Not exactly climate change, but still takin care of the environment:
Over a decade ago (!) when I was in grad school, I walked through a park to my office just about every day. A beautiful 20-minute walk. Slightly marred by just how much trash there was on the way.
Eventually I decided to pick up one particularly ugly piece that had been there for weeks. The next day, I picked up another. After two weeks, the path was almost clean -- I'd find a piece once in a while, but not all the time.
From that experience I took on the goal of picking up one piece of someone else's trash in a public place every day. It may seem Sysyphian at first, it actually does help. By having it be routine, i do more through than I can do in that feel-good day of volunteering (which I've also been known to partake in).
I've never mentioned this to anyone until last week, when I mentioned to my partner that in Iqaluit I would bump it up to two pieces given how bad it is here. She hadn't thought of doing anything about it until then; now she's taken on the habit. And so I resolved to talk more about my habit, in hopes it'll spread far and wide.