Until 2000, the Greenland ice sheet accumulated as much mass as it smelt
Greenland’s major ice block saw a record net loss of 532 billion tonnes last year, raising red flags over accelerating sea level rise, according to new findings.
That is equivalent to an extra three million tons of water flowing into global oceans every day, like six Olympic-sized swimming pools every second.
Curving glaciers and streams of meltwater cut through the Greenland ice sheet – as thick as ten end-to-end Eiffel Towers – were the single largest source of global sea level rise in 2019 and accounted for 40 percent of the total, researchers in the journal Communications Earth reported & Environment.
Loss of mass from last year was at least 15 percent above the previous record in 2012, but even more alarming are the long-term trends, they said.
“2019 and the other four years of record losses have all happened in the last decades,” lead author Ingo Sasgen, a glacier scientist at the Helmholtze Center for Polar and Marine Research in Germany, told AFP.
The ice sheet now follows the worst-case-case global warning scenario from the United Nations Advisory Panel on Climate Science, the IPCC, noted Andrew Shepherd, director of the Center for Polar Observation and Modeling at the University of Leeds.
“This means we need to be prepared for an extra ten centimeters or so of global sea level rise by 2100 from Greenland alone,” said Shepherd, who was not involved in the study.
Draw coastlines of the world
If all of Greenland’s ice sheets melted, it would lift worldwide oceans by seven meters (23 feet).
Even a more modest rise of a few meters would redraw the coastlines of the world and make the land occupied today by hundreds of millions of people uninhabitable.
If all of Greenland’s ice sheet melted, it would lift seven oceans worldwide
Until 2000, the Greenland ice sheet – over an area three times the size of France – generally collected as much mass as it smelt.
Runoff, in other words, was compensated by fresh snowfall.
But in the last two decades ago, the accumulation rate of global warming has upset this balance.
The gap is widening at both ends, according to the study, which emerged from nearly 20 years of satellite data.
Changes in weather patterns – also a result of climate change – have resulted in less cloud cover, and therefore less snow. These high pressure systems have also resulted in more, and warmer, sunny days, accelerating the loss of mass.
In 2019, the ice sheet lost a total of 1.13 trillion tons, about 45 percent of glaciers that slip into the sea, and 55 percent of molten ice, Sasgen said. It received about 600 billion tons by precipitation.
A study in the same journal last week concluded that Greenland’s ice sheet has passed a “tipping point”, and is now doomed to disintegrate, although on what time scale is unknown.
‘Alarm bells ring’
Sasgen says it’s too early to know if we’ve reached a point of no return, but agrees that the ice sheet will likely continue to lose mass, even in colder years.
“But that does not mean that trying not to limit heating does not make sense,” he added.
Forecast retreat from the Greenland ice sheet
“Every decimal degree you store in terms of warming will store a certain amount of sea level rise, both in size and speed.”
At the other end of the world, the West Antarctic ice sheet – which still has six meters of sea level rise – is similarly thought to be rocking at a tipping point, with many experts convinced that it has already been passed.
Scientists not involved in the study were not surprised by the findings, but expressed concerns.
“The ice sheet has lost ice every year for the past 20 years,” said Twila Moon, a research scientist at the University of Colorado.
“If everyone’s not already ringing their alarm bells, they should be now.”
Stuart Cunningham, an oceanographer from the Scottish Association for Marine Science, warned of the potential impact on North Atlantic circulation, a current that keeps northwestern Europe five to ten degrees Celsius warmer than comparable latitudes anywhere in the world.
“Climate models show that this circulation can be eliminated by adding fresh water to the North Atlantic,” he said, noting that this happened during the end of the last ice age.
“This tipping point in the climate system is one of the potential disasters facing us.”
From 1992 to 2018, Greenland lost about four trillion tons of mass, raising the average sea level by 11 millimeters, according to a December 2019 study in Nature.
New research shows that effect of global warming on Greenland ice melts
© 2020 AFP
Citation: Sea level rise accelerates as Greenland ice sheet drops record amount (2020, 21 August) 21 August 2020 retrieved from https://phys.org/news/2020-08-sea-quickens-greenland-ice-sheet.html
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