. . . if we take action on emissions soon, instituting immediately all of the commitments made in the Paris accords but nowhere yet actually implemented, we are likely to get about 3.2 degrees of warming, or about three times as much warming as the planet has seen since the beginning of industrialization — bringing the unthinkable collapse of the planet’s ice sheets not just into the realm of the real but into the present. That would eventually flood not just Miami and Dhaka but Shanghai and Hong Kong and a hundred other cities around the world. The tipping point for that collapse is two degrees . . .
The upper end of the probability curve put forward by the U.N. to estimate the end-of-the-century, high-emissions scenario — the worst-case outcome of a worst-case path — puts us at eight degrees. At that temperature, humans at the equator and in the tropics would not be able to move around outside without dying.