Comment Human-caused climate change has caused massive ice loss in Greenland that could not be stopped even if the world stopped emitting greenhouse gases today, according to a new study published Monday. The findings in Nature Climate Change say it is now inevitable that 3.3 percent of the Greenland ice sheet will melt—equal to 110 trillion cubic meters. tons of ice, the researchers said. This will cause nearly a foot of global sea level rise. Predictions are scarier 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 may take place between now and the year 2100. “The thing is, we have to design this ice as if it wasn’t on the ice sheet in the near future, within a century or so,” William Colgan, a co-author of the study who studies the ice sheet from its surface with his colleagues at the Geological Survey of Denmark and Greenland, he said in a video interview. “Each study has bigger numbers than the last. It’s always faster than anticipated,” Colgan said. One reason the new research seems worse than other findings may simply be that it’s simpler. He is trying to calculate how much ice Greenland has to lose as it recalibrates to a warmer climate. Instead, sophisticated computer simulations of how the ice sheet will behave under future scenarios for global emissions have produced less alarming predictions. A foot rise in Global sea level would have serious consequences. If sea levels along the U.S. coast rose an average of 10 to 12 inches by 2050, a recent report by the National Oceanic and Atmospheric Administration found, the most destructive floods moderate floods would also occur five times more often it would become 10 times more common. ‘They’re not slowing down’: The rise of billion-dollar disasters Other countries — low island nations and developing countries such as Bangladesh — are even more vulnerable. These nations, which have done little to fuel the warmer temperatures now thawing the Greenland ice sheet, lack the billions of dollars that will to adapt to sea level rise. The paper’s lead author, Geological Survey of Denmark and Greenland scientist Jason Box, collaborated with scientists based at institutions in Belgium, Denmark, Finland, Norway, the Netherlands, Switzerland and the United States to estimate the extent of ice loss already locked in by human activity. Just last year, the UN’s Intergovernmental Panel on Climate Change – which generally projects lower numbers for total ice loss from Greenland by the end of the century – predicted about half a foot of sea level rise from Greenland by the year 2100 at the high end . This scenario assumed that humans would emit a large amount of greenhouse gases for another 80 years. The current study, in contrast, does not account for any additional greenhouse gas emissions or specify when the melting will occur, making the comparison with the UN report incomplete. 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 if 2012, which saw record ice loss in Greenland, becomes more like the norm. But this aspect of the study offers hope: even if there is more sea-level rise than previously thought, quickly reducing emissions to limit warming to close to 1.5 degrees Celsius (2.7 degrees Fahrenheit) it will prevent things from getting much worse. Greenland is the world’s largest island and is covered by an ice sheet that, if completely melted, could raise sea levels by more than 20 feet. This is not disputed – nor is the fact that during earlier warm periods of Earth’s history, the ice sheet was much smaller than it is today. The question has always been how much ice will melt as temperatures rise — and how quickly. Melting rates have been increasing over the past two decades, and Greenland is the largest single ice contributor to the rate of global sea-level rise, surpassing the contribution from both the largest Antarctic ice sheet and mountain glaciers around the world. Greenland is in the Arctic, which is warming a lot faster than the rest of the world. Warmer temperatures in the Arctic are causing large amounts of ice on the surface of Greenland to melt. While the island’s oceanfront glaciers are also shedding massive icebergs at an accelerating rate, it’s this surface melting—which translates into gushing rivers of ice, disappearing lakes, and giant waterfalls disappearing into crevasses—that causes the greatest ice losses. In the past, scientists have tried to determine what the ongoing melting of Greenland 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. In general, the models have produced mediocre figures. For example, according to the latest IPCC assessment, the most “likely” loss from Greenland by 2100 in a very high emissions scenario is equivalent 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 currently trying to achieve, the IPCC report suggests that Greenland would contribute only a few inches to sea level rise by end of the century. The new research “gets numbers that are high compared to other studies,” said Sophie Nowicki, a Greenland expert at the University of Buffalo who contributed to the IPCC report. Nowicki noted, however, that one reason the number is so high is that the study only considers the past 20 years—where there has been strong warming—as the current climate to which the ice sheet is now adapting. Taking a 40-year period would have a lower effect, Nowicki said. “This captive number is not well known and is actually very difficult to estimate because of the large scale response time of the ice sheet,” Nowicki said. Box, for his part, argues that the models underlying the IPCC report are “like a facsimile of reality,” without enough detail to reflect how Greenland is actually changing. These computer models have sparked considerable controversy recently, with one research group charging that they do not adequately track Greenland’s current, high levels of ice loss. The alarming message brought by scientists from the ice caves of Greenland In Greenland, the processes that cause the loss of ice from large glaciers often occur hundreds of meters below sea level in narrow fjords, where warm water can move toward the submerged ice in complex motions. In some cases, these processes may simply be played out at too small a scale for the models to capture. Meanwhile, while it’s clear that warmer air is melting the ice sheet from the surface, the consequences of all that water running off the ice sheet — and sometimes, into and under it — raises additional questions. Much of the water disappears into crevasses, called moulins, and travels through invisible paths through the ice to the sea. How much this causes the ice itself to slide and sink forward remains debated, and may be happening on a finer scale than models capture. “Individual moulins, they’re not in the models,” Colgan said. New research assesses Greenland’s future 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 icicle, but on a much larger scale – is always in the process of melting or growing in response to the temperature surrounding it. But with an ice body as large as Greenland — picture the entire state of Alaska covered in ice one to two miles thick — adaptation is needed a long time. This means that a loss can be almost inevitable, even if it hasn’t actually happened yet. However, the ice sheet will leave clues as it shrinks. As it thaws, scientists believe the change will manifest itself in a location called snow line. This is the dividing line between the high altitude, bright white parts of the ice sheet that accumulate snow and mass even during the summer, and the darker, lower parts that melt and contribute water to the sea. This line moves every year depending on how hot or cool the summer is, tracking how much Greenland melts in a given period. The new research argues that in the current climate, the average location of the snow line should be moving inward and upward, leaving a smaller area in which ice could accumulate. This would give a smaller ice sheet. “What they’re saying is that the climate we already have is in the process of burning off the edges of the ice,” said Ted Scambos, an ice sheet expert at the University of Colorado at Boulder. it didn’t work on paper. However, Scambos said it could take much longer than 80 years to melt 3.3 percent of the ice sheet: The study says “most” of the change could happen by 2100. “Many of the changes they predicted would happen in this century, but they will [that level of retreat] it would take several centuries, maybe more,” he said. Future ice losses will be greater than this amount if global warming continues to accelerate — which it will. If the massive melt year of 2012 were to become the norm, for example, that would likely lead to about two and a half feet of bound sea-level rise, the study says. University of Pennsylvania professor Richard Alley, an expert on ice sheets, said the fact that researchers remain uncertain about how the planet’s ice sheets will change and raise global sea levels points to the need for more research. “The problems are deeply challenging, they will not be solved by wishful thinking, and they have not yet been solved by…
