Liability for things like this was traditionally resolved by warfare.

All of us, to the degree that our carbon footprint is above 2 tons a year?

Legally? Almost certainly no one. Ethically? The corporate executives who deliberately covered up evidence of global warming, starting back in the 70s.[1]

1. https://news.harvard.edu/gazette/story/2023/01/harvard-led-a...

Including executives that still refuse to price in the environmental externalities of their business practices.

Why would they do that? That would make their shareholders angry and give their competitors an edge. (No /s)

And don't forget the politicians and media personalities who knowingly or negligently denied that there was even a problem.

They're winning. They have billions of dollars and very cushy lives.

And since we've all known about this for 30+ years, is it still their fault, or is it ours?

It's "their" fault, at least according to Andrew "Twiggy" Forrest, who is one of "them". His view is that if a specific group, of about 1000 powerful people, chose to address climate change, it would be fixed.

https://www.smh.com.au/environment/climate-change/inside-and...

That’s laughable. The number 1 cause of climate change is spread out living. The 0.1+ acre lot with a detached single family home that results in enormous distances required for all the mass to travel.

There is no way people would have or will accept living in Honk Kong style dense living to save the future planet. Hell, they don’t even accept driving smaller vehicles much less changing their whole lifestyle.

What should I have done about it for the past 30 years?

Voted for the environmental candidate every time.

Already did, we still ended up here, clearly that solution didn't work

Persuade others to vote for them?

Already did, we still ended up here, clearly that solution didn't work

Live a life of voluntary poverty?

And if I had done that, how would the climate be today?

Nobody is liable.