Man-made climate change has triggered massive ice losses in Greenland that cannot be stopped even if the world stopped emitting greenhouse gases today, according to a new study published Monday.
The findings in Nature Climate Change project that it is now inevitable that 3.3 percent of the Greenland ice sheet will melt – equivalent to 110 trillion tons of ice, the researchers said. That will lead to nearly a foot of global sea level rise.
The predictions are more dire than other predictions, although they use different assumptions. While the study did not specify a time frame for the melting and sea level rise, the authors suggested: much of it could take place between now and the year 2100.
“The point is, we have to plan for that ice as if it wasn’t on the ice sheet for the foreseeable future, within a century or so,” said William Colgan, a co-author on the study. the surface ice cap with his colleagues at the Geological Survey of Denmark and Greenland, said in a video interview.
“Each study has larger numbers than the last. It’s always faster than predicted,” Colgan said.
One reason new research seems worse than other findings may be that it’s simpler. It tries to calculate how much ice Greenland must lose when it recalibrates to a warmer climate. By contrast, advanced computer simulations of how the ice sheet will behave in future global emissions scenarios have yielded less alarming predictions.
A rise of one foot in global sea level would have serious consequences. If sea levels along U.S. coasts have risen by an average of 10 to 12 inches by 2050, a recent report from the National Oceanic and Atmospheric Administration shows: the most destructive floods five times as often, and moderate flooding would become 10 times more frequent.
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Other countries — low-lying island states and developing countries, such as Bangladesh – are even more vulnerable. These countries, which have done little to fuel the higher temperatures that are now thawing the Greenland ice sheet, missing the billions of dollars it will have to adapt to the rising seas.
The paper’s lead author, Geological Survey of Denmark, and Greenlandic scientist Jason Box, collaborated with scientists from institutions in Belgium, Denmark, Finland, Norway, the Netherlands, Switzerland and the United States. to assess the extent of ice loss already trapped by human activity.
Just last year, the UN’s Intergovernmental Panel on Climate Change — which is forecasting generally lower numbers for Greenland’s total ice loss by the end of the century — predicted about half a foot of sea level rise from Greenland for the year 2100. That scenario assumed that humans would emit a large amount of greenhouse gases for another 80 years.
In contrast, the current study does not account for any additional greenhouse gas emissions or specify when the melting would occur, making the comparison with the UN report imperfect.
The finding that 3.3 percent of Greenland is in fact already lost represents “a minimum, a lower bound,” Box said. It could be much worse than that, the study suggests, especially if the world continues to burn fossil fuels and as 2012, which sets a record for Greenland ice loss, becomes more the norm.
But that aspect of the study offers hope: Even if more sea-level rise is held than previously believed, cutting emissions quickly to limit warming to nearly 1.5 degrees Celsius (2.7 degrees Fahrenheit) would prevent that. things would get much worse.
Greenland is the world’s largest island and is covered in an ice sheet that, if it were to melt completely, could raise sea levels by more than 20 feet. There’s no question about that — any more than the fact that during the past warm periods in Earth’s history, the ice sheet was much smaller than it is today. The question has always been how much ice will thaw as temperatures rise — and how quickly.
Melt rates have been increasing over the past two decades, and Greenland is the largest ice-based contributor to the rate of global sea level rise, surpassing contributions from both the larger Antarctic ice sheet and mountain glaciers around the world. Greenland is located in the Arctic, which is warming a lot faster than the rest of the world.
Higher Arctic temperatures cause large amounts of ice on Greenland’s surface to thaw. As the island’s oceanfront glaciers are shedding massive icebergs at an accelerating pace, it’s this surface melt—which translates into flowing glacial rivers, disappearing lakes, and giant waterfalls disappearing into crevasses—that’s what causes the greatest ice losses.
In the past, scientists have tried to determine what Greenland’s continued melting means for global sea levels through complex computer simulations. They model the ice itself, the ocean around it and the future climate based on different emission trajectories.
Overall, the models have yielded modest numbers. For example, according to the latest IPCC assessment, Greenland’s most “probable” loss by 2100 under a very high emissions scenario equates to about 5 inches of sea level rise. This represents the disappearance of about 1.8 percent of Greenland’s total mass.
Most models and scenarios produce something much lower. In a low-emissions scenario, which the world is now trying to achieve, the IPCC report suggests that Greenland would contribute only a few centimeters to sea-level rise by the end of the century.
The new research “obtains high marks compared to other studies,” said Sophie Nowicki, a Greenland expert at the University at Buffalo who contributed to the IPCC report. However, Nowicki noted that one of the reasons the number is so high is that the study considers only the last 20 years — which have seen strong warming — as the current climate to which the ice sheet is now adapting. Taking a 40-year period would yield a lower result, Nowicki said.
“This committed number is not well known and actually quite difficult to estimate, due to the ice sheet’s long response time scale,” Nowicki said.
Box, for his part, argues that the models on which the IPCC report is based are “like a facsimile of reality,” without enough detail to show how Greenland is really changing. Those computer models have sparked considerable controversy of late, with one research group complaining that they are not adequately tracking Greenland’s current, high ice loss.
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In Greenland, the processes that cause ice loss from large glaciers often take place hundreds of meters below the sea’s surface in narrow fjords, where warm water can shoot into the submerged ice in complex movements. In some cases, these processes may simply be too small a scale for the models to capture.
Meanwhile, while it’s clear that warmer air is melting the surface ice sheet, the effects of all that water running off the ice sheet — and sometimes through and under it — raise additional questions. Much of the water disappears into crevices called moulins and travels through invisible paths through the ice to the sea. To what extent this causes the ice itself to become slippery and swing forward is still up for debate and may be on a finer scale than what the models capture.
“Individual moulins, they’re not in the models,” Colgan said.
The new research assesses the future of Greenland through a simpler method. It tries to calculate how much ice loss from Greenland is already dictated by physics, given the current Arctic climate.
An ice sheet — like an ice cube, but on a much larger scale — is always melting or growing in response to the temperature around it. But with a body of ice the size of Greenland—imagine the entire state of Alaska covered in ice one to two miles thick—the adjustment will cost a fortune. long time. This means that a loss can be almost inevitable, even if it hasn’t actually happened yet.
Still, the ice sheet will leave clues as it shrinks. As it thaws, scientists believe the change will manifest itself in a location called the snow line. This is the dividing line between the high-altitude, bright white areas of the ice sheet that collect snow and mass even in summer, and the darker, lower areas that melt and release water to the sea. This line moves every year, depending on how hot or cool the summer is, and keeps track of how much Greenland is melting in any given time period.
The new research argues that in the current climate, the average location of the snowline should move inward and upward, leaving a smaller area for ice to accumulate. That would result in a smaller ice sheet.
“What they’re saying is that the climate we already have is burning away the edges of the ice,” said Ted Scambos, an ice sheet expert at the University of Colorado at Boulder, who did not work on the paper.
However, Scambos said: it could take much longer than 80 years for 3.3 percent of the ice sheet to melt: the study says “most of” the change could happen by 2100.
“Much of the change they predicted would happen in this century, but to… [that level of retreat] would take several centuries, maybe more,” he said.
Future ice losses will be greater than that amount if global warming continues to increase — which it will. For example, if the massive 2012 melt year became the norm, it would likely lead to about two and a half feet of committed sea level rise, the study says.
Penn State University professor Richard Alley, an ice sheet expert, said the fact that researchers remain uncertain about how the planet’s ice sheets will change and raise global sea levels shows the need for more research.
“The problems are very challenging, will not be solved by wishful thinking and have not yet been solved by business-as-usual,” he said.
But Alley added that it’s clear that the more we let the planet warm up, the more the seas will rise.
“[The] increase could be a little less than usual projections, or a little more, or a lot more, but not much less,” Alley said.