Work for a PR firm or something similar that supports government action to fight climate change. I know that political marketing probably feels like the dirties

Work for a PR firm or something similar that supports government action to fight climate change. I know that political marketing probably feels like the dirtiest profession out there, but the biggest obstacle to fighting climate change in the present day isn't can't, it's won't. And recent elections have shown the unreasonable (although frankly dangerous) effectiveness of data science in modern politics. As long as we can't beat 'em, we might as well join 'em. If you don't want to do politics, it seems like something related to modeling and/or controlling machinery is probably relevant. Solar concentrators for high-temperature manufacturing (particularly cement/aluminium), ultra-high-temperature electrolysis of steel, and better heat pumps to replace gas heaters, all come to mind as important carbon-reducing technologies that might require a software component, although I can't say exactly how.