Climate collapse is probably the Great Filter.
The US military used to call climate change a "force multiplier". It turns all the existing stresses up to 11. (Water shortage, ideological and ethnic conflict, great power dick-measuring, etc. etc.)
[Sorry, I can't lay hands on the PDF right now, and I think the research unit was disbanded about 10 years ago, so the report will be difficult to find on the internet. But it was in about 2005 or 2006.]