There's not much one person can do. But there are a lot of us - if lots of people each work on something small it adds up. There are probably plenty of things in your community that have been getting a little better over time for exactly that reason.
When I felt hopeless about politics joining a DSA chapter helped. It makes me feel like I'm doing something helpful, even if it's something small.
What you can do for climate change depends on the opportunities near you. But some ideas might be:
- plant trees
- lobby the school board to install solar panels over a school parking lot
- join an activist group to protest for closure of a local oil refinery
- tell friends an neighbors about benefits of EVs, heat pumps, and other electrification options
- write your elected officials regularly about climate measures you want them to vote for, to thank them when they vote correctly, or to chastise when they don't
I'd focus on one thing instead of trying to do all the things. Working with a local group is ideal.