Thermometers, at least traditionally, don鈥檛 remember. Mercury expands in response to heat energy, and the red line rises. The temperature falls, the mercury contracts, the line descends. Yesterday鈥檚 measurement has no bearing on today鈥檚.
But even if thermometers can鈥檛 measure it, rising temperatures leave a lasting mark. Forests die, ice sheets melt and species go extinct. Now that the world is within touching distance of 1.5掳C of warming, we are getting hints of the climate chaos we can expect over the coming century. So how bad will it be, and is the damage reversible?
This isn鈥檛 just an abstract question. Last month, the United Nations finally acknowledged that holding warming to 1.5掳C above pre-industrial levels would only be possible if Earth overshoots that threshold, then cools back down by 2100. 鈥淥vershoot, peak, decline鈥� is the new mantra for decision-makers. Let鈥檚 put aside, for the moment, the rather large question of how global cooling on this scale could be delivered. What lasting damage do we risk by overshooting? It is a question scientists are racing to answer.
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There is some good news. Important land carbon sinks like the Amazon rainforest seem to be able to bounce back from short-term climate shocks. We may even be able to resuscitate the AMOC, a vital ocean current, after a climate-induced collapse 鈥� although it won鈥檛 be easy.
When it comes to sea-level rise, we have locked ourselves in for a lot of future pain
But the bad news is that some climate impacts are locked in, even if we clean up our act immediately. As we report, Thwaites glacier in Antarctica looks to be beyond saving, even if ocean-driven melting were halted overnight. In short, when it comes to sea-level rise, we have locked ourselves in for a lot of future pain.
That isn鈥檛 a reason for despair. Once we pass 1.5掳C of warming, we should double down on cutting emissions, not give up. But we should be aware that, even if we do successfully deliver global cooling, we won鈥檛 emerge from the overshoot years unscathed. What we do today matters for tomorrow.
