The U.N. last month said that, even if countries dramatically slash planet-warming emissions starting right now, the best outcome would be a rise in global temperatures of 1.8 degrees. If they also deploy vast amounts of carbon removal tech to clean up the atmosphere, there’s a chance of getting back to 1.5 degrees after surpassing it — in theory.

In reality, though, greenhouse gas emissions are still rising and the carbon-hoovering technologies needed to achieve that reversal are unproven at scale.

The risk

The collective ambition of national climate plans, already insufficient before the U.N.’s announcement, is even weaker than projected last year. Countries that have been among the strongest proponents of meeting the 1.5-degree target are watering down efforts to achieve it.

But at the same time, many countries (and climate scientists) fear that publicly dumping the rhetoric around 1.5C will open the door to weakening global ambitions even further. Highlighting other possible targets, such as the 1.8C mentioned by the U.N., would be a “slippery slope,” warned one European climate negotiator.

“I do not support the political messaging of keeping 1.5C alive — but on the other hand, I don't want to lose it,” said Johan Rockström, a leading climate scientist and director of the Potsdam Institute for Climate Impact Research.

“Politicians, when they say that, may naively think that we somehow still are on this linear, incremental journey that can simply take us to safety, which is not the case,” he added. “On the other hand, if we scientifically criticize it, the risk is that they do indeed say: ‘OK, let's just drop it and aim for 2 degrees instead,' which would be a big mistake.”