I made the transition from fintech to climate (solar) about 5 years ago and am incredibly happy with the decision.
The primary challenge for me was finding a company which was mission-driven, had interesting engineering problems, and had a strong engineering culture. At the time, that combination felt very rare.
Ultimately, software necessarily sits a few steps removed from the tactical changes in climate (energy transition, policy, etc.). That said, I do feel like I'm making a tangible impact on moving the US toward solar and away from carbon-intensive energy.
P.S. I lead the engineering team at Wunder Capital [1]. I'd be happy to chat with anyone interested in moving into climate and/or our open engineering roles.