The Arctic is changing with a rapidity that has amazed scientists. The Greenland ice sheet is shrinking, sending over 48 cubic miles a year of ice streaming into the oceans, while Arctic sea ice cover continues to track below average. These changes will have significant effects regionally and globally. Scientists from Columbia University's Lamont-Doherty Earth Observatory are flying over the region on a NASA-led mission called Operation IceBridge to understand what is happening on and below the ice.
Location: Greenland Ice Sheet
Team: Jim Cochran, Tim Creyts, Indrani Das
Purpose: Glacier and Climate Research
Start Date: March 30, 2010
Scientists have detected what they say are the sediments of a huge ancient lake bed sealed more than a mile under the ice of northwest Greenland—the first-ever discovery of such a sub-glacial feature anywhere in the world. Apparently formed at a time when the area was ice-free but now completely frozen in, the lake bed may be hundreds of thousands or millions of years old, and contain unique fossil and chemical traces of past climates and life. Scientists consider such data vital to understanding what the Greenland ice sheet may do in coming years as climate warms, and thus the site makes a tantalizing target for drilling. A paper describing the discovery is in press at the journal Earth and Planetary Science Letters.
“This could be an important repository of information, in a landscape that right now is totally concealed and inaccessible,” said Guy Paxman, a postdoctoral researcher at Columbia University’s Lamont-Doherty Earth Observatory and lead author of the report. “We’re working to try and understand how the Greenland ice sheet has behaved in the past. It’s important if we want to understand how it will behave in future decades.” The ice sheet, which has been melting at an accelerating pace in recent years, contains enough water to raise global sea levels by about 24 feet.
The researchers mapped out the lake bed by analyzing data from airborne geophysical instruments that can read signals that penetrate the ice and provide images of the geologic structures below. Most of the data came from aircraft flying at low altitude over the ice sheet as part of NASA’s Operation IceBridge.
The team says the basin once hosted a lake covering about 7,100 square kilometers (2,700 square miles), about the size of the U.S. states of Delaware and Rhode Island combined. Sediments in the basin, shaped vaguely like a meat cleaver, appear to range as much as 1.2 kilometers (three quarters of a mile) thick. The geophysical images show a network of at least 18 apparent onetime stream beds carved into the adjoining bedrock in a sloping escarpment to the north that must have fed the lake. The images also show at least one apparent outlet stream to the south. The researchers calculate that the water depth in the onetime lake ranged from about 50 meters to 250 meters (a maximum of about 800 feet).
In recent years, scientists have found existing subglacial lakes in both Greenland and Antarctica, containing liquid water sandwiched in the ice, or between bedrock and ice. This is the first time anyone has spotted a fossil lake bed, apparently formed when there was no ice, and then later covered over and frozen in place. There is no evidence that the Greenland basin contains liquid water today.
Paxman says there is no way to tell how old the lake bed is. Researchers say it is likely that ice has periodically advanced and retreated over much of Greenland for the last 10 million years, and maybe going back as far as 30 million years. A 2016 study led by Lamont-Doherty geochemist Joerg Schaefer has suggested that most of the Greenland ice may have melted for one or more extended periods some time in the last million years or so, but the details of that are sketchy. This particular area could have been repeatedly covered and uncovered, Paxman said, leaving a wide range of possibilities for the lake’s history. In any case, Paxman says, the substantial depth of the sediments in the basin suggest that they must have built up during ice-free times over hundreds of thousands or millions of years.
“If we could get at those sediments, they could tell us when the ice was present or absent,” he said.
The researchers assembled a detailed picture of the lake basin and its surroundings by analyzing radar, gravity and magnetic data gathered by NASA. Ice-penetrating radar provided a basic topographic map of the earth’ s surface underlying the ice. This revealed the outlines of the smooth, low-lying basin, nestled among higher-elevation rocks. Gravity measurements showed that the material in the basin is less dense than the surrounding hard, metamorphic rocks—evidence that it is composed of sediments washed in from the sides. Measurements of magnetism (sediments are less magnetic than solid rock) helped the team map the depths of the sediments.
The researchers say the basin may have formed along a now long-dormant fault line, when the bedrock stretched out and formed a low spot. Alternatively, but less likely, previous glaciations may have carved out the depression, leaving it to fill with water when the ice receded.
What the sediments might contain is a mystery. Material washed out from the edges of the ice sheet have been found to contain the remains of pollen and other materials, suggesting that Greenland may have undergone warm periods during the last million years, allowing plants and maybe even forests to take hold. But the evidence is not conclusive, in part because it is hard to date such loose materials. The newly discovered lake bed, in contrast, could provide an intact archive of fossils and chemical signals dating to a so-far unknown distant past.
The basin “may therefore be an important site for future sub-ice drilling and the recovery of sediment records that may yield valuable insights into the glacial, climatological and environmental history” of the region, the researchers write. With the top of the sediments lying 1.8 kilometers below the current ice surface (1.1 miles), such drilling would be daunting, but not impossible. In the 1990s, researchers penetrated almost 2 miles into the summit of the Greenland ice sheet and recovered several feet of bedrock—at the time, the deepest ice core ever drilled. The feat, which took five years, has not since been repeated in Greenland, but a new project aimed at reaching shallower bedrock in another part of northwest Greenland is being planned for the next few years.
The study was coauthored Jacqueline Austermann and Kirsty Tinto, both also based at Lamont-Doherty Earth Observatory. The research was supported by the U.S. National Science Foundation.
Scientists know that the brownish-grey algae that darken the Greenland ice sheet in summer cause the ice to melt faster, but only recently have they measured these blooms in the field, and only at few sites. To measure algal blooms across large regions and understand their effects on melting over time, they are now turning to space.
“Scientists go into the field and sample one or two spots where these blooms occur, but we don’t really know how they change over time or over a large region,” said Shujie Wang, lead author of a recent study showing that satellites can be used to track the growth of ice algae over wide areas.
To measure algae growth, Wang and her colleagues borrowed long-standing methodology used by other scientists to measure algae in the oceans, using satellite observations of water color. Marine algae differ from those on ice, but both kinds contain chlorophyll-a, which has a distinct reflected near-infrared radiation signature that satellite sensors can detect.
Mapping glacier algae over space and time can give researchers insights into how algae affect the reflectivity, or albedo, of the ice surface, said Wang, who conducted the research as a postdoctoral scholar at Columbia University’s Lamont-Doherty Earth Observatory. She is now an assistant professor of geography at Penn State University.
“Albedo is crucial for understanding how ice melts and what will happen in the future to the contribution of Greenland to sea level rise,” said Lamont-Doherty research professor Marco Tedesco, who supervised Wang’s work. “Little is known of the effects of algae on this, and the work by Shujie is pioneering in this regard.”
Light-colored snow and ice have a high albedo, meaning that they reflect most incoming solar radiation back to the atmosphere. But when algae accumulate, they darken the surface; this causes it to absorb more radiation, warming the ice and accelerating surface melt.
The researchers used data from the Medium Resolution Imaging Spectrometer (MERIS) on the European Space Agency’s Envisat satellite to quantify algal blooms in southwestern Greenland from 2004 to 2011. They compared the data to measurements taken in the field and by NASA’s Moderate Resolution Imaging Spectrometer (MODIS), which measures surface albedo.
They found that chlorophyll-a signatures captured by MERIS matched field data, confirming that researchers can use ocean-color satellite data to measure algal growth and see how it changes over the summer. The same held true for the albedo changes measured by MODIS.
“We came up with a rough estimate that if algae growth doubles, then albedo decreases between 2 percent to 4 percent,” said Wang. “This biological component has never before been incorporated into climate modeling.”
The researchers also found that years with fewer cloudy days, and therefore more solar radiation, saw more algae development. “Algae need solar radiation to create energy through photosynthesis, so shortwave radiation may be an important factor controlling how much algae will grow or how they’re spatially distributed,” Wang said.
The interplay among climate, algae and ice creates a cycle that can accelerate the melting process. As Greenland warms, higher temperatures are directly causing more ice to melt. But the warming also appears to be changing atmospheric circulation patterns, and recently there has been a trend toward more sunny days. More sunny days means the ice will absorb more solar radiation and melt faster. The solar radiation also promotes algae growth, further accelerating melt.
In addition to improving regional climate models, the research has implications for the exploration of other planets. “Algae and bacteria are the only life on the ice sheet, and it is fascinating to imagine that the areas where they thrive are among the closest thing we can imagine to extraterrestrial life,” said Tedesco, who also holds a position at the NASA Goddard Institute for Space Studies.
The next step is to quantify how much algae development increases the production of melt water. Wang plans to address that question in subsequent research.
Also participating in the research were Patrick Alexander of Lamont-Doherty and Goddard Institute for Space Studies; Min Xu of the University of South Florida; and Xavier Fettweis of the University of Liege, Belgium. The research was supported by the U.S. National Science Foundation, NASA and the Heising-Simons Foundation.
Adapted from a press release by Penn State University.
If human societies don’t sharply curb emissions of greenhouse gases, Greenland’s rate of ice loss this century is likely to greatly outpace that of any century since shortly after the end of the last ice age, a new study concludes.
The findings place the ice sheet’s modern decline in a solid historical context for probably the first time, highlighting just how extreme projected losses for the 21st century could be, researchers say. The research was published this week in the journal Nature.
Scientists used new, detailed reconstructions of ancient climate to drive a model of the past, present and future of the Greenland ice, and validated the model against real-world measurements of the ice sheet’s contemporary and ancient size.
“Basically, we’ve altered our planet so much that the rates of ice sheet melt this century are on pace to be greater than anything we’ve seen under natural variability [over] the past 12,000 years,” said study leader Jason Briner, a geologist at the University at Buffalo.
The researchers say that under a best-case scenario, with society greatly reducing emissions, melting in Greenland in the 21st century will be just slightly higher than that of any other century of the past 12 millennia. But under a high-emissions scenario—the one the Greenland Ice Sheet is now following—the rate of mass loss could be about four times higher.
The study brought together climate modelers, ice core scientists, remote sensing experts and paleoclimate researchers at eight institutions including Columbia University’s Lamont-Doherty Earth Observatory. The team used a state-of-the-art ice sheet model to simulate changes to the southwestern sector of the ice sheet, starting from some 12,000 years ago and extending forward 80 years to 2100. They tested the model’s accuracy by comparing results of the model’s simulations to historical evidence. The modeled results matched up well with data tied to actual measurements of the ice sheet made by satellites and aerial surveys in recent decades, and with field work identifying the ice sheet’s ancient boundaries.
Lamont-Doherty geochemists Nicolás Young and Joerg Schaefer helped build a detailed geologic history of how the margin of the ice sheet moved through time by measuring isotopes of beryllium in boulders left by retreating ice at various times. “Amazingly, the model reproduced the geologic reconstruction really well,” said Young. “This gave us confidence that the ice sheet model was performing well and giving us meaningful results.” Though the project focused on southwestern Greenland, research shows that changes in the rates of ice loss there tend to correspond tightly with changes across the entire ice sheet.
Researchers at the University of California, Irvine and NASA’s Jet Propulsion Laboratory led the modeling. They leveraged the work of colleagues at the University of Washington, who used data from ice cores to create maps of temperatures and precipitation in the study region that were used to drive the ice sheet model simulations up to the year 1850. Previously published climate data was used to drive the simulations after that date. Lamont-Doherty and the University at Buffalo partnered on field work that helped validate the model by identifying the ice sheet’s previous boundaries.
“It is no secret that the Greenland Ice Sheet is in rough shape and is losing ice at an increasing rate,” Young said. But, he said, “I think this is the first time that [its] current health has been robustly placed into a long-term context.”
Despite the sobering results, one vital takeaway is that it is still possible for people around the world to make an important difference by cutting emissions. “Our findings are yet another wake-up call, especially for countries like the U.S.,” said Briner.
The research was largely funded by the U.S. National Science Foundation. The scientists also received support from the Natural Sciences and Engineering Research Council of Canada, Fonds de recherche du Québec, and NASA.
Adapted from a press release by the University at Buffalo.
At the turn of the 21st century, unbeknownst to the world, the Greenland ice sheet likely entered a state of sustained mass loss that will persist for the foreseeable future, according to a new study. Though the finding has raised concern over the future of the ice sheet, scientists emphasize that reducing emissions remains critical.
The study, which looked at 40 years of satellite data, was released on August 13 in Communications Earth & Environment. Second in size only to the Antarctic ice sheets, the Greenland ice sheet covers nearly 80 percent of the vast island. It contains the equivalent of about 24 feet of global mean sea level rise and, due to its accelerated retreat, is considered the largest single contributor to rising sea levels worldwide.
While the ice sheet’s decline has been well-documented over the past two decades, this latest study, led by Michalea King of the Byrd Polar and Climate Research Center, found that widespread glacier retreat helped push the ice sheet from a balanced to an imbalanced state. This work suggests that even if the oceans and atmosphere were to stop warming today, the ice sheet will continue to lose more ice than it will gain.
In the decades leading up to the turn of the century, the ice sheet was in a state of relative equilibrium. The ice lost in a given year would be replenished by wintertime snowfall, and the sheet maintained a near-constant mass. But beginning around the year 2000, ice discharged through outlet glaciers—channels that flow outward to the sea—started to outpace annual snowfall that, in a balanced year, would replenish lost ice. The authors sifted through 40 years of satellite data, tracking outlet glacier velocity, thickness, and calving front position over time to determine the rate of ice loss. The shift they found represents a tipping point that is unlikely to be reversible in the near future. King told GlacierHub, “It’s like a gear change… we’ve accelerated the drainage at the edge of the ice sheet, and now… we expect mass loss to be the new norm for the ice sheet in the near future.”
Ian Howat, director of the Byrd Polar and Climate Research Center and co-author of the paper, explained to GlacierHub that the dynamics of ice loss through outlet glaciers can be likened to the functioning of a dam. “Those glaciers act just like a spillway on a dam,” he said. “The more you open the spillway… the faster the reservoir gets drawn down.” The study suggests that longer-term thinning throughout the 20th century—likely due to warming oceans—led up to a mass retreat event in the early 2000s. The result was a “step-increase” in the rate of discharge through outlet glaciers; before 2000, 420 gigatons of ice were discharged annually. In the years following, the rate increased to 480 gigatons of ice discharged annually. A gigaton is equal to one billion metric tons, roughly the mass of all land mammals (excluding humans) on Earth. “When all of these glaciers retreated at once, it was enough to significantly increase the rate at which ice flows into the ocean. It’s like the spillway on the dam was opened up,” Howat said.
According to King, the significance of this new rate of discharge is that “consistently, more ice is being lost through the flow of these glaciers than is being gained by snow accumulation.” Returning to a balanced state would require an extra 60 gigatons per year of snowfall or reduced melting. Yet under essentially all climate change scenarios, the opposite is expected.
The findings of this study—along with others that document the decline of the Greenland ice sheet—spell worrying news for sea level rise trajectories. Marco Tedesco, research professor of marine geology and geophysics at the Lamont-Doherty Earth Observatory, explained to GlacierHub that the Greenland ice sheet has been, and will increasingly be, a major contributor to rising sea levels. The two primary causes of sea level rise are thermal expansion—ocean water expands as it warms—and the melting of land-based ice. With sea level rise projected to submerge land home to 150 million people permanently below the high tide line (and that estimate assumes stability of the Antarctic ice sheet), Greenland finds itself in the spotlight. “In terms of direct contribution,” Tedesco said, “Greenland is actually the largest contributor now, with about 20 to 25 percent of sea level rise due to Greenland.” Moreover, the percentage of contribution could increase to 30 or 40 percent by the end of the century, according to Tedesco.
The ice loss shown above has resulted in about 0.8 millimeters per year of sea level rise. Source: NASA
Another study on the Greenland ice sheet, coauthored by Tedesco, made international headlines recently, concluding that 2019 was a year of record ice loss. According to scientists, the ice lost in 2019 was double the yearly average since 2003. Ian Joughin, a glaciologist at the University of Washington’s Polar Science Center, connected the dots between these two major studies. “Nobody really, 20 years ago, was expecting glaciers to speed up as rapidly as what we’ve seen,” he told GlacierHub. In terms of annual loss of ice, “people think of it as melting, but it’s basically the balance between how much snow falls each year, and how much icebergs calve off and how much melting actually occurs on the ice sheet itself.” Ultimately, neither melting nor ice discharge alone can explain the changing ice sheet. They are, rather, two processes in a complex dynamic, which glaciologists are racing to understand using a combination of field work, remote sensing, and modeling.
Rapid international action is needed to limit global warming to 1.5˚C, which would allow more time for adaptation to rising sea levels. Addressing recent headlines declaring that the ice sheet has reached the point of no return, a statement that has since been discussed within the scientific community, Howat said, “I think it’s very important to emphasize that this loss of the ice sheet is not irreversible. We’ve witnessed a step-change that is unlikely to be reversible in the near future, but we still have a long way to go and we still have a lot of say in how quickly the ice sheet will continue to retreat.”
An international team of polar researchers says that the Greenland ice sheet experienced record loss in 2019. The reduction of 532 billion tons in mass dramatically broke the previous record year of 2012, when 464 billion tons of ice went into the ocean.
Preliminary analyses had already suggested that 2019 would be Greenland’s worst recorded year. The team confirmed it by evaluating satellite observations and data from computer models.The findings were reported this week in the journal Communications Earth & Environment.
The Greenland ice sheet is a major contributor to global mean sea level rise. It was responsible for about 0.76 millimeters per year, out of a total of about 3.5 millimeters per year from 2005 to 2017. The five biggest years of ice loss in Greenland have all occurred in the past decade. As a result of last year’s losses, global mean sea level rose 1.5 millimeters.
Mass balance of the ice sheet results from the difference between increase due to snowfall and loss due to a combination of melting and iceberg discharges along the edges of the sheet. In 2019, weather conditions heavily favored loss. “By comparing satellite data with regional climate models, we were able to see exactly which process was involved, how much it contributed and which general weather patterns were decisive,” said study coauthor Marco Tedesco, a Lamont-Doherty polar scientist. Among other things, “snowfall was lower than the long-term average; that contributed to the record,” he said.
Using simulations with a regional climate model, the authors attributed the anomalously low melt in 2017–2018 to cold summers in western Greenland and high snowfall in the east.
To determine the 2019 ice loss, researchers from Germany’s Alfred Wegener Institute, and other institutions, including Columbia University’s Lamont-Doherty Earth Observatory, evaluated satellite data from NASA’s GRACE mission and its successor, GRACE Follow-On. The satellites provide measurements from which highly accurate maps of the earth’s gravity can be calculated for each month. The redistribution of masses changes the gravitational attraction in time and space. In Greenland, as ice is lost to the ocean, this redistribution of mass reduces its gravity. The researchers compared the satellite data with simulations of regional climate models that represent snowfall and melting of the ice sheet.
“After two years of a breathing pause, mass losses rose sharply again in 2019 and exceeded all annual losses since 1948, probably since more than 100 years,” said Ingo Sasgen, a glaciologist at the Alfred Wegener Institute and lead author of the study. “More and more often we have stable high pressure systems over the ice sheet, which favor the influx of warmer air from the mid-latitudes, one of the conditions promoting melt. We saw a similar pattern in the previous record year 2012.”
The NASA missions have proven crucial for continuous observation of Greenland. The GRACE mission, which ended in summer 2017, provided observations on ice loss in polar regions over a period of 15 years. After a gap of about a year, monitoring was picked up in summer 2018 by GRACE Follow-On.
Among the phenomena contributing to the increased ice loss, Arctic summer temperatures are increasing about one and a half times faster than the global average.
For years, geologists have debated how and when a network of canyons under the Greenland ice sheet formed, especially one that is so deep and long it’s been called Greenland’s Grand Canyon. Its shape suggests it was carved by running water followed by glaciation, but until now, the genesis of this canyon, and similar features in northern Greenland, have remained unknown.
In a new study in the journal Geology, scientists at the University of Massachusetts Amherst and the University of Copenhagen have proposed a new mechanism for how the mega-canyon formed: from a series of catastrophic outburst floods that suddenly and repeatedly drained lakes of melting ice-sheet water over time. Based on ice-sheet model simulations of the early ice sheet’s history, they show that climate and bedrock topography have exerted strong controls on the ice sheet since its beginning.
First author Benjamin Keisling, now a postdoctoral fellow at Columbia University’s Lamont-Doherty Earth Observatory, did the work as a graduate student with senior author and advisor Rob DeConto at UMass.
Keisling says that before now, repeated outburst floods appeared to be the mechanism by which the Columbia River and other North America canyon networks formed. But they had not been considered as having played a role in forming the tortured landscape under the Greenland ice sheet.
“If the floods we propose occurred, they could have influenced ocean circulation, causing abrupt climate changes with regional and perhaps global significance,” said Keisling. “The mega-canyon beneath northern Greenland also influences how ice and water flow in the subglacial environment today, which affects present-day ice-sheet stability.”
Keisling says that in most Greenland studies, researchers use the modern ice sheet as a starting point for understanding how it has changed over time. But Keisling and his co-authors took a different approach, investigating what Greenland looked like before widespread glaciation. “We wanted to better understand the dynamics of “glacial inception – how, where and why the ice sheet first grew on an ice-free island,” he said.
The team also wanted to gain a better understanding of how the ice sheet grew back after melting. “We know from prior work this has happened multiple times in the past and could again in the future, given enough global warming,” said Keisling.
They used coupled ice-sheet and climate models to simulate the ice sheet’s evolution over many glacial-interglacial cycles in the last few million years. They found that following long periods with stable temperatures, an exceptionally warm period could cause the ice sheet to rapidly retreat. This led to large, ice-dammed lakes forming in areas where the bedrock was still depressed from the old ice sheet’s weight.
Their simulations show the ice dams eventually giving way as large outburst floods. “Over time,” said Keisling, “it appears that the filling and draining of these lakes as the ice repeatedly retreated and advanced carved Greenland’s mega-canyons.” Similar floods have been documented at the edge of other retreating ice sheets, he said.
Comparing Greenland with modern outburst floods, the researchers estimate that as many as hundreds of floods carved its giant canyon. Results suggest testable hypotheses for future research that could settle the long-standing debate about whether the ice sheet’s stability has changed over time, they say.
“Knowing the history of Greenland’s bedrock provides context for understanding the ice sheet’s long-term behavior,” Keisling said. “This helps paint a picture of what happened during past warm periods when the melting ice sheet caused global sea levels to rise, a phenomenon we are also seeing today.”
The work was supported by NASA, the U.S. National Science Foundation, a GROW Fellowship, and the Danish National Research Foundation.
Adapted from a press release by the University of Massachusetts Amherst.
Last year was one of the worst years on record for the Greenland ice sheet, which shrunk by hundreds of billions of tons. According to a study published today in The Cryosphere, that mind-boggling ice loss wasn’t caused by warm temperatures alone; the new study identifies exceptional atmospheric circulation patterns that contributed in a major way to the ice sheet’s rapid loss of mass.
Because climate models that project the future melting of the Greenland ice sheet do not currently account for these atmospheric patterns, they may be underestimating future melting by about half, said lead author Marco Tedesco from Columbia University’s Lamont-Doherty Earth Observatory.
The study used satellite data, ground measurements, and climate models to analyze changes in the ice sheet during the summer of 2019.
The researchers found that while 2019 saw the second-highest amount of runoff from melting ice (2012 was worse), it brought the biggest drops in surface mass balance since record-keeping began in 1948. Surface mass balance takes into account gains in the ice sheet’s mass — such as through snowfall — as well as losses from surface meltwater runoff.
“You can see the mass balance in Greenland as your bank account,” said Tedesco. “In some periods you spend more, and in some periods you earn more. If you spend too much you go negative. This is what happened to Greenland recently.”
Specifically, in 2019, the ice sheet’s surface mass balance dropped by about 320 billion tons below the average for 1981-2010 — the biggest drop since record-keeping began in 1948. Between 1981 and 2010, the surface mass “bank account” gained about 375 billion tons of ice per year, on average. In 2019, that number was closer to 50 billion tons. And while a gain of 50 billion tons may still sound like good news for an ice sheet, Fettweis explained that it is not, because of another factor: the ice sheet is also shedding hundreds of billions of tons as icebergs break off into the ocean. Under stable conditions, the gains in surface mass balance would be high enough to compensate for the ice that’s lost when icebergs calve off. Under the current conditions, the calving far outweighs the surface mass balance gains; Overall, the ice sheet lost an estimated 600 billion tons in 2019, representing a sea level rise of about 1.5 millimeters.
Before now, 2012 was Greenland’s worst year for surface mass balance, with a loss of 310 billion tons compared to the 1981-2010 baseline. Yet summer temperatures in Greenland were actually higher in 2012 than in 2019 — so why did the surface lose so much mass last year?
Tedesco and co-author Xavier Fettweis, from the University of Liège, found that the record-setting ice loss was linked to high-pressure conditions (called anticyclonic conditions) that prevailed over Greenland for unusually long periods of time in 2019.
The high pressure conditions inhibited the formation of clouds in the southern portion of Greenland. The resulting clear skies let in more sunlight to melt the surface of the ice sheet. And with fewer clouds, there was about 50 billion fewer tons of snowfall than usual to add to the mass of the ice sheet. The lack of snowfall also left dark, bare ice exposed in some places, and because ice doesn’t reflect as much sunlight as fresh snow, it absorbed more heat and exacerbated melting and runoff.
Conditions were different, but no better, in the northern and western parts of Greenland, because as the high pressure system spun clockwise, it pulled up warm, moist air from the lower latitudes and channeled it into Greenland.
“Imagine this vortex rotating in the southern part of Greenland,” Tedesco explained, “and that is literally sucking in like a vacuum cleaner the moisture and heat of New York City, for example, and dumping it in the Arctic — in this case, along the west coast of Greenland. When that happened, because you have more moisture and more energy, it promoted the formation of clouds in the northern part.”
But instead of bringing snowfall, these warm and moist clouds trapped the heat that would normally radiate off of the ice, creating a small-scale greenhouse effect. These clouds also emitted their own heat, exacerbating melting.
Through these combined effects, the atmospheric conditions of the summer of 2019 led to the highest annual mass loss from Greenland’s surface since record-keeping began.
With the help of an artificial neural network, Tedesco and Fettweis found that 2019’s large number of days with these high-pressure atmospheric conditions was unprecedented. The summer of 2012, one of Greenland’s worst years, also saw anticyclonic conditions.
“These atmospheric conditions are becoming more and more frequent over the past few decades,” said Tedesco. “It is very likely that this is due to the waviness to the jet stream, which we think is related to, among other things, the disappearance of snow cover in Siberia, the disappearance of sea ice, and the difference in the rate at which temperature is increasing in the Arctic versus the mid-latitudes.” In other words, climate change may make the destructive high-pressure atmospheric conditions more common over Greenland.
Current global climate models are not able to capture these effects of a wavier jet stream. As a result, “simulations of future impacts are very likely underestimating the mass loss due to climate change,” said Tedesco. “It’s almost like missing half of the melting.”
The Greenland ice sheet contains enough frozen water to raise sea levels by as much as 23 feet. Understanding the impacts of atmospheric circulation changes will be crucial for improving projections for how much of that water will flood the oceans in the future, said Tedesco.
While much of the world is planning for flooding and inundation from changes in sea level, Greenland is facing a much different future. Since the last glacial maximum, about 20,000 years ago, Greenland has been shedding ice, sending it into the surrounding ocean. For much of the world, this has translated into rising sea levels along coastlines, but for Greenland there is a different effect.
Two processes combine to cause sea levels around Greenland to fall as the ice continues to melt. The first is caused by a reduction in the weight of the ice sheet that has for thousands of years been pushing down on the land. As the weight is removed, the land slowly rises back up and coastlines pull up out of the water, a geologic process called isostatic rebound. The second effect is caused by the ocean’s attraction to the large ice sheet. The ice pulls the water towards it with a gravitational tug that raises sea level around Greenland’s coast, but as the size of the ice shrinks, so does this attraction, causing the ocean to fall away and sea level to lower. For both of these reasons, Greenland’s coastlines will rise.
Like many regions of the world, the people of Greenland settled on the waterfront, and the ocean is a major resource used for fishing, hunting and transit. Yet unlike most of the rest of the world, thick ice still dominates the landscape covering over 80 percent of the country, leaving the coastal region as the only area available for settlement. Therefore the change in Greenlanders’ waterfronts will affect every part of their lives, their ports, their travel and the natural habitats they rely on for food.
Quantifying and understanding sea level changes and using this information to help Greenland plan for its future is the goal behind “Greenland Rising/Kalaallit Nunaat qaffappoq,” a National Science Foundation–funded collaborative project of Lamont, the Greenland Institute of Natural Resources (GINR) and local Greenland communities. Our first partner meeting was held in January in Nuuk, Greenland’s capital. Home to about 18,000 people, Nuuk is Greenland’s largest settled area and holds close to one-third of the total population. Located in the southwest of Greenland, Nuuk falls just outside the Arctic Circle and in January experiences about five hours of daylight.
January also brings an annual celebration called Culture Night, when community services and businesses throughout Nuuk open their doors to the residents to visit, explore and learn. The GINR is a favorite Culture Night stop for visitors with the halls filled with touch tanks of crabs, sea urchins and other marine residents, demonstrations of the impacts of sand mining, an augmented reality sand table, rock and mineral displays, large geologic maps of the land, and this year, a first introduction to the local residents of the Greenland Rising/Kalaallit Nunaat qaffappoq project. Over 1,700 community members came through in the three hours of the event, stopping to talk and learn about the project and our new partnership.
For our team it was a wonderful opportunity to share the project goals with the residents and to hear first hand from them what they are witnessing as a result of the impacts of climate change. The project field work will start in Nuuk this spring and summer, providing a chance to speak further with members of the community.
The Greenland Rising/Kalaallit Nunaat qaffappoq Project is a collaboration with The Greenland Institute of Natural Resources and is funded by the National Science Foundation’s Navigating the New Arctic.
A new project will study Greenland’s Helheim Glacier in unprecedented detail, using drones, laser scanners, and high-resolution models to untangle the processes that are driving ice loss in this region.
The research will be carried out by scientist Marco Tedesco from Columbia University’s Lamont-Doherty Earth Observatory and colleagues at partner institutions. It is supported by a multimillion dollar grant from the California-based Heising-Simons Foundation.
The Greenland Ice Sheet plays an important role in global sea level change in a warming world by releasing increasing amounts of freshwater into the ocean. Rapid mass loss from the Greenland Ice Sheet is now responsible for 25 percent of present-day sea level rise, making Greenland the largest single contributor to sea level rise. The majority of ice loss is due to acceleration, retreat, and thinning of glaciers at the ice-ocean interface, through processes that remain poorly understood. The Helheim, on the eastern coast of Greenland, is one of the ice sheet’s largest outlet glaciers and has been rapidly shrinking since 2001. The accelerated retreat of glaciers can exert effects worldwide, from causing sea level rise to adding freshwater to oceans, both of which can affect weather and ocean cycles in the North Atlantic.
The overarching goal of the new project is to improve understanding of the processes occurring at the marine margin of Helheim Glacier, using innovative data-gathering and modeling techniques.
“The project is allowing us to study the Helheim system in its glaciology, atmospheric, and ocean aspects and link them together to provide a picture that will help us understand the mechanisms that drive mass loss and the relative role of atmosphere and ocean on this,” explained Tedesco.
The team will use drones, both above and below water, as well as lasers scanning the ice flow to gather information at a very precise scale.
“We will be running models at ultra-high spatial resolution and combine those outputs with remote sensing to capture what we do well and we don’t. It will be unprecedented and amazing,” said Tedesco.
The high-resolution models will include snowfall, runoff, light reflected off of snow and ice, and other factors responsible for mass loss or gain. “We will also study how the atmospheric changes recently observed in the Arctic and strongly driven by jet stream disruption have been affecting Helheim,” said Tedesco.
The team will spend three to four years collecting comprehensive and parallel measurements of multiple systems to gain an understanding of what drives changes to the Helheim. Additionally, the research will provide an open source database for continued study.
Whereas most federally funded system-based research in the Arctic focuses on the entire Arctic system, this project represents a first in that private donations are supporting a system-based analysis concentrated on a specific region or subsystem.
The team — which includes colleagues from the Woods Hole Oceanographic Institution in San Diego, California; Woods Hole Institute in Woods Hole, Massachusetts; University of California, Irvine; Cold Region Research and Engineering Laboratory, Kansas University; Penn State University; and Oregon State University — performed the first research campaign during the past summer, and is in the planning stages to coordinate next steps.
Rainy weather is becoming increasingly common over parts of the Greenland ice sheet, triggering sudden melting events that are eating at the ice and priming the surface for more widespread future melting, says a new study. Some parts of the ice sheet are even receiving rain in winter—a phenomenon that will spread as climate continues to warm, say the researchers. The study appears this week in the European scientific journal The Cryosphere.
Greenland has been losing ice in recent decades due to progressive warming. Since about 1990, average temperatures over the ice sheet have increased by as much as 1.8 degrees C (3.2F) in summer, and up to 3 degrees C (5.4F) in winter. The 660,000-square-mile sheet is now believed to be losing about 270 billion tons of ice each year. For much of this time, half of this was thought to come from icebergs calving into the ocean, and the other half from melting. But since 2011, direct meltwater runoff has come to dominate, accounting for about 70 percent of the loss. Rainy weather, say the study authors, is increasingly becoming the trigger for that runoff.
The researchers combined satellite imagery with on-the-ground weather observations from 1979 to 2012 in order to pinpoint what was triggering melting in specific places. Satellites are used to map melting in real time because their imagery can distinguish snow from liquid water. Automated weather stations spread across the ice offer concurrent data on temperature, wind and precipitation. Combining the two sets of data, the researchers zeroed in on more than 300 events in which they found the initial trigger for melting was weather that brought rain. “That was a surprise to see,” said the study’s lead author, Marilena Oltmanns of Germany’s GEOMAR Centre for Ocean Research. She said that over the study period, melting associated with rain and its subsequent effects doubled during summer, and tripled in winter. Total precipitation over the ice sheet did not change; what did change was the form of precipitation. All told, the researchers estimate that nearly a third of total runoff they observed was initiated by rainfall.
Melting can be driven by a complex of factors, but the introduction of liquid water is one of the most powerful, said Marco Tedesco, a glaciologist at Columbia University’s Lamont-Doherty Earth Observatory and coauthor of the study. Warm air, of course, can melt ice directly, but is not very efficient by itself, he said. However, warmer air can produce cascading effects. For one, it makes it more likely that atmospheric conditions will pass the threshold where precipitation comes down as rain, not snow. Liquid water carries a great deal of heat, and when it soaks into a snowy surface, it melts the snow around it, releasing more energy. Meanwhile, the warm air that brought the rain often forms clouds, which hem in the heat.
This combination of factors produces a pulse of melting that feeds on itself, and well outlasts the rain itself, often by several days. Moreover, the scientists found that the length of these pulses increased over the decades they analyzed, in cold weather from two days to three, and in the brief summer, from two days to five.
There are longer-term effects, say the study authors. They believe that part of the meltwater runs off, but the rest refreezes in place, morphing normally fluffy, reflective snow on or near the surface into darker, denser masses of ice. This ice absorbs solar radiation more easily than snow, so when the sun comes out, it melts more easily, producing more liquid water, which feeds more melting, in a vicious feedback loop. This, said Tedesco, has led to more and earlier melting in the summer. And because the surface has been hardened into ice, much of that meltwater can more easily flow off the ice sheet toward the sea.
“If it rains in the winter, that preconditions the ice to be more vulnerable in the summer,” said Tedesco. “We are starting to realize, you have to look at all the seasons.”
While rain is hitting increasingly far-flung parts of the ice in summer, winter rainfall so far appears mostly confined to lower elevations in south and southwest Greenland. It is brought in by moist, relatively warm ocean winds from the south, which some communities in other areas call neqqajaaq. These winds may be getting more common due to climate-induced shifts in the jet stream. The elevation of the ice sheet increases further inland and it is thus colder and snowier there; but if average temperatures continue to increase as expected, the line where the moisture comes down as rain instead of snow will rapidly move inward, upward and northward. “The ice should be gaining mass in winter when it snows, but an increasing part of the mass gain from precipitation is lost by melt,” said Oltmanns.
Greenland is not the only place in the far north affected by increasing rain. In recent years, anomalous winter rains have hit the northern Canadian tundra, then refrozen over the surface, sealing in plants that caribou and musk oxen normally forage through the loose snow; in some years, this has decimated herds. And a just-published study from near Fairbanks, Alaska, shows that increasing spring rains are percolating down through the permafrost, thawing it and releasing large amounts of methane, a highly efficient greenhouse gas.
Between 1993 and 2014, global sea-level rise accelerated from about 2.2 millimeters a year to 3.3 millimeters, and much of that acceleration is thought to be due to melting in Greenland. Projections of sea-level rise for the end of this century generally range from two to four feet, but most projections do not yet account for what may happen to the ice in Greenland, nor with the much larger mass in Antarctica, because understanding of the physics is still not advanced enough.
Richard Alley, a prominent glaciologist at Pennsylvania State University, said that the new paper adds to the understanding. “The big picture is clear and unchanged,” he said. “Warming melts ice,” But, he added, the specific processes that will carry this “need to be quantified, understood and incorporated into models. This new paper does important work understanding and quantifying.”
Fiammetta Straneo of Scripps Institution of Oceanography was involved in conceiving the research, and is coauthor on the paper.
Just north of the Arctic Circle in southwest Greenland is a spot at the end of a rugged tundra road where one can step directly off the edge of the earth as most of us know it, and onto the Greenland ice sheet. In summer, hike out a few miles into the jagged, rising surface, and you will hear only wind, the gurgle of running meltwater, and the occasional boom of an ice mass fracturing underfoot somewhere nearby. Amid the 24-hour daylight and seasonal warmth, the ice is rotting. Water ripples in pools and flows through ephemeral streams. In places, the water may plunge and disappear into a moulin–a potentially deadly hole that resonates with the deep-throated thrum of an invisible under-ice river.
Glaciologist Marco Tedesco and a few colleagues walked here this July to study how warming climate is fueling the accelerating decline of the Greenland sheet–the second-largest ice mass on earth. Specifically, he was investigating cryoconites–curious little cylindrical melt holes filled with microorganisms and dust. Often no bigger than a fist, they are part of a much larger natural system that may be magnifying the human forces tearing at the ice.
Tedesco works at Columbia University’s Lamont-Doherty Earth Observatory, home to many ice and snow scientists. A dedicated student of all things frozen, he has a series of snowflakes tattooed on his right bicep, each dedicated to a different person, including his mom. One morning near the start of this latest expedition, he was standing next to a vigorous meltwater stream cutting the ice. “To build an ice sheet is a very long, elaborate process. But it could take really a very short time to melt it all,” he said. “This water flowing here, it has a long memory–it probably froze before Rome was born. What boggles me is the power we humans have to squeeze changes into such a small amount of time. This blanket of ice, it’s like an elephant’s skin. It’s a very powerful dormant animal. But when we wake it up, it has the power to destroy everything it runs through.”
Behind him loomed 660,000 square miles of frozen water. At the edge, it might be only tens of feet thick; in the faraway interior, nearly two miles. If all of it were to melt, it would raise global sea levels about 20 feet. Most scientists think that if this comes to pass due to human-induced climate change, it will take centuries or millennia. But no one really knows. Some of Tedesco’s colleagues recently published geologic evidence that Greenland’s ice did in fact largely disappear some time in the last million years, during one or more past warm periods quite similar to our own.
In any case, sea-level rise is already gnawing at coastal areas and islands around the world, and Greenland is partly responsible. Seasonal melting there has increased by about a third since 1970, in tandem with a 2.2-degree Fahrenheit increase in summer temperatures. It is now losing about 270 billion tons of ice each year. About 70 percent of this loss comes from meltwater runoff; the rest is caused by icebergs discharging directly into the ocean. In 2016, parts of Greenland saw a melt season 20 to 40 days longer than the 1979-2015 average. Largely as a result of this, between 1993 and 2014, yearly global sea-level rise accelerated from 2.2 millimeters to 3.3 millimeters.
Most projections of 21st-century sea-level rise range around two to four feet–but these projections generally do not take into account the melting of Greenland, nor the even bigger mass of Antarctica, because the processes there are still too poorly understood. Considering those factors, some scientists say the rise could be up to 10 feet. That is why it is important to try and figure this out now, says Tedesco.
Climate-related darkening of the ice may be one major factor helping drive the accelerating melt. Windblown dust from natural erosion and human pollution lands on the snowy, naturally reflective surface. In winter, snow covers this up. But because summers are hotter now, come each summer, the surface melts more quickly and extensively, exposing and distilling residue from previous years. Thus the summer surface is becoming progressively darkening. Darker surfaces absorb more solar radiation, so this leads to faster melting. This leads to more darkening. And so on. “It’s a vicious circle,” says Tedesco.
And, it is only part of the circle. Hardy photosynthetic algae and other tiny organisms that specialize in growing within ice and meltwater are basking in the increased warmth, and also building up. To protect themselves from the sun, they develop dark pigments–and this darkens the ice even more. This may be adding greatly to the melting; in fact recent research suggests that such organisms may have now become the primary source of ice darkening. Scientists are only just beginning to appreciate this interplay of ice physics and ice biology. Cryoconites are hot spots of such activity.
Tedesco’s trip began at Kangerlussuaq, a speck of a settlement built around an airstrip that links it to the outside world. In summer the town becomes a staging area for scientists, and for tourists willing to pay the steep cost of getting there for a glimpse of the far north.
Here Tedesco hooked up with Matthew Cooper, a PhD. student at the University of California, Los Angeles, who studies the hydrology of the ice; Dan Bennett, a member of Lamont’s advisory board who had volunteered to come along; and myself. After a couple of days spent sorting out equipment and supplies, we headed out in a rented four-wheel drive pickup along Greenland’s longest road–a rough, 16-mile dirt ribbon following the Akuliarusiarsuup Kuua River, which drains a tongue of the ice sheet.
On the way, Cooper told me that studies by his group have shown the river grows as summer progresses, and melting gathers speed; it also waxes and wanes daily as the sun rises higher in the sky during day and drops lower at night. Near Kangerlussuaq–in Greenlandic, the name means Big Fjord–the river joins other melt streams, and the water flows out said big fjord to the ocean. In recent particularly warm weeks, it has washed out the few crude bridges around town–a real-time, hyperlocal effect of climate change.
Before we even reached the ice, there were reminders that the climate is changing. The road wound through green tundra hills punctuated by raw rock outcrops. In one protected spot we passed a small patch scraggly spruce trees–unremarkable anywhere else, but practically unknown this far north, because it is, or was, too cold. Rumor had it that someone planted these as an experiment some years back. Now they were reaching skyward–not the only place in the Arctic where trees are poised to invade the tundra ecosystem. Tedesco and Cooper’s more immediate concern: polar bears. Normally they live on sea ice, hunting seals, but now the sea ice is melting too, and the 1,000-pound predators are moving onto land–even into the largely lifeless ice sheet, where they have never before been seen. Two had been spotted just weeks before at research stations deep in the ice. One menaced scientists for a day and half before it was shot and killed. We came armed only with pepper spray and air horns.
At first, what appeared to be a low-lying cloud bank loomed on the horizon. This, Tedesco told me, was the Russell Glacier, an outlier of the ice. As we approached, the landscape became ever bigger and grander. Towering, heavily crevassed ice tongues lapped into the river valley’s sides. Creeks gushed out of them and into the river, which raged over rapids and waterfalls.
The road dead-ended at a series of bare hills made of loose dirt and giant boulders–the Russell’s terminal moraine, where advancing ice had previously pushed on the earth like a giant plow. Now, with the glacier in retreat, the ice edge sat low on the other side of the moraine. We made camp nearby. Harried by mosquitoes and distracted by caribou galloping by, the scientists readied instruments and equipment to carry in.
Next day, we hiked over the moraine and descended onto the ice. Here at the edge, it looked more like a dirt sheet than an ice sheet; mud and pebbles coated the crunchy, fast-melting surface. Much of this debris was probably blown off the moraine onto the ice. Jumping the first of dozens of shallow meltwater streams, we walked inward. The ice sloped up in fits and starts. The topography roughened, devolving into hummocks, gullies, hills, pinnacles, cracks, rivulets, puddles, pools and waterfalls. As we ascended, the surface became progressively whiter. It was cold, but the sun was blinding; without sunglasses and sunblock, we would have fried.
After an hour or so, the land behind us was no longer visible. Cracks and meltwater ponds revealed ice that gleamed bright blue–a sign that it had been once deeply buried and heavily compressed, probably over thousands of years. Now the blue ice was exposed to the sun. At one crack, a modest meltwater stream suddenly disappeared into a hole, producing a distant low-frequency gargle. It was a small moulin. “Oooh, that’s creepy,” said Tedesco. “Stay away from that, guys.” Up ahead somewhere, we could hear the distant roar of a much larger one.
We stopped at an irregular swale. Here, the scientists spotted hundreds of circular holes drilled into blue ice. Cryoconites. Ranging from finger- to soccer ball-size, many were filled with crystal-clear meltwater. At the bottoms, a few inches or a foot down, lay a coat of dark ooze. Cooper and Tedesco set up shop here.
Cryoconites exist in icy environments across the world. Biologists have shown the bottom ooze is an admixture of dust, soot and dozens of organisms. These may include photosynthetic algae, bacteria that feed off the dust itself, protozoa, yeasts, microscopic eight-legged rotifers, jellyfish-like tardigrades, and lots of viruses. In many of the cryoconites, small bubbles were forming at the bottoms and ballooning to the surface–methane and other gases produced by this metabolic stew, said Tedesco. He cautioned me not to fill my water bottle from the cryoconites.
No one is exactly sure how they evolve, but somehow, dust and organisms concentrate in one spot. The organisms deposit their byproducts and dead bodies, eventually in enough quantity to form a slime that binds themselves and the dust into a muck that becomes increasingly coherent and efficient at attracting solar energy, melting out a little hole. Little holes become bigger holes. Holes may grow into each other, forming a pond. Liquid in a ponds tends to melt out its sides, and if this progresses outward to a low spot, this spot may become the headwaters of an erosive melt stream.
Tedesco and Cooper had come equipped with sterile bottles, a big syringe and a long spoon to sample the cryoconites’ water and ooze for a biologist at Montana State University. Tedesco deposited a dollop of the ooze on the end of yardstick and offered it to me like a sample of fresh fudge. “Here, you have to feel it!” he said. I did, and it felt like fine, slippery swamp slime. From somewhere nearby came a muffled thunderclap within the ice–slight adjustment of a very large mass, though with no visible results, at least for the moment. Everyone looked at each other, then went back to work.
Tedesco had lugged up a heavy, breadbox-size spectrometer in a backpack. With Bennett holding a laptop to record data, he walked around pointing an attached sensor at the sky, then at the surface, to measure incoming light, and the amount and colors being reflected back. Such measurements are routinely made by satellites on a much larger scale. Comparing ground data with these should help researchers understand how to interpret the satellite imagery, and how small features like cryoconites feed into the overall picture. As a side project, Tedesco is in on a NASA effort to study Mars, where cryoconite-like features are thought to exist. Do they hold liquid water, like those on earth? Do they have living ecosystems? Comparing the light signatures of earthly cryoconites with Martian ones might help address these questions.
Cooper, for his part, had carried up a small drone equipped with a camera. With a portable joystick setup, he launched the helicopter-like machine. It flew a series of grids over the study area with a sound like a giant hummingbird. The images would later be stitched together to make a highly detailed map of the area.
As the evening sun dipped toward the horizon, we made our way back to camp, Tedesco lugging a now-loaded picnic cooler holding water and ooze samples. It was 8pm by the time we returned, and getting quite cold. A young caribou trotted by. After a quick dinner heated up on a portable stove, Tedesco and Cooper were up until midnight checking out their data and recharging batteries.
During the following few days, Cooper tested out an instrument to measure light penetration under the ice. One day, fog rolled in, and we did not venture out; too easy to get lost out there. Occasionally, a few hardy tourists showed up in rented vehicles. Most just stepped briefly onto the ice edge to take selfies, and turned around.
On the final day of fieldwork, we hiked back to the initial study site. This time, Cooper and Tedesco lugged in a 10-foot pole and tripod in order to mount the spectrometer well above the ice. The apparatus was unwieldy, and it took them several hours to wrestle it into position in several spots.
It was getting late, but we decided to do some extra scouting. Following the distant roar of water we had heard the first day, we hiked deeper into the ice. Past a series of ridges, we came upon a clear river running in a blue-ice canyon maybe a hundred feet deep. At one sharp bend, a whirlpool churned. Upstream, to our right, the river wended its way out of sight through a series of loops reminiscent of the Grand Canyon. To our left, it entered a snow-roofed tunnel and abruptly swirled down the lip of a giant, roaring hole. We knew enough not to get too close. It was time to stop doing science, and just stand back in fear, and awe.
As climate warms, the Greenland ice sheet is melting, helping to fuel global sea-level rise. Follow a small team of scientists as they hike onto the sheet to investigate the forces large and small that are demolishing the ice. (All photos: Kevin Krajick) READ THE FULL SCIENTIFIC STORY AND SEE A VIDEO
Earth Institute explorations have led to vitally important new discoveries. In 2017, Gisela Winckler and Joerg Schaefer from the Lamont-Doherty Earth Observatory developed findings about the history of Greenland’s ice sheet that have incited new questions around science’s understanding of the Arctic. Here is the story from Lamont-Doherty’s 2017 annual report. Meanwhile, our 2018 field work season is already in full swing.
A combination of processes determines future sea level rise: thermal expansion of the oceans (the seas swell when water warms); the melting of the ice sheets that cover Greenland in the extreme north and Antarctica in the extreme south; and mountain glacier retreat, the melting of glacial ice on Earth’s mountain ranges. Projections of sea-level rise by the end of this century hover between two and three feet, but many, including predictions compiled and synthesized by the Intergovernmental Panel on Climate Change, do not take Greenland into account. For decades, scientists believed that the Greenland Ice Sheet is relatively stable compared with the vulnerable West Antarctic Ice Sheet.
Two Lamont scientists questioned this assumption about Greenland’s ice and wanted to take a much closer look.
To find answers, geochemists and climate scientists Joerg Schaefer and Gisela Winckler needed to obtain a portion of what is one of Earth’s rarest geologic samples, the only bit of bedrock yet retrieved from the base of the Greenland Ice Sheet, drilled from nearly two miles below the summit of the ice sheet and into the bedrock more than two decades ago.
“It is the most expensive piece of rock ever retrieved on Earth,” said Schaefer. The National Ice Core Laboratory in Lakewood, Colorado, where the core is archived granted the scientists a small portion to subject to geochemical analysis.
Both Schaefer and Winckler specialize in an analytical process that dates samples with cosmogenic nuclides, isotopes produced by tiny particles from outer space that constantly bombard the planet. Specific isotopes are characteristic of exposure to the open sky. Winckler and Schaefer posited that if they could access the surface of Greenland that lies beneath the ice sheet, they could test for the presence of these isotopes and thereby illuminate the history of Greenland’s ice cover, giving scientists a clearer picture of its stability. What they discovered upends aspects of the world’s understanding of polar ice and its impact on the future of the planet.
“The two nuclides we analyzed clearly told us the bedrock that sits underneath the summit of Greenland was exposed for a substantial amount of time,” Schaefer explained. “This simple measurement gets rid of the idea that Greenland is a stable ice cube,” said Schaefer.
“The fact that we measured a certain amount of these cosmogenic nuclides means this whole thing was open to the sky. All of the ice was gone,” said Winckler.
Their analysis shows that Greenland was deglaciated for extended periods during the Pleistocene epoch (from 2.6 million years ago to 11,700 years ago), on the basis of their measurements of cosmic-ray produced beryllium and aluminum isotopes in the bedrock core. Within the rock, the scientists found traces of radioactive beryllium-10 and aluminum-26. The isotopes decay at known rates, and since they cannot be created if the rock is covered with ice, their abundance can be tied to the time when the rocks were exposed. Modelers agree that the region where the core was taken would be one of the last to melt were the ice sheet to disappear. The authors thus concluded that the ice sheet must have been down to less than 10 percent of its current mass when this site was ice-free.
“Unfortunately, this makes the Greenland ice sheet look highly unstable,” said Schaefer. “If we lost it during periods of natural forcing, we may lose it again.” With human-induced warming now well underway, loss of Greenland ice has approximately doubled since the 1990s; during the last four years, by some estimates, it shed more than a trillion tons. Jeff Severinghaus, a paleoclimatologist at the Scripps Institution of Oceanography who was not involved in the study, called the evidence “very direct and incontrovertible.” The study “challenges some prevailing thought on the stability of the ice sheet in the face of anthropogenic warming,” he said. “We can now reject some of the lowest sea-level projections, because the models underpinning them assume continuous ice cover during the last million years.”
Scientists disagree about which potential forces might tip the Greenland ice into quick decline.
These could include water percolating from the surface to lubricate the ice sheet’s base, or massive ice streams discharging icebergs into the ocean.
“That’s the big worry, not today or tomorrow, but that there could be something in the system that is catastrophic. All of a sudden, not gradual, and then the ice is breaking up,” said Winckler.
“Our study steered the entire research field away from the idea that Greenland is a stable ice cube to, ‘oh, my God, Greenland is not stable,’” said Schaefer. “We are missing something big.”
These findings will inform new models of Greenland’s ice. Winckler and Schaefer say their next step is to obtain funding to do a more comprehensive study of the bedrock beneath the ice, to develop a more detailed picture of the past, present, and future of the Greenland Ice Sheet.
Nicolás Young (LDEO), Jason Briner (UB) and an assortment of fellow scientists and graduate students are gearing up to spend a third summer camping along the Greenland ice margin. As part of an ambitious multi-institutional and cross-disciplinary project, NSF-funded Snow on Ice, Young and Briner are collecting lake sediment, rock, water and plant samples that will be used to tease apart linkages between reductions in sea ice on the Arctic Ocean, atmospheric uptake through increased evaporation from the exposed ocean surface and changes in snowfall on the Greenland Ice Sheet. The fieldwork will be centered in southwest Greenland where climate sensitivity during past interglacials was the greatest. The resulting data will be combined with new isotopic ice core work (UW) and updated subglacial topography (UCI), for delivery to two sets of modelers on the project team (UM and NASA JPL) to feed into a set of nested models. Canada’s Geotop and Denmark’s GEUS fill out the partner list.
Explore the photo essay below and read more below to learn about the exciting work of the Snow on Ice Project.
The project goal is to look at the last 8000 years in Western Greenland, spanning back into the last Thermal Maximum when temperatures were approximated at 1-2°C warmer than today and the ice sheet was smaller. It is difficult to constrain the dimensions of an ice sheet that is smaller than present as the traditional markers that are used for evidence are covered over but we will tackle it with the multiple instrument approach described above. The data will be used as a proxy for what might happen in Greenland’s future, addressing with increased certainty whether reductions in Arctic sea ice in the past triggered a feedback loop that caused increased precipitation falling as snow, and resulted in stabilizing the Greenland ice Sheet even in a warming climate.
For more on this project see the Snow On Ice website.
As climate warms, the surface of the Greenland ice sheet is melting, and all that meltwater ends up in seasonal rivers that flow to the sea. At least that is what scientists have assumed until now. Now, a new study has shown that some of the meltwater is actually being soaked into porous subsurface ice and held there, at least temporarily. The finding is part of the first comprehensive on-the-ground study of such a river system. The research could alter calculations of how ongoing melting might fuel global sea-level rise.
Declining ice sheets have been playing an growing role in sea-level rise in recent years. Satellite measurements show that Greenland is losing an average of 260 billion tons of ice a year to the ocean. Something less than half of that appears to come from icebergs falling off the end of the sheet into the sea; the rest is presumably meltwater. But it is not clear exactly how much meltwater actually reaches the sea and where it comes from, because most of the plumbing system is hidden under ice. Lacking direct measurements, computer models have generally used the assumption that meltwater just flows directly out. “It’s always treated as a parking lot, water runs straight off,” said Laurence Smith, a geographer at the University of California, Los Angeles who led the new study.
The study indicates that instead, “the ice acts as a sort of sponge, in which part of the water is trapped,” said Marco Tedesco, a glaciologist at Columbia University’s Lamont-Doherty Earth Observatory and coauthor of the paper. “Instead of behaving like a rigid slab, the ice can rot, creating pores and interstices that are filled with water.” Writing in the Italian newspaper La Repubblica, Tedesco said, “The inclusion of this phenomenon reduces discrepancies between satellite data and model outcomes and may alter Greenland’s projected contributions to sea-level rise.” Tedesco said that meltwater sponged up by various parts of the sheet will eventually make its way to the sea, but the timetable is unknown.
The scientists gathered their data in summer 2015 from a 27-square mile watershed on the ice surface, consisting of a complex system of lakes, tributary creeks and a substantial river. The river culminated at a moulin—a giant hole where the water plunged down, presumably all the way to the rocky bed of the ice. The team mapped the watershed with a drone. Then, anchored to icy stream banks to avoid a fatal fall in, team members took turns lowering instruments down to take hourly readings of the water’s volume, velocity, temperature and depth. They also dropped free-floating sacrificial instruments into the current that took continuous readings until they were swept into the depths of the moulin. The work was documented in a multimedia package by The New York Times.
The scientists determined that up to 430,000 gallons per minute flowed into the moulin. But this did not account for all the water being fed by the watershed. The rest, they concluded, was being soaked into cracks and pore spaces of so-called rotten ice along the route, and probably stored there. Previous models have assumed that there was about 20 to 60 percent more runoff than what the scientists actually measured.
“After eliminating all the other possibilities, we deduced that the disagreement in our data could be attributed to subsurface melting and meltwater storage,” said coauthor Dirk van As, a researcher at the Geological Survey of Denmark and Greenland.
“If there’s a mismatch between observation and model, that means the model is moving the mass in one way or another and not respecting the way things happen in the real world,” said Tedesco.
Tedesco and colleagues plan to return to Greenland this summer to investigate other phenomena, including the widespread growth of algae within the ice that is darkening the near-surface and apparently increasing the ice’s uptake of solar energy. This in turn may be accelerating melting in many areas.
When summer temperatures rise in Greenland and the melt season begins, water pools on the surface, and sometimes disappears down holes in the ice. That water may eventually reach bedrock, creating a slipperier, faster slide for glaciers. But where does it go once it gets there, and what happens to it in the winter? A new study helps answer these questions.
Scientists have been able to observe liquid water at single points by drilling holes, but those observations are limited. An improved technique developed by a graduate student at Lamont-Doherty Earth Observatory and her colleagues is now expanding that view across entire regions, and across seasons for the first time, by making it possible to use airborne ice-penetrating radar to reveal meltwater’s life under the ice throughout the year.
The first results, just published in the journal Geophysical Research Letters, reveal extensive winter water storage beneath the ice. They suggest that glaciers’ response to melting depends not only on the rate at which meltwater flows down, but also on the amount of water stored beneath the ice through the winter, and on the topography and permeability of the land below, said the study’s lead author, Columbia University graduate student Winnie Chu.
“The distribution of meltwater evolves constantly, switching from one location to another,” said Chu. “By knowing how this distribution changes seasonally, we can better understand the spatial linkage between ice and water flow.” Chu said that more meltwater is produced as temperatures rise, and the study suggests that Greenland has the potential to store some of it at the base of the ice. This could potentially mediate the impact of meltwater on summer ice flow by maintaining stable subglacial water pressures through the year, she said.
Greenland’s ice sheet has a wide range of temperatures and impurities that cause the ice to freeze in different ways, and those variations have made it difficult for ice-penetrating radar to identify pockets of water beneath the ice. Chu and her colleagues developed a way to correct for those variations by using 3D thermomechanical ice-sheet models and knowledge of the ice sheet’s chemistry to bring out the reflectivity that indicates water in radar data.
In the study, the researchers describe where water was prevalent inside the ice at the start of the melt season and where it was present at the end of winter in Russell Glacier and neighboring Isunnguata Sermia, in western Greenland. They showed that early in the melt season, most of the meltwater reaching bedrock was along sediment-filled troughs beneath the glaciers. In contrast, during the winter, the bulk of the region’s subglacial water could be seen pooling in higher bedrock ridges, while the lower-elevation troughs were mostly dry.
The scientists suspect that during warmer weather, water pressure opens drainage systems in the ice, allowing meltwater from the surface to flow through to the troughs below. Those channels may close in the winter as less water pours in and water pressure decreases. In the troughs, the sediment-filled floor allows for better drainage. “Any remaining subglacial water then likely continues to seep through groundwater drainage, leaving little wintertime storage at the ice-bed interface,” the authors write. But the ridges are made up of less permeable material, so water can pool on them.
The effect of water is evident in the changing speed of the glaciers during the year. During the 2010 melt season, Russell Glacier flowed more than twice as fast as it did at the end of the following winter, the authors write. The glacier speeds up in early summer, suggesting water pressure rises rapidly there, Chu said. It decelerates quickly at the end of summer, suggesting that the formation of channels in the ice creates more efficient, faster drainage of the meltwater from the glacier bed, the scientists write.
Neighboring Isunnguata Sermia accelerates more slowly. That could be associated with its apparent widespread subglacial water storage capacity, which may be maintaining water pressures through the winter, Chu said. Russell Glacier, in contrast, has less winter water storage and would experience a greater increase in water pressure at the start of the melt season.
“Our findings suggest that the winter subglacial hydrological state could pre-condition the glacier response to additional meltwater in the following summer,” Chu said.
The technique used in the study provides a clearer view of how water moves beneath the ice than any other existing method, said Joseph MacGregor, a glaciologist and geophysicist at NASA-Goddard Space Flight Center who was not involved in the study.
“We have prevailing ideas of how water flows on the surface of ice sheets, through ice sheets, and under ice sheets. What we don’t have are great observations of where that water is beneath the ice most of the time,” MacGregor said. “This result changes that state of affairs. It also demonstrates the value of airborne remote sensing for testing fundamental glaciological hypotheses.”
The paper’s coauthors are Dustin Schroeder of Stanford University; Helene Seroussi of the Jet Propulsion Laboratory at the California Institute of Technology; Steven Palmer of the University of Exeter; and Timothy Creyts and Robin Bell of Lamont-Doherty Earth Observatory. The paper, “Extensive winter subglacial water storage
beneath the Greenland Ice Sheet,” is available online.
In southern Greenland in summer, rivers have been streaming off the ice sheet, pouring cold fresh water into the fjords. Attention has focused on the West Coast, where the majority of the meltwater has been entering the ocean in recent years, but a new study suggests that a greater risk to global climate may actually be coming from the east.
Along the West Coast, meltwater is kept close to shore by the winds that push it northward, the study shows. On the East Coast, however, as much as 60 percent of the meltwater is caught up by the East Greenland Current and ocean eddies that carry it to the Labrador Sea.
Once that cold freshwater is offshore, it can have a powerful effect on the ocean circulation that drives global climate. Recent studies have suggested that the Atlantic Meridional Overturning Circulation—the current that brings warm water up from the tropics toward Greenland and then turns south along North America’s Eastern Seaboard—is slowing and that cold Greenland meltwater may be to blame.
“It’s not like pouring water in a glass that stays where you pour it. It’s more like dumping water in a river—the freshwater will go where the river currents go. In this case, meltwater from the east is flowing toward the Labrador Sea, where it can have a great effect on the global climate,” said study co-author Marco Tedesco, a research professor at Columbia University’s Lamont-Doherty Earth Observatory and adjunct scientist at the NASA Goddard Institute of Space Studies.
Cold, salty water sinks, mixing with the warmer water brought up from the tropics and allowing heat to escape. Cold fresh water, on the other hand, is less dense than salt water and stays at the surface longer. In a 2015 paper, Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research highlighted an abnormally cold region of the North Atlantic and suggested it may be connected with cold Greenland meltwater that appeared to have contributed to the Atlantic Meridional Overturning Circulation slowing in recent decades.
In the new study, published this week in Nature Geoscience, the scientists followed the paths of Greenland’s meltwater using advanced computer modeling with maps of ice-sheet rivers and ocean-going tracers that can track currents. They found that only up to 15 percent of meltwater runoff from Southwest Greenland was being transported into the Labrador Sea, while as much as 50 to 60 percent of meltwater from Southeast Greenland reached the middle of the Labrador Sea.
“The large difference in fate between runoff coming from the West and East coasts of Greenland was quite surprising,” said co-author Renato Castelao of the University of Georgia. “While many studies have quantified nutrient fluxes in meltwater runoff from West Greenland, our results suggest that the northern Labrador Sea will be more influenced by chemical constituents introduced along the East Coast. Constraining fluxes from East Greenland glaciers will be important to quantify the potential impacts of increased runoff on stratification and biogeochemical processes in a region of the ocean that plays a critical role on global climate.”
Greenland’s melt rate is predicted to increase as the planet warms, also affecting sea level rise. On land, Tedesco has also shown how Greenland’s melting is triggering feedback loops, with the effects of melting reducing the ice sheet’s albedo, or reflectiveness, which increases melting. With that in mind, the authors also explored what would happen in the ocean if Greenland’s meltwater rate doubled. Doubling meltwater would more than double the impact on salinity offshore and would keep abnormally cold regions in the Labrador Sea later into winter, they write.
“This is something that needs absolutely to be monitored because of the impact on local ecosystems and the potential feedback of melting glaciers, but also because of the potential impact on a global scale,” Tedesco said.
Former NASA-GISS Director James Hansen, now director of the Climate Science, Awareness and Solutions program at Columbia University’s Earth Institute, waved a red flag last month about the risks that a melting Greenland Ice Sheet could be creating for ocean circulation, warning that increasing meltwater could shut down the Atlantic Meridional Overturning Circulation. If that happened, the North Atlantic would cool and the tropics would continue to warm as CO2 levels increased. The large temperature difference between sea surface and air temperature could drive severe storms along the U.S. East Coast, Hansen warned.
“What happens in Greenland is important, not just for the Arctic but for everything that happens on our planet,” Tedesco said. “You melt something on the East Coast of Greenland, that’s impacting the ocean at both local and global scales, which in turn impacts the climate and life of the Earth.”
The lead author of the new paper is Hao Luo of the University of Georgia. In addition to Tedesco and Castelao, the co-authors include Patricia Yager and Thomas Mote of the University of Georgia; Asa Rennermalm of Rutgers University; and Annalisa Bracco of Georgia Institute of Technology.
Leveraging Local Knowledge to Measure Greenland Fjords: Understanding the Community
Project Background: Changing conditions in Greenland’s northwest glaciers over the last decade have led to a range of questions about water temperature and circulation patterns in the fjords where ocean water meets the glacial fronts. We can use satellites to measure the loss of elevation, the acceleration of ice flow, or the retreat of ice from a glacier, but we can’t use satellite measurements to collect water column temperature profiles. Water column profiles would allow us to better determine how much melt is possible at the glacier connection to the ocean, and help us pinpoint why neighboring glaciers are behaving differently.
The Leveraging Local Knowledge project will work with members of local Greenlandic communities to collect water measurements in the fjords. This will assist in determining if warming Atlantic Ocean water is circulating up through Baffin Bay where it enters the fjords to lap against the frozen glacier footholds, causing them to loosen their hold on the rock below. Alison Glacier (74.37N and 56.08W) is selected as the project focus. Emptying into Melville Bay to the east of Kullorsuaq Island and has been undergoing dramatic change over the last decade.
Our Journey: Our research trip to the small village of Kullorsuaq is a journey that will start 200 kms to the south in the community of Upernavik, located 800 kms north of the Arctic Circle. Flying in on a small 37 seat Dash 7 airplane we overlook a coastline that is lined with glaciers flowing into a bay that is dotted with islands. Most are uninhabited, but Upernavik is home to a population of 1500 permanent residents. An island community, the main employment is fishing with the waterfront sporting a range of both commercial and smaller independent fishing boats.
Upernavik town was established by the Danes in the late 1700s but trade and a religious mission in the early 1800s cemented it as a permanent settlement. The southern end of the island is dotted with a cross covered graveyard representing the religion the Danish settlers brought and the practice of the current community. Christmas, Three Kings Day and other religious holidays are all causes for the community to celebrate. This week the priest will visit Upernavik to celebrate three weddings (Friday and Saturday) and the Confirmation (Sunday). With all such events scheduled for when the priest can preside the parties and celebrations will involve the whole community for days. Celebration and gatherings are a large part of this community’s practice.
The Setting: The icebergs being sloughed from the neighboring glaciers dominate the horizon, littering the waterfront with ice ranging from house-sized blocks to looming masses that appear as large as the neighboring islands. Looking around at the open water it is hard to imagine the origin of these large masses of ice. The closest blocks of ice move during the course of the day, shifting back and forth from north to south and back again. With the shifting and changing of the icebergs the sound of the settling and collapsing of ice is drilled into our consciousness – the sharp crack of the ice as if fractures and the larger canon-like rumble as sections break and fall into the water.
Our local host, a Dane who has lived in Upernavik for 40 years, has fully blended himself into the community where he and his family are well known and liked by both the Inuit and the Danish population. When he learns of our project he observes that in his time here ice cover has significantly changed. He recalls his early years here when the ice in May was so solid in the bay that visiting boats had to drop dynamite on the ice to open a pathway. He points to the open water and the line of haze that hangs on the horizon offering a cause, ‘global heating’.
Other changes have hit Upernavik. We meet a Danish couple who had spent 4 years living in the community, now returning after 30 years to ‘close out their memories’. They spoke with fondness of this lost time when they raised their small children as they worked as a teacher and a nurse. With a team of 10 dogs ‘Lars’ had hunted Greenlandic seal and still had a sharp eye picking a bobbing seal head out on the horizon. They spoke of the people numbering 900 while the Greenlandic dogs had numbered 3000, many times more than the dogs are now. Dogsleds were an important part of that older Upernavik when individual hunting and fishing were the mainstay of the community. While hunting and fishing are still important today Lars notes that things have changed becoming less rugged for an individual. Whether the changes in ice cover have played a part in this is hard to determine.
In our few days here in Upernavik we learn that residents are happy to help, they have networks that reach from one island community to another. Names and contacts are offered freely – “try this person for a place to stay”, “this teacher may be interested in helping you”. It is this networking of local people that we will rely on for the project. Their overall interest in what is happening to their community will be an important part of its long term success.
Leveraging Local Knowledge to Measure Greenland Fjords:
Dave Porter and Margie Turrin are in northwest Greenland working with local community members to collect water column temperature profiles. The project is funded by a Lamont Climate Center grant with support from the NASA Interdisciplinary Program and logistical support from NSF.