Most of these systems will take centuries or millennia to recover after overshoot, especially if tipping points are crossed that cause changes to become essentially irreversible. Last month, a UNEP report found the world must cut emissions by 18% by 2030 and by 45% by 2035 to have a good chance of keeping temperatures from rising 1.7C above preindustrial levels.
Scientists urged that every government minister and every fossil fuel executive who has ever succeeded in watering down climate action can look at this report and see how their actions have fundamentally damaged the world we live in.
Switzerland has lost 20% of its glacier ice in the last five years, and thousands of glaciers worldwide are expected to become extinct in the coming decade, every single year. Glaciers would only preserve about 70% of their current volume over a timescale of centuries if long-term heating were brought back down to 0.8C.
The findings expose a persistent myth that overshooting the 1.5C target of the Paris climate agreement to 2C or 3C could be manageable or preferable to urgent emissions cuts, warning that extreme effects on the cryosphere require temperatures to stay above that threshold for as short a period as possible.
The ice sheets covering Greenland and Antarctica, which are melting about six times faster today than in the 1990s, would continue to lose ice even in scenarios where overshoot is brief and temperature rise returns to 1.5C. Current policies will result in 2.8C of global heating, which the report found would reduce the mass of glacier ice to below 10% in the Rockies, Alps, Iceland, and Scandinavia.
The planet has heated by 1.3C since pre-industrial times, and failures to curb greenhouse gas emissions have led scientists to conclude that some level of overshoot is inevitable while trying to keep end-of-century warming to 1.5C. Furthermore, high overshoot expected under current policies with peak temperatures of about 3C would thaw nearly all near-surface permafrost, make severe and possibly abrupt disruption to ocean circulation likely, and lead to widespread acidification.
Sufficient planet-heating carbon should be removed from the atmosphere to bring long-term warming down much further, ideally below 1C by 2150.