The melting of the ice will have grave consequences for sea level rise and ocean salination, which affects critical ocean currents, unless human societies “sharply curb emissions of greenhouse gases,” scientists warned.
The Greenland ice sheet alone holds enough water to raise the planet’s sea level by 7.4 metres, according to Nasa, and the impacts of climate breakdown are being acutely felt in the Arctic, where temperatures are rising faster than anywhere else in the world.
The team of US scientists used detailed new reconstructions of ancient climate patterns to drive computer models showing how the ice behaves in various circumstances, and compared it with real-world measurements of the sheet’s contemporary and ancient size.
The new model indicates the loss of ice from Greenland by the end of this century is likely to contribute to sea level rises of between 2cm and 10cm.
The findings highlight “just how extreme and unusual projected losses for the 21st century could be”, the researchers said.
“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 of the ice sheet over the past 12,000 years,” said Jason Briner, professor of geology in the University at Buffalo College of Arts and Sciences, who led the study.
“We'll blow that out of the water if we don't make severe reductions to greenhouse gas emissions," he added.
The research team compared different climate scenarios which assume varying levels of greenhouse gas emissions, called representative concentration pathways (RCPs), to model what the human impact could be on the ice sheet.
These include RCP 2.6, which assumes radiative forcing due to greenhouse gases will peak in the mid-21st Century and then decline as emissions sharply drop off, and the “worst case scenario” RCP 8.5, which assumes rapid and unrestricted economic growth along with the rampant burning of fossil fuels.
Prof Briner said: “If the world goes on a massive energy diet, in line with a scenario that the Intergovernmental Panel on Climate Change calls RCP 2.6, our model predicts that the Greenland ice sheet's rate of mass loss this century will be only slightly higher than anything experienced in the past 12,000 years.
“But, more worrisome, is that under a high-emissions RCP 8.5 scenario - the one the Greenland ice sheet is now following - the rate of mass loss could be about four times the highest values experienced under natural climate variability over the past 12,000 years.”
Prof Briner and his colleagues from institutions including Nasa's Jet Propulsion Laboratory, the University of Washington, Columbia University's Lamont-Doherty Earth Observatory (LDEO), and the University of California, said the results “reiterate the need for countries around the world to take action now to reduce emissions, slow the decline of ice sheets, and mitigate sea level rise.”
The multidisciplinary team used state-of-the-art ice sheet modelling to simulate changes to the southwestern sector of the Greenland ice sheet, starting from the beginning of the Holocene epoch some 12,000 years ago and then extending forward 80 years to 2100.
The team was able to test the model's accuracy by comparing their results with historical evidence.
The modelled results matched up well with data from actual measurements of the ice sheet made by satellites and aerial surveys in recent decades, as well as with field work identifying the ice sheet’s ancient boundaries.
Though the project focused on southwestern Greenland, the team said the research indicates changes in the rates of ice loss found there tend to correspond tightly with changes across the entire ice sheet.
“We relied on the same ice sheet model to simulate the past, the present and the future,” said co-author Jessica Badgeley, a PhD student at the University of Washington.
“Thus, our comparisons of the ice sheet mass change through these time periods are internally consistent, which makes for a robust comparison between past and projected ice sheet changes.”
The study represents the first time such timescales have been modelled with confidence, the researchers said.
“We have long timelines of temperature change, past to present to future, that show the influence of greenhouse gases on Earth's temperature,” Prof Briner said.
“Now, for the first time, we have a long timeline of the impacts of that temperature - in the form of Greenland ice sheet melt - from the past to present to future. And what it shows is eye-opening.”
Co-author Nicolás Young, associate research professor at LDEO, said the reliability of the modelling combined with the timescale studied made it hard to pick holes in the results.
He said: “It is no secret that the Greenland ice sheet is in rough shape and is losing ice at an increasing rate.
“But if someone wants to poke holes in this, they could simply ask, 'how do you know this isn't just part of the ice sheet's natural variability?' Well, what our study suggests is that the rate of ice loss for this century will exceed the rate of ice loss for any single century over the last 12,000 years. I think this is the first time that the current health of the Greenland ice sheet has been robustly placed into a long-term context."
Despite the study’s “sobering” findings, the team said it was “vital” to note that the projections show it is still possible for people and countries around the world to make an important difference by cutting emissions.
“Our findings are yet another wake-up call, especially for countries like the US,” Prof Briner said.
“Americans use more energy per person than any other nation in the world. Our nation has produced more of the CO2 that resides in the atmosphere today than any other country.
“Americans need to go on an energy diet. The most affluent Americans, who have the highest energy footprint, can afford to make lifestyle changes, fly less, install solar panels and drive an energy-efficient vehicle.”
The research is published in the journal Nature.
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