that a lot more methane (CH4) has made its way into the atmosphere since the beginning of the Industrial Revolution. Less understood is why the ebb and flow of this gas has changed in recent decades. 94)
One can find the odorless, transparent gas miles below Earth's surface and miles above it. Methane bubbles up from swamps and rivers, belches from volcanoes, rises from wildfires, and seeps from the guts of cows and termites (where is it made by microbes). Human settlements are awash with the gas. Methane leaks silently from natural gas and oil wells and pipelines, as well as coal mines. It stews in landfills, sewage treatment plants, and rice paddies.
AIRS (Atmospheric Infrared Sounder) aboard NASA's Aqua satellite offers one spaceborne perspective on the methane in Earth's atmosphere. The map of Figure 72 shows global methane concentrations in January 2016 at a pressure of 400 hPa (hectopascal), or roughly 6 km above Earth's surface. Methane concentrations are higher in the northern hemisphere because both natural- and human-caused sources of methane are more abundant there. Since AIRS observed the methane fairly high in the atmosphere, winds may have transported plumes of gas considerable distances from their sources.
Long-term Global Perspective of Atmospheric Methane:
The long-term, global trend for atmospheric methane is clear. The concentration of the gas was relatively steady for hundreds of thousands of years, but then started to increase rapidly around 1750. The reason is simple: increasing human populations since the start of the Industrial Revolution have meant more agriculture, more waste, and more fossil fuel production. Over the same period, emissions from natural sources have stayed about the same. The charts above, based on a combination of historical ice core data and air monitoring instrument data, depict the rate of increase.
Legend to Figure 73: A combination of historical ice core data and air monitoring instruments reveals a consistent trend: global atmospheric methane concentrations have risen sharply in the past 2000 years
When the focus is just on the past five decades — when modern scientific tools have been available to detect atmospheric methane — there have been fluctuations in methane levels that are harder to explain. Figure 74, based on data collected by NOAA (National Oceanic and Atmospheric Administration), shows variations in the rate of increase in the concentration of methane in the atmosphere between 1984 and 2014.
In 1985, the average methane concentration was 1,620 parts per billion (ppb). By 2015, it had increased to 1,800 ppb. — Before the Industrial Revolution, concentrations held steady at about 700 ppb. — But the rate of increase in recent decades has varied. From the 1980s until 1992, methane was rising about 12 ppb per year. Then came roughly a decade of slower growth at 3 ppb per year. Between 2000 and 2007, atmospheric methane concentrations stabilized. Starting in 2007, they began to rise again and have continued to do so since, increasing at a rate of 6 ppb per year.
Methane Matters: 95)
In recent years, the gas has started to turn up in some surprising places. Nighttime satellite images show points of light—some of them gas flares—in rural parts of North Dakota, Texas, and Colorado. Mysterious craters venting methane have appeared in Siberia's Yamal Peninsula. In October 2014, scientists announced they had discovered satellite signals of a methane hotspot over the Four Corners region of the United States. Radar observations have shown bubbles of methane rising from the depths of the Arctic Ocean. And eye-popping videos on the Internet show scientists lighting methane-rich Alaskan lakes on fire.
Since 2007, methane has been on the rise, and no one is quite sure why. Some scientists think tropical wetlands have gotten a bit wetter and are releasing more gas. Others point to the natural gas fracking boom in North America and its sometimes leaky infrastructure. Others wonder if changes in agriculture may be playing a role. "There is no question that methane is doing some very odd and worrying things," said Euan Nisbet, an atmospheric scientist at Royal Holloway, University of London. The big question is why. Scientists wonder if they will have the right monitoring systems in place to answer that question adequately.
The stakes are high. Global temperatures in 2014 and 2015 were warmer than at any other time in the modern temperature record, which dates back to 1880. The most recent decade was the warmest on the record. And carbon emissions are central to that rise.
Methane makes up just 0.00018 percent of the atmosphere, compared to 0.039 percent for carbon dioxide (CO2 is roughly 200 times more abundant) .Yet scientists attribute about one-sixth of recent global warming to methane emissions; what methane lacks in volume it makes up for in potency. Over a 20-year period, one ton of methane has a global warming potential that is 84 to 87 times greater than carbon dioxide. Over a century, that warming potential is 28 to 36 times greater. The difference occurs because methane is mostly scrubbed out of the air by chemical reactions within about ten years, while carbon dioxide persists in the atmosphere for much longer than a century.
"That means the climate effects of methane are front-loaded," explained Drew Shindell, a climate scientist at Duke University. "Part of the reason there is so much interest in methane right now is because reducing those emissions could slow warming over the next few decades. This does not let us off the hook for reducing carbon dioxide, but the benefits of carbon dioxide reductions will come much later."
Decade of Rrising Seas Slowed by Land Soaking up Extra Water
• Feb. 12, 2016: New measurements from the GRACE (Gravity Recovery And Climate Experiment) satellite, an international cooperative US-German dual-minisatellite SST (Satellite-to-Satellite Tracking) geodetic mission, have allowed researchers to identify and quantify, for the first time, how climate-driven increases of liquid water storage on land have affected the rate of sea level rise.
A new study by scientists at NASA/JPL (Jet Propulsion Laboratory) in Pasadena, California, and the University of California, Irvine, shows that while ice sheets and glaciers continue to melt, changes in weather and climate over the past decade have caused Earth's continents to soak up and store an extra 3.2 trillion tons of water in soils, lakes and underground aquifers, temporarily slowing the rate of sea level rise by about 20%.
The water gains over land were spread globally, but taken together they equal the volume of Lake Huron, the world's seventh largest lake. The study is published in the Feb. 12 issue of the journal Science. 96) 97) 98)
Each year, a large amount of water evaporates from the ocean, falls over land as rain or snow, and returns to the ocean through runoff and river flows. This is known as the global hydrologic, or water, cycle. Scientists have long known small changes in the hydrologic cycle — by persistent regional changes in soil moisture or lake levels, for instance — could change the rate of sea level rise from what we would expect based on ice sheet and glacier melt rates. However, they did not know how large the land storage effect would be because there were no instruments that could accurately measure global changes in liquid water on land.
The study team used gravity measurements made between 2002 and 2014 by the GRACE (Gravity Recovery And Climate Experiment) mission to quantify variations in groundwater storage. Combining those data with estimates of mass loss by glaciers revealed groundwater's impact on sea-level change. Net groundwater storage has been increasing, and the greatest regional changes, both positive and negative, are associated with climate-driven variability in precipitation. Thus, groundwater storage has slowed the rate of recent sea-level rise by roughly 15%.
"These [gravity field] changes are often caused by the movement of water – and the measurements are actually quite precise," said John Reager of NASA/JPL." An important piece of this study was making sure that we could reduce the uncertainty in the measurement enough to be able to draw these conclusions. This is the first paper to really reduce the uncertainty enough that we could make a statement about what's happening with glaciers and hydrology together, and we needed a lot of expertise to do that – this project had contributions from experts in hydrology, glaciology, geodesy and atmospheric science."
Over the last two decades, sea level has risen at around 3.2 mm per year, roughly double the average rate for the past century, as oceans warm and glaciers and ice sheets melt. From 2003 to 2011 sea-level rise slowed to around 2.4 mm per year, despite increased melting of glaciers and ice sheets. Many see land water storage – in snow, surface water, soil moisture and groundwater, but not glaciers – as one of the most important yet most uncertain contributions to sea-level trends. The latest IPCC (Intergovernmental Panel on Climate Change) report did not include climate-driven changes in land water storage, through variations in rainfall, evaporation and runoff, because of the challenge of measurement.
The study team used estimates of glacier loss and groundwater depletion to separate the GRACE measurements of global changes in surface mass into components for glaciers, direct human-driven land water storage and climate-driven water storage.
Humans can alter land water storage by extracting groundwater, irrigation, using reservoirs, draining wetland and destroying forest. Such activities are estimated to have caused 0.38 mm of sea-level rise per year from 1993 to 2010, around 15–25% of the sea-level rise observed from the addition of water to the oceans.
Legend to Figure 76: Glaciers and ice sheets are excluded. Shown are the global map (gigatons per year per 1/2-degree grid), zonal total trends, full time series (mm/year SLE), and best-fit linear regression with climatology removed (mm/year SLE). The strongest gains and losses are associated with climate-driven variability in precipitation. Note: SLE (Sea Level Equivalent), TWS (Terrestrial Water Storage).
Every year, land temporarily stores then releases a net 6000 ± 1400 Gt (gigtons) of mass through the seasonal cycling of water, which is equivalent to an oscillation in sea level of 17 ± 4 mm. Thus, natural changes in interannual to decadal cycling and storage of water from oceans to land and back can have a large effect on the rate of SLR (Sea Level Rise) on decadal intervals. From 2003 to 2011, SLR slowed to a rate of ~2.4 mm/year during a period of increased mass loss from glaciers and ice sheets. Climate-driven changes in land water storage have been suggested to have contributed to this slowdown, but this assertion has not been verified with direct observations.
Until recently, little data have existed to constrain land water storage contributions to global mean SLR. As a result, this term has either been excluded from SLR budgets or has been approximated by using ad hoc accounting that includes modeling or scaling of a variety of ground-based observations. Human-induced changes in land water storage (hereafter referred to as "human-driven land water storage") include the direct effects of groundwater extraction, irrigation, impoundment in reservoirs, wetland drainage, and deforestation. These activities may play a major role in modulating rates of sea level change, and several studies of large aquifers suggest that trends in regional and global land water storage are now strongly influenced by the effects of groundwater withdrawal. Currently, human activity (including groundwater depletion and reservoir impoundment) is estimated to have directly resulted in a net 0.38 ± 0.12mm/year SLE (Sea Level Equivalent) between 1993 and 2010 or 15 to 25% of observed barystatic SLR, but estimates are acknowledged to have large uncertainties.
Contribution (mm year-1 SLE)
Konikow et al. (2011) 100)
Scaling of in situ measurements
2000 to 2008
0.41 ± 0.10
Wada et al. (2012) 99)
0.57 ± 0.09
Döll et al. (2014) 101)
2000 to 2009
0.31 ± 0.0
IPCC AR5 (2013) 102)
1993 to 2010
0.38 ± 0.12
Richey et al. (2015) 103)
GRACE net subsurface storage
2003 to 2014
0.24 ± 0.02
NASA, NOAA Analyses Reveal Record Warm Temperatures in 2015
• January 20, 2016: Earth's 2015 surface temperatures were the warmest since modern record keeping began in 1880, according to independent analyses by NASA and NOAA (National Oceanic and Atmospheric Administration). Globally-averaged temperatures in 2015 shattered the previous mark set in 2014 by 0.13º Celsius. Only once before, in 1998, has the new record been greater than the old record by this much. 105) 106)
The 2015 temperatures continue a long-term warming trend, according to analyses by scientists at NASA's GISS (Goddard Institute for Space Studies) in New York (GISTEMP). NOAA scientists agreed with the finding that 2015 was the warmest year on record based on separate, independent analyses of the data. Because weather station locations and measurements change over time, there is some uncertainty in the individual values in the GISTEMP index. Taking this into account, NASA analysis estimates 2015 was the warmest year with 94% certainty.
"Climate change is the challenge of our generation, and NASA's vital work on this important issue affects every person on Earth," said NASA Administrator Charles Bolden. "Today's announcement not only underscores how critical NASA's Earth observation program is, it is a key data point that should make policy makers stand up and take notice - now is the time to act on climate."
The planet's average surface temperature has risen about 1.0 degree Celsius since the late-19th century, a change largely driven by increased carbon dioxide and other human-made emissions into the atmosphere. Most of the warming occurred in the past 35 years, with 15 of the 16 warmest years on record occurring since 2001. Last year was the first time the global average temperatures were 1º Celsius or more above the 1880-1899 average.
Phenomena such as El Niño or La Niña, which warm or cool the tropical Pacific Ocean, can contribute to short-term variations in global average temperature. A warming El Niño was in effect for most of 2015. "2015 was remarkable even in the context of the ongoing El Niño," said GISS Director Gavin Schmidt. "Last year's temperatures had an assist from El Niño, but it is the cumulative effect of the long-term trend that has resulted in the record warming that we are seeing."
Weather dynamics often affect regional temperatures, so not every region on Earth experienced record average temperatures last year. For example, NASA and NOAA found that the 2015 annual mean temperature for the contiguous 48 United States was the second warmest on record.
NASA's analyses incorporate surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions if left unaccounted for. The result is an estimate of the global average temperature difference from a baseline period of 1951 to 1980. - NOAA scientists used much of the same raw temperature data, but a different baseline period, and different methods to analyze Earth's polar regions and global temperatures.
GISS is a NASA laboratory managed by the Earth Sciences Division of the agency's Goddard Space Flight Center in Greenbelt, Maryland. The laboratory is affiliated with Columbia University's Earth Institute and School of Engineering and Applied Science in New York.
NASA monitors Earth's vital signs from land, air and space with a fleet of satellites, as well as airborne and ground-based observation campaigns. The agency develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. NASA shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).