Johan Rockström, the director of the Potsdam Institute for Climate Impact Research and one of the world’s foremost climate scientists, warned that the 1.5C target was not like other political negotiations, which can be haggled over or compromised on.
“A rise of 1.5C is not an arbitrary number, it is not a political number. It is a planetary boundary,” he told the Guardian in an interview. “Every fraction of a degree more is dangerous.”
Allowing temperatures to rise by more than 1.5C would vastly increase the risk of irreversible changes to the climate, he said. For instance, it would raise the risk of the Arctic losing its summer ice, with dire knock-on effects on the rest of the climate as the loss of reflective ice increases the amount of heat the water absorbs, in a feedback loop that could rapidly raise temperatures further.