* Get a job in cleantech.
I got into the climate-change fighting industry 6 years ago when I became a project engineer for a commercial solar company, then eventually I started my own cleantech software company. By working in the industry, I have had orders of magnitude more impact on fighting climate change than adjusting my lifestyle to be more carbon neutral.
Luckily for the HN crowd, there's a huge need for software and other tech skills (data science, sysadmin, etc.) needed for the energy transition. With the deployment of so much "intermittent" generation like solar and wind, we need tons of software and communications infrastructure to run a new "flexible" grid.
So if you're thinking what can you to help fight climate change, the best thing you can do is get a job in the climate change fighting industry. Start googling around for jobs with climate change keywords ("solar", "wind", "clean energy", etc.). Start showing up to clean energy events (if you live in the bay area, check out my bayareaenergyevents.com). There's so many people in this space who came from other sectors, and it's incredibly easy to move up or start your own company doing some specific thing you think is needed for the fight.