Earth’s cryosphere is facing potentially irreversible damage if global temperatures exceed 1.5C, according to a report produced by 80 scientists convened by the International Cryosphere Climate Initiative and the UN Environment Programme.
The report says some degree of overshoot is likely as countries try to limit long-term warming, but temperatures should remain above 1.5C for as short a time as possible. It recommends removing enough carbon dioxide from the atmosphere to reduce long-term warming to below 1C by 2150.
Scientists warn that the effects of overshooting would persist even if temperatures later returned to 1.5C. Glacier loss would raise sea levels and threaten water supplies, while melting permafrost could release additional planet-warming gases. The report also points to risks to ocean circulation, widespread acidification and slower-than-expected recovery of sea ice.
Current policies are expected to produce about 2.8C of warming. Under that scenario, nearly all near-surface permafrost could thaw, while glacier ice in the Rockies, Alps, Iceland and Scandinavia could fall below 10% of its current mass. Limiting warming to 1.5C would leave approximately 20% to 35% of that glacier mass.
The Hindu Kush Himalayas would also face major losses. The region’s glaciers provide water for nearly a quarter of humanity, but current policies would leave only 41% of their ice mass. Under a 1.5C scenario, around 83% would remain.
The report says glaciers would preserve only about 70% of their current volume over centuries even if long-term warming were reduced to 0.8C. Greenland and Antarctic ice sheets are currently losing ice around six times faster than in the 1990s and would continue to lose mass even after a brief temperature overshoot.
James Kirkham, a glaciologist at the International Cryosphere Climate Initiative and the report’s lead author, described the cryosphere as one of the climate system’s most sensitive components. He said snow and ice respond quickly to every fraction of a degree of warming, while recovery from overshoot could take centuries or millennia, particularly if tipping points are crossed.
The findings challenge the idea that temporarily exceeding 1.5C and returning to the target later would be manageable. The report says the long-term temperature limit for polar ice sheets is likely much closer to 1C of warming, and possibly lower.
The assessment was released as world leaders and diplomats gather in Turkey for the 31st annual UN climate conference. It follows a UNEP report that said emissions would need to fall by 18% by 2030 and 45% by 2035 to have a good chance of limiting warming to 1.7C above pre-industrial levels.
Sources: The Guardian Science.