AP – The Greenland and Antarctic ice sheets are now losing more than three times as much ice a year as they were 30 years ago, according to a new comprehensive international study.
Using 50 different satellite estimates, researchers found that Greenland’s melt has gone into hyperdrive in the last few years.
Greenland’s average annual melt from 2017 to 2020 was 20 per cent more a year than at the beginning of the decade and more than seven times higher than its annual shrinkage in the early 1990s.
The new figures “are pretty disastrous really”, said study climate scientist at the Danish Meteorological Institute co-author Ruth Mottram. “We’re losing more and more ice from Greenland.”
Study lead author Ines Otosaka, a glaciologist at the University of Leeds in the United Kingdom, said speeded-up ice sheet loss is clearly caused by human-caused climate change.
From 1992 to 1996, the two ice sheets – which hold 99 per cent of the world’s freshwater ice – were shrinking by 116 billion tonnes a year, two-thirds of it from Antarctica.
But from 2017 to 2020, the newest data available, the combined melt soared to 372 billion tonnes a year, more than two-thirds of it from Greenland, said the study in Thursday’s journal Earth System Science Data.
“This is a devastating trajectory,” said United States (US) National Snow and Ice Centre Deputy Lead Scientist Twila Moon, who wasn’t part of the study. “These rates of ice loss are unprecedented during modern civilisation.”
Since 1992, Earth has lost 7.6 trillion tonnes of ice from the two ice sheets, the study found. That’s enough to flood the entire US with almost 0.9 metres of water or submerge France in nearly 15 metres.
But because the world’s oceans are so huge, the melt just from the ice sheets since 1992 still only adds up to a little less than 21 millimetres of sea level rise, on average.
Globally sea level rise is accelerating and melt from ice sheets has gone from contributing five per cent of the sea level rise to now accounting for more than one-quarter of it, the study said. The rest of the sea rise comes from warmer water expanding and melt from glaciers.
A team of more than 65 scientists regularly calculates ice sheet loss in research funded by NASA and the European Space Agency with Thursday’s study adding three more years of data.
They use 17 different satellite missions and examine ice sheet melt in three distinct techniques, Otosaka said, and all the satellites, radar, on the ground observations and computer simulations basically say the same thing – ice sheet melting is accelerating.
Greenland from 2017 to 2020 averaged about 257 billion tonnes of melting a year, compared to just 213 billion tonnes annually from 2012 to 2016. The latest figures also showed what looks like a slowing of melting in parts of Antarctica, which has much more ice than Greenland.
That’s mostly due to smaller and fleeting weather changes and the overall longer-term trend still shows an acceleration of melting in Antarctica, Mottram said.
Antarctica from 2017 to 2020 is still losing about 115 billion tonnes of ice a year, down 23 per cent from earlier in the decade, but overall up 64 per cent from the early 1990s.
“While mass loss from Greenland is outpacing that from Antarctica, there are troublesome wild cards in the south, notably behavior of the Thwaites glacier,” which is nicknamed the Doomsday Glacier, said director of the US snow and ice centre Mark Serreze, who wasn’t part of the study.
Study authors used changes in gravity and in ice height and measured how much snow fell, how much snow melted, how much ice was lost in icebergs calving and eaten away from underneath by warmer water etching through the ice.
“This matters because rising sea levels will displace and/or financially impact hundreds of millions of people, if not billions, and will likely cost trillions of dollars,” said University of Colorado ice researcher and former NASA chief scientist Waleed Abdalati, who wasn’t part of the study.
The study “is not so much surprising as it is disturbing”, Abdalati said in an e-mail.
“A few decades ago, it was assumed that these vast reservoirs of ice changed slowly, but with through the use of satellite observations, field observations and modeling techniques, we have come to learn that ice responds rapidly to our changing climate.”
