[ad_1]
PARIS: The Greenland and Antarctic ice sheets, which contain enough frozen water to raise the oceans to 65 meters, are tracking the UN’s worst-case scenario for sea level rise, researchers said Monday (Aug 31) , highlighting flaws in current climate change models.
The mass loss from 2007 to 2017 due to melting water and melting ice almost perfectly aligned with the more extreme forecasts of the Intergovernmental Panel on Climate Change (IPCC), which predicts that the two ice sheets add up to 40 centimeters ( nearly 16 inches) to global oceans. by 2100, they reported in Nature Climate Change.
Such an increase would have a devastating impact around the world, increasing the destructive power of storm surges and exposing coastal regions that are home to hundreds of millions of people to repeated and severe flooding.
Night view of glaciers in Chiriguano Bay in the South Shetland Islands, Antarctica, on November 8, 2019 (Photo: AFP / Johan Ordonez)
That’s nearly three times more than the mid-range projections from the IPCC’s last Major Assessment Report in 2014, which predicts a 70-centimeter rise in sea level from all sources, including mountain glaciers and expanding water. of the ocean as it warms.
Despite this clear mismatch between the observed reality of accelerating ice sheet disintegration and models that follow those trends, an IPCC special report last year on the icy regions of the planet maintained the same end-of-year projections. century for Greenland and allowed only a small increase. of Antarctica in the scenario of the greatest emission of greenhouse gases.
“We need to come up with a new worst-case scenario for the ice sheets because they are already melting at a similar rate to today,” said lead author Thomas Slater, a researcher at the Center for Polar Observation and Modeling at the University of Leeds. he told AFP.
“Sea level projections are essential to help governments plan climate policies, mitigation and adaptation strategies,” he added.
“If we underestimate future sea level rise, these measures may be inappropriate and leave coastal communities vulnerable.”
Map of Antarctica that locates Seymour Island, which registered its highest temperature on February 9 (Infographic: AFP)
Ice sheet losses at the upper end of the IPCC forecasts would by themselves expose some 50 million people to annual coastal flooding worldwide by mid-century, according to research published last year.
INCREASED BALANCE
Total sea-level rise of at least one meter would likely require spending more than $ 70 billion a year on levees and other flood defenses.
Several factors explain why the climate models underlying the UN projections for sea level might have given little importance to ice sheets, according to the new analysis.
Ice sheet models describe well the long-term impact of gradual global warming, which has caused temperatures to rise at the poles much faster than on the planet as a whole.
But they have failed to account for short-term fluctuations in weather patterns that, themselves, are deeply influenced by climate change.
“For Greenland, much of the ice loss is now being driven by surface melt events during hot summers, processes that were not captured in the AR5 simulations,” Slater said, referring to the 2014 IPCC report, the fifth since 1992.
“We need to understand them better to improve our predictions of sea level rise.”
Until the early 21st century, the West Antarctic and Greenland ice sheets generally accumulated as much mass as they shed. The runoff, in other words, was offset by fresh snowfall.
But over the past two decades, the increasing pace of global warming has upset this balance.
Last year, Greenland lost a record 532 billion tons of ice, the equivalent of six Olympic pools of cold, fresh water that flow into the Atlantic every second. This runoff accounted for 40 percent of sea level rise in 2019.
Forecast of the retreat of the Greenland ice sheet. (Graphic: AFP / Laurence Chu)
A new generation of climate models that better reflect how ice sheets, oceans and the atmosphere interact will underpin the next big IPCC report, to be completed next year, Slater said.
In another study published earlier this month in The Cryosphere, a journal of the European Union of Geosciences, Slater and his colleagues calculated that the Earth’s ice masses, including mountain glaciers, the Arctic ice sheet, and both ice sheets, lost nearly 28 trillion tons of mass between 1994 and 2017.
Less than half of that amount contributed to sea level rise. The Arctic ice sheet, for example, forms in the ocean and therefore does not raise sea levels when it melts.
They found that the rate of ice loss has increased by almost 60 percent in that time period.
