Look into how miners are making use of stranded methane that is otherwise flared and contributes greatly to global warming (23:00 to 1:11:00 in video below)[1].

[1]https://youtu.be/emc83bQYiF8?t=1358

Also, consider the massive dis-incentivization of consumption that BTC will encourage. The environmental effects are ambiguous, and probably not nearly as bad as mainstream media suggests. It could even be net positive.