Sure, CO2 levels and temperature were a lot higher, 50 million years ago. But the problem for people is that global climate change will mess with stuff that we depend on. Such as the existence of major port cities. And growing food. And more generally, other species can't adapt as fast as our culture could. So we're looking at a major mass extinction. Which we'll also need to deal with, to the extent that we depend on disappearing species.

And sure, we could inject sulfur oxides into the stratosphere. That would create haze that would reflect sunlight. And it wouldn't wash out very quickly. There would still be some acid precipitation impacts, but probably not as bad as we saw in the 60s. However, that would be a huge endeavor, and would take considerable energy.