A UN-backed report warns that even temporarily overshooting the Paris agreement’s 1.5C warming target could cause permanent and widespread losses of glaciers, snow and polar ice sheets. With Greenland and Antarctic ice sheets already melting about six times faster than in the 1990s, the report argues that global temperatures should ultimately be brought back below 1C. The Guardian reports: The report, which comes as world leaders and diplomats converge on Turkey for the 31st annual Cop climate conference, documented rapid and accelerating melting of the cryosphere and polar oceans, with damages that range from the loss of the Greenland and Antarctic ice sheets, driving sea level rises that threaten hundreds of millions of people, to thawing permafrost, which releases more planet-heating gas. Glaciers, which are still responding to historical warming, would only preserve about 70% of their current volume over a timescale of centuries if long-term heating were brought back down to 0.8C, the report found.
Meanwhile, the ice sheets covering Greenland and Antarctica, which are melting about six times faster today than in the 1990s, would continue to lose ice even in scenarios where overshoot is brief and temperature rise returns to 1.5C, the report found. The scientists said a safe, long-term temperature limit for polar ice sheets lies much closer to 1.0C of global heating, and possibly even lower. “Snow and ice respond rapidly to every fraction of a degree of warming,” said [James Kirkham, a glaciologist at ICCI and the lead author of the report. “But most of these systems will take centuries or millennia to recover after overshoot, especially if tipping points are crossed that cause changes to become essentially irreversible.”
Last month, a UNEP report found the world must cut emissions by 18% by 2030 and by 45% by 2035 to have a good chance of keeping temperatures from rising 1.7C above preindustrial levels. It found there were “no good outcomes” of remaining above 1.5C. The cryosphere report found that current policies, which will result in 2.8C of global heating, would reduce the mass of glacier ice to below 10% in the Rockies, Alps, Iceland and Scandinavia. If warming was limited to 1.5C, about 20-35% of the mass would remain. In the Hindu Kush Himalayas, where glaciers are a source of water for nearly a quarter of humanity, current policies will leave just 41% of the ice mass. If warming was limited to 1.5C, 83% would remain.
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