Scientists assembled by the International Cryosphere Climate Initiative and UN Environment Programme have concluded that permanent and widespread losses of snow and ice will occur if global temperatures exceed the 1.5C Paris climate target, challenging the notion that temporary overshooting could be acceptable.
The planet has already warmed 1.3C since pre-industrial times, with failures to reduce emissions making some degree of overshoot inevitable. However, the report emphasizes that any temperature increase above 1.5C should be kept as brief as possible. Under current policies projecting approximately 3C of warming, nearly all near-surface permafrost would thaw, ocean circulation would face severe disruption, and widespread ocean acidification would occur. The report notes that sea ice recovers more slowly than previously understood.
Damage to glaciers and ice sheets would prove largely irreversible even if temperatures were subsequently reduced to 1.5C. Glaciers worldwide are melting at accelerating rates, with some regions like Switzerland losing 20% of glacier ice in recent years. Current policies would reduce glacier ice mass to below 10% in the Rockies, Alps, Iceland and Scandinavia, compared to 20-35% retention under 1.5C warming. In the Hindu Kush Himalayas, which supply water to nearly a quarter of humanity, ice mass would decline to 41% under current policies versus 83% at 1.5C warming.
The Greenland and Antarctic ice sheets are melting approximately six times faster than during the 1990s and would continue losing ice even under scenarios with brief overshoot periods. Scientists identified a safe long-term temperature threshold for polar ice sheets closer to 1.0C of global heating. The report concludes that sufficient atmospheric carbon removal must occur to bring long-term warming below 1C by 2150.
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