[kaybe]

The thing is, even Earth at its worst is still by far the most habitable planet in the system.

The biggest issue we have with climate change is that we and the biosphere are set up for it to be this way, and adaption is slow. We might have to move many cities and the agriculture, and somehow manage with a biosphere that takes many generations to adapt.

[btilly]

The problem comes if, for example, ocean acidification causes a run-away chemical reaction that makes agriculture fail on a large scale, making civilization collapse.

All such possibilities are low. But they aren't 0. Elon's personal judgement is that combined they exceed 1%.