Fusion is very hard. There's been some intriguing progress and I do believe we'll get there – and maybe sooner than many think – but to have a real effect on the climate change timeline I think we'd need to be just about finished with the experimental phase now (if not several years ago) and moving into widespread scale-up. That's just not realistic at this point, unfortunately. So while promising in the long view, I wouldn't bet on it solving any of our near-term problems.

(Edit: and that's ignoring the practical issues of sourcing the required amounts of deuterium / tritium and beryllium, which would rapidly exceed the entire world output under any kind of real scale-up)