I usually pick partially funded projects with active updates and thousands of followers with social media presence, like this reforestation project in Rioterra, Brasil https://tree-nation.com/projects/amazonia-rioterra-brazil/up...

The alternative is to dive into it myself like this startup did: https://www.independent.co.uk/climate-change/news/reddit-yis...

I think YC should add sustainability startups/non-profits to their Request for Startups. The combined carbon footprint of YC network is huge.