Cryosphere Faces Permanent Damage When World Overshoots 1.5C, Scientists Warn

A UN-backed report warns that even briefly exceeding the Paris agreement's 1.5C warming target could result in permanent and widespread losses of glaciers, snow, and polar ice sheets. The Greenland and Antarctic ice sheets are currently melting about six times faster than during the 1990s, prompting the report to suggest that global temperatures should ultimately be maintained below 1C.

The report, released as world leaders gather for the 31st annual Cop climate conference in Turkey, highlights the rapid and accelerating melting of the cryosphere and polar oceans, with consequences ranging from sea level rises that threaten hundreds of millions of people to the release of additional greenhouse gases from thawing permafrost.

Glaciers, still reacting to historical warming, would retain approximately 70% of their current volume over centuries if global heating were brought back down to 0.8C, according to the report. However, even in brief overshoot scenarios where temperature rise returns to 1.5C, the ice sheets covering Greenland and Antarctica would continue losing ice.

Scientists assert that a safe, long-term temperature limit for polar ice sheets is closer to 1.0C of global heating, and possibly even lower. James Kirkham, a glaciologist at ICCI and lead author of the report, emphasizes that snow and ice rapidly respond to every fraction of a degree of warming. Nonetheless, most of these systems will take centuries or millennia to recover after overshoot, particularly if tipping points are crossed that render changes essentially irreversible.

A recent UNEP report indicates that the world must reduce emissions by 18% by 2030 and by 45% by 2035 to have a reasonable chance of limiting temperature rise to below 1.7C above preindustrial levels. The report concludes that there are no positive outcomes from remaining above 1.5C. Current policies, which are projected to result in 2.8C of global warming, would reduce glacier ice mass in the Rockies, Alps, Iceland, and Scandinavia to below 10%.

Conversely, limiting warming to 1.5C would preserve about 20-35% of the ice mass. In the Hindu Kush Himalayas, which supply water to nearly a quarter of the global population, current policies would leave only 41% of the ice remaining, whereas limiting warming to 1.5C would retain 83%.