One problem is the speed of change, check https://xkcd.com/1732/ https://xkcd.com/1732/ to have an idea. Adaptation needs time, else you get extinction. Very fa

One problem is the speed of change, check https://xkcd.com/1732/ https://xkcd.com/1732/ to have an idea. Adaptation needs time, else you get extinction. Very fast changes on global average temperature are correlated with big extinction events. And we depend on the ecosystem to be more or less as it is, for example to keep having agriculture. Besides that, temperature just doesn't rise without affecting everything else. There are multiple (positive) feedback loops that increase the rate of warming directly (like ice melting reflecting less sunlight) or indirectly (i.e. permafrost thawing do their own carbon emissions) that get triggered once we get past some limits. Once the ball gets rolling things will get much faster, even without our intervention.