Even if we already new how to do fusion we couldn't build fusion plants quickly enough to prevent catastrophic warming. Arguably we can't even build fission plants quickly enough for that. The window for fusion has closed, we should've invested forty years ago. Hoping for some breakthrough that allows us to build these fifty times faster than we currently believe we might be able to build them is a very risky maneuver.

Uh, last time I checked we weren't able to do above-unity sustained fusion even at the mega-project level.

Source?

There are companies and research groups in a number of countries currently experimenting with next generation fusion devices which have a new class of superconductor in them as compared to ITER (in essence, they run at a higher cryogenic temperature so need less exotic refrigeration to operate). None have as yet proved their work to be commercially viable (to my knowledge) but there is real work being done.

The United States Patent Office.

And https://www.lockheedmartin.com/en-us/products/compact-fusion...

I admit I myself am highly skeptical of this project... but I welcome it with open arms if its true.