A 3°C World Has No Safe Place
Even if greenhouse-gas emissions are slashed, there is still a chance of crashing through the Paris agreement's climate targets. What would that look like?
The caveat is that this estimate includes policies announced but not enacted. A world which follows the policies that are actually in place right now would end up at 2.9°C, according to CAT (the UN Environment Programme, which tracks the gap between actual emissions and those that would deliver Paris, provides a somewhat higher estimate). Almost everyone expects or hopes that policies will tighten up at least somewhat. But any reasonable assessment of the future has to look at what may happen if they do not.
A 3°C world is thus both a pretty likely outcome if nothing more gets done and the worst that might still happen even if things go very well indeed. That makes it worth looking at in some detail, and the result is alarming. Those modelling climate impacts have long argued that they do not increase linearly. The further you go from the pre-industrial, the steeper the rate at which damages climb. And as what was rare becomes common the never-before-seen comes knocking. Judging by the results of specific studies, the differences between 2°C and 3°C are, in most respects, far starker than those between 1.5°C and 2°C.