At this point, I think fusion has the best chance
of saving us from ourselves wrt to climate change, so long as the unforeseen consequences aren’t too bad.
It doesn't seem like it's quick enough. We're, at minimum, decades away from it even being built out commonly, and to _really_ save ourselves we should have already replaced a substantial portion of the world's energy generation decades ago.
Yes, this is part of what would need to happen: using a super abundance of essentially carbon-free energy to do geo-engineering on a massive scale (including artificial carbon sequestration).
It might in the future turn out to be more efficient with a "few" reactors than, say, lots of batteries and wind turbines and solar panels, from a resource perspective. But I think not even that will come true, if we optimize stuff enough, which we will have a long time to do before fusion is here.
Fusion would "solve" the climate change issue, but do nothing in regard to all other crises affecting our environment right now (biodiversity collapse, various sources of chemical and particulate pollution, fertilizer runoff...).
On the contrary, unlimited energy would exacerbate the man-made crises we are having today by further pushing the potential impact of man on its environment.