In the past years I always took part at the Hacktoberfest organized by GitHub and DigitalOcean. The rules are simple, do four (I think in the past it was five) pull-requests to any public projects on GitHub and you'll receive a free t-shirt and some stickers.
This year however, I lack the time to take part too and because I wore the last t-shirts not often enough, I don't need another one that's shipping around the world just to use up more space in my closet.
I took a look at the website though, to see what projects are featured there. I was amazed when I saw a section with projects focused on climate change.
There's also a “topic” on GitHub featuring more projects. Definitely worth taking a look. And if you need a t-shirt and have some time left, maybe contribute to those projects.
One of the projects is the app “Sh**t! I Smoke”. Although I don't smoke it seems like I'm a passive smoker by just breathing.