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Global warming should be brought back below 1C following an unavoidable period of overshooting international temperature targets, if the planet’s frozen regions are to be spared catastrophic melting, a new United Nations-backed report has concluded.
The study found that extensive and lasting losses of snow and ice undermine what it called a “persistent myth”: the belief that exceeding the Paris Agreement’s 1.5C goal, reaching 2C or even 3C, could be manageable or preferable to rapid emission reductions.
The Earth has already warmed by 1.3C since pre-industrial times. Because efforts to curb greenhouse gas emissions and safeguard nature have fallen short, scientists now accept that some degree of overshoot is inevitable as they strive to limit warming to 1.5C by the end of the century.
However, the authors stressed that the severe impact on the cryosphere, the frozen portion of the Earth’s water including all ice and snow, means any period above that threshold must be kept as short as possible. They also called for sufficient carbon dioxide to be removed from the atmosphere to drive long-term warming much lower, ideally below 1C by 2150.
Under current policies, which point to peak warming of around 3C, the report found that almost all near-surface permafrost would thaw, serious and potentially abrupt disruption to ocean circulation would become likely, and ocean acidification would be widespread. Recent research also indicates that sea ice recovers more slowly than previously assumed.
Prepared by 80 scientists convened by the International Cryosphere Climate Initiative (ICCI) and the UN Environment Programme (UNEP), the report found that much of the damage would be irreversible even if temperatures returned to 1.5C, including glacier loss that raises sea levels and endangers water supplies.
James Kirkham, a glaciologist at ICCI and the report’s lead author, described the cryosphere as among the most sensitive parts of the climate system, noting that its loss has consequences for the entire planet. He pointed to one of the largest and deadliest ice-rock avalanches on record this year on the Nepal-China border, which claimed thousands of lives and caused damage equivalent to 10 percent of Nepal’s GDP. He added that Switzerland has lost a fifth of its glacier ice in the past five years, and that thousands of glaciers worldwide are expected to disappear each year over the coming decade.
The report was released as world leaders and diplomats gather in Turkey for COP31, the annual UN climate conference. It documents rapid and accelerating melting across the cryosphere and polar oceans, with consequences ranging from the loss of the Greenland and Antarctic ice sheets, driving sea level rise that threatens hundreds of millions of people, to thawing permafrost releasing further greenhouse gases.
According to the findings, glaciers, which are still adjusting to past warming, would retain only about 70 percent of their present volume over centuries even if long-term warming were reduced to 0.8C. The Greenland and Antarctic ice sheets, now melting roughly six times faster than in the 1990s, would continue to shrink even under scenarios of brief overshoot followed by a return to 1.5C. The scientists concluded that a safe long-term limit for the polar ice sheets is closer to 1.0C, and possibly lower.
Kirkham said snow and ice react quickly to every fraction of a degree of warming, but warned that most of these systems would need centuries or millennia to recover after an overshoot, particularly if tipping points are crossed that make changes effectively permanent.
Last month, a separate UNEP report concluded that global emissions must fall by 18 percent by 2030 and 45 percent by 2035 to give a reasonable chance of keeping warming below 1.7C above pre-industrial levels, finding that no favourable outcomes exist for remaining above 1.5C.
