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Earth’s icy regions face severe and dangerous melting, meaning global heating must eventually be brought back below 1C after an inevitable period of overshooting temperature targets, according to a UN report.
Permanent Damage and the Overshoot Myth
The report warns that permanent and widespread losses of snow and ice expose a persistent myth that temporarily exceeding the 1.5C Paris climate agreement target to 2C or 3C could be manageable. With global temperatures already having risen by 1.3C since pre-industrial times and ongoing failures to curb greenhouse gas emissions, scientists have concluded that some level of temperature overshoot is unavoidable.
However, researchers urge that temperatures must stay above the threshold for as short a time as possible. They emphasize that sufficient carbon must be removed from the atmosphere to bring long-term warming down below 1.5C and ideally under 1.0C by 2150. Current policies are expected to produce a high overshoot with peak temperatures reaching approximately 3C, which would thaw nearly all near-surface permafrost, trigger severe ocean circulation disruption, and cause widespread acidification.
Authored by 80 scientists brought together by the International Cryosphere Climate Initiative (ICCI) and the UN Environment Programme (UNEP), the report states that much of the damage would remain permanent even if global temperatures subsequently decline to 1.5C. James Kirkham, a glaciologist at ICCI and lead author of the study, noted that the cryosphere represents one of the most sensitive parts of the climate system, with losses that impact the entire planet.
Kirkham highlighted recent disasters, stating that an ice rock avalanche on the Nepal-China border killed thousands of people and caused damage equal to 10% of Nepal’s GDP. He added that Switzerland has lost 20% of its glacier ice over the past five years, while thousands of glaciers worldwide face extinction in the coming decade.
Melting Polar Ice Sheets and Glaciers
The publication of the report coincides with world leaders and diplomats gathering in Turkey for the 31st annual Cop climate conference. The document documents the accelerating melting of the cryosphere and polar oceans, leading to consequences such as rising sea levels from the shrinking Greenland and Antarctic ice sheets, and thawing permafrost that releases additional greenhouse gases.
Glaciers would preserve only about 70% of their current volume over centuries if long-term heating were successfully brought back down to 0.8C. Meanwhile, the Greenland and Antarctic ice sheets, which are melting roughly six times faster than in the 1990s, would continue losing ice even in scenarios where an overshoot is brief and temperatures return to 1.5C. Scientists determine that a safe, long-term temperature limit for polar ice sheets is much closer to 1.0C of global heating.
Kirkham explained that snow and ice respond rapidly to every fraction of a degree of warming, while taking centuries or millennia to recover after an overshoot, particularly if climate tipping points are crossed. A separate UNEP report released last month indicated that global emissions must drop by 18% by 2030 and 45% by 2035 to maintain a strong chance of keeping temperature rises under 1.7C, noting no positive outcomes exist for remaining above 1.5C.
Regional Impacts and Expert Reactions
Under current policies resulting in 2.8C of global heating, glacier ice mass would drop below 10% in the Rockies, Alps, Iceland, and Scandinavia, compared to retaining 20% to 35% under a 1.5C limit. In the Hindu Kush Himalayas, where glaciers supply water to nearly a quarter of humanity, current policies would leave 41% of the ice mass remaining, whereas a 1.5C limit would preserve 83%.
Bill Hare, CEO of Climate Analytics and a climate scientist who did not participate in the study, described the rapid disappearance of ice sheets, mountain glaciers, sea ice, and the acidification of polar oceans as irreversible on human timescales. Hare stated that every government minister and fossil fuel executive who weakened climate action can view the report as evidence of how their decisions have harmed the world.
