What Happens After Warming Hits 1.5C? A Guide to Climate Overshoot

Diplomats and world leaders now gathered in Egypt for the annual UN climate summit are tasked with keeping the global average temperature below 1.5°C of warming, in some sense. It is one of the key objectives around which the 2015 Paris Agreement was built, and has therefore become a shorthand for the success of every subsequent climate summit.

Talks at COP26 last year in Glasgow ended with the conference leader saying the 1.5C limit “is alive but its pulse is weak.” Ahead of COP27 in Sharm el-Sheikh, UN-backed scientists on the Intergovernmental Panel on Climate Change contributed to a bleak forecast predicting that the world is likely to surpass the 1.5C mark in the 2030s. Tributes to 1.5C have followed, even though politicians speaking from the ongoing summit in Egypt have not left it for dead.

Former British Prime Minister Boris Johnson said on Monday: “If we maintain the spirit of constructive optimism – the Promethean, the constructive optimism that we saw in Glasgow – then I think we hope to limit the rise in temperature to 1.5%.” can keep it alive.” When he hosted COP26, he often repeated a slogan: “Keep 1.5 alive.”

Every tenth of a degree counts, which is why countries in the Paris Agreement called for “pursuing efforts to keep global average temperature rise below 2C above pre-industrial levels and limit temperature rise to 1.5C”. Codified his plan for In other words, there is no precipitate or event horizon on the other side of the line. It is an organizing principle.

“What’s obviously really important is that the 1.5C limit is a political limit,” says David Keith, a Harvard University physicist and advisor to the Climate Overshoot Commission. exceeds these warming targets. “Whether it matters or not depends on how politically it matters. Not that there is some scientific magic at 1.5C.”

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