Cryosphere faces permanent damage when world overshoots 1.5C, scientists warn
Earth's icy regions face dangerous melting that could become permanent if global temperatures overshoot 1.5C, according to a UN report by 80 scientists.
Earth's icy regions face such dangerous melting that global heating should be brought back below 1C after an inevitable period of overshooting global temperature targets, a UN report has found. The planet has already heated by 1.3C since pre-industrial times, and scientists conclude some level of overshoot is inevitable as they fight to keep end-of-century warming to 1.5C.
Permanent and widespread losses of snow and ice expose a "persistent myth" that overshooting the 1.5C target of the Paris climate agreement – to 2C or 3C – could be manageable or even preferable to urgent cuts to emissions, the report found.
The high overshoot expected under current policies – with peak temperatures of about 3C – would thaw nearly all near-surface permafrost, make "severe and possibly abrupt" disruption to ocean circulation likely, and lead to widespread acidification, the report found.
Irreversible consequences
The report, written by 80 scientists brought together by the International Cryosphere Climate Initiative (ICCI) and the UN Environment Programme (UNEP), found much of the damage would be permanent even if global temperatures were brought back down to 1.5C, such as glacier melt raising sea levels and threatening water security.
The cryosphere is "one of the most sensitive components of the climate system", and the consequences of its loss affect the whole planet.
This year, one of the largest and most deadly ice rock avalanches was recorded on the Nepal-China border, killing thousands and leaving damage equivalent to 10% of Nepal's GDP. Switzerland has lost 20% of its glacier ice in the last five years, and thousands of glaciers worldwide are expected to become extinct in the coming decade.
Accelerating melting
The report documented rapid and accelerating melting of the cryosphere and polar oceans, with damages ranging 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 would only preserve about 70% of their current volume over centuries if long-term heating were brought back down to 0.8C, the report found. Meanwhile, the ice sheets covering Greenland and Antarctica, 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 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.
Regional impacts
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.
Every government minister and every fossil fuel executive who's ever succeeded in watering down climate action can look at this report and see how their actions have fundamentally damaged the world we live in.
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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