What you can do is:
* a) find someone working on climate change, and help write software for them part-time as a volunteer
* b) brainstorm an idea for a site/app, and build it yourself (and of course post it to HN)
* c) quit your job, join an organization focused on climate change, and do some work
* d) start researching more about climate change until you can make a better choice about a or b or c
If you can't commit a big chunk of time to it, then research good orgs focused on climate change, and donate money to them (or angel invest in them). That's the next best thing you can do.