In short, thanks primarily to carbon pollution, the temperature is changing 50 times faster than it did during the time modern civilization and agriculture developed, a time when humans figured out where the climate conditions — and rivers and sea levels — were most suited for living and farming. We are headed for 7 to 11°F warming this century on our current emissions path — increasing the rate of change 5-fold yet again. By the second half of this century we will have some 9 billion people, a large fraction of whom will be living in places that simply can’t sustain them — either because it is too hot and/or dry, the land is no longer arable, their glacially fed rivers have dried up, or the seas have risen too much. We could keep that warming close to 4°F — and avoid the worst consequences — but only with immediate action.
