Greenland ice sheet causes sea level to rise nearly a foot


Human-driven climate change is causing massive ice losses in Greenland that cannot be stopped even if the world stops emitting greenhouse gases today, according to the New study Posted Monday.

Findings from the Nature Climate Change report indicate that it is now inevitable that 3.3 percent of Greenland ice cap It will melt – the equivalent of 110 trillion tons of ice The researchers said. This will cause sea level to rise by about a foot.

Forecasts are more risky than other forecasts, although they use different assumptions. The authors suggested that the study did not set a time frame for sea level rise and ice melt Many of them can be implemented between now and 2100.

Said William Colgan, a co-author of the study studying Ice cover from its surface with his colleagues At the Geological Survey of Denmark and Greenland, in a video interview.

“Each study has bigger numbers than the previous one. It’s always faster than expected,” Colgan said.

One reason the new search appears worse than the other results may be that it is simpler. Trying to calculate how much ice Greenland should lose It resets with a warmer climate. In contrast, there are sophisticated computer simulations of how the ice sheet would behave under future global emissions scenarios. It produced less alarming predictions.

height of one foot in Global sea levels will have dire consequences. If sea levels along the coasts of the United States rose by an average of 10 to 12 inches by 2050, a recent report From the National Oceanic and Atmospheric Administration, most destructive flood It will happen five times as often, and the flooding is moderate It will become more than 10 times.

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other countries Low Island States and developing, such as Bangladesh – They are more vulnerable. These countries, which have done little to fuel the rising temperatures that are now melting the Greenland ice sheet, It lacks billions of dollars Take it to adapt to rising seas.

The paper’s lead author, the Geological Survey of Denmark and Greenland scientist Jason Books, collaborated with scientists at institutions in Belgium, Denmark, Finland, Norway, the Netherlands, Switzerland and the United States. To assess how much ice already trapped is lost by human activity.

Just last year, the UN’s Intergovernmental Panel on Climate Change – which generally projects lower figures for total ice loss from Greenland by the end of the century – expected About half a foot of sea level rise from Greenland by 2100 is at the higher end. Suppose this scenario is that humans will export a large amount Greenhouse gases for another 80 years.

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The current study, by contrast, does not take into account any additional greenhouse gas emissions or specify when thawing will occur, Make the comparison with the UN report incomplete.

The finding that 3.3 percent of Greenland had already lost represented “a bottom line, a bottom line,” Box said. The study suggests it could be much worse than that, especially if the world continues to burn fossil fuels and if 2012, which set a record for Greenland ice loss, becomes more like the norm.

But this aspect of the study offers hope: Even if more sea-level rise is secured than previously thought, cutting emissions quickly to limit temperature rise close to 1.5°C (2.7°F) will prevent things from getting worse.

Greenland is the largest island in the world and is covered in a layer of ice that, if completely melted, could raise sea levels by more than 20 feet. This is not in doubt – nor is the fact that in past 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 in the past two decades, and Greenland is Largest single ice-based contributor to the rate of global sea level rise, exceeding contributions from both the greater Antarctic ice sheet and from mountain glaciers around the world. Greenland is located at the North Pole, which is warming a lot Faster than the rest of the world.

Rising Arctic temperatures are melting large amounts of ice on Greenland’s surface. While glaciers bordering the island’s ocean are also dumping massive icebergs at an accelerating pace, it’s this surface melt – which translates into gushing glaciers, disappearing lakes and giant waterfalls that vanish into rifts – that’s causing The biggest ice losses.

In the past, scientists have tried to determine what Greenland’s ongoing melting means for global sea level through complex computer simulations. They model the ice itself, the ocean around it, and the future climate based on different emissions pathways.

Overall, the models produced modest numbers. for example, to me The most recent assessment by the Intergovernmental Panel on Climate Change (IPCC), the “most likely” loss of Greenland by 2100 under a very high emissions scenario, equates to a sea level rise of about 5 inches. This represents the disappearance of about 1.8 percent of Greenland’s total mass.

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Most models and scenarios produce something much less. In the low emissions scenario, which the world is now trying to achieve, the IPCC report notes that Greenland will contribute only a few inches to sea level rise by end of the century.

Sophie Nowicki, an expert in Greenland at the University at Buffalo who contributed to the IPCC report, said the new research “gets high numbers compared to other studies”. Nowicki notes, however, that one reason this number is high is that the study only took into account the past 20 years — which saw extreme temperatures — as the current climate to which the ice sheet is now adapting. Nowicki said taking the 40-year period would lead to a lower result.

“This committed number is not well known and really difficult to estimate, due to the long response time scale of the ice sheet,” Nowicki said.

Boxes, for his part, argues that the models on which the IPCC report is based are “like a mirror image of reality,” without enough detail to reflect how Greenland is really changing. These computer models have sparked a spark big controversy Recently, with one research group imposed on it, it does not adequately track the current high levels of ice loss in Greenland.

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In Greenland, processes leading to ice loss from large glaciers often occur hundreds of meters below sea level in narrow fjords, where warm waters on submerged ice can erupt in complex motions. In some cases, these operations may run at a scale too small for models to capture.

Meanwhile, while hot air is clearly melting the ice sheet from the surface, the consequences of all that water flowing from the ice sheet — and sometimes, through and under it — raise additional questions. Much of the water turns into fissures called mullein, and travels along invisible paths through the ice to the sea. How much this same ice causes it to slide and rush forward remains under debate and may occur on a finer scale than models capture.

“Individual moles, they’re not in the models,” Colgan said.

The new research assesses the future of Greenland in a simpler way. It attempts to calculate how much ice loss from Greenland is actually dictated by physics, given the current arctic climate.

An ice sheet – like an ice cube, but on a much larger scale – is always in the process of melting, or growing, in response to the surrounding temperature. But with an ice body the size of Greenland — imagine the entire state of Alaska covered in ice one to two miles thick — it takes adjusting. long time. This means that the loss can be It is almost inevitable, even if it hasn’t already happened yet.

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However, the ice sheet will leave clues as it shrinks. As the ice melts, scientists believe the change will appear in a place called Snow line. This is the line between the higher elevations and the brighter white parts of the ice sheet where snow and mass accumulate even during the summer, and the darker, lower elevation parts that melt and contribute water to the sea. This line moves each year, depending on how warm or cold the summer is, keeping track of how much Greenland has melted in a given period.

The new research confirms that in the current climate, the average location of the snow line should move inward and upward, leaving a smaller area where ice can accumulate. This will result in a smaller ice sheet.

“What they’re saying is that the climate we’re really in is in the process of burning the edges of the ice,” said Ted Schampos, an ice cap expert at the University of Colorado at Boulder. It didn’t work on paper.

But Scampus said It could take 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.

“A lot of change they expected will happen in this century, but in order to get it [that level of retreat] It will take several centuries, maybe more.

Future ice losses will be greater than that amount if global warming continues to progress – which they will. The study says that if the massive melt year of 2012 becomes the norm, for example, it will likely raise sea levels by two and a half feet.

The fact that researchers are still not sure how the planet’s ice sheets are changing and raising global sea levels shows the need for more research, said Richard Alli, a Penn State University professor and ice sheet expert.

“The problems are very difficult, they will not be resolved by wishful thinking, and they are not yet resolved by business as usual,” he said.

But Alli added that it is clear that the warmer we leave the planet, the higher the seas will rise.

“[The] The height could be a little lower than usual expectations, a little more, or a lot more, but not a lot less,” said Alli.

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