Humanity won’t do anything about any of this until millions die and mass migrations start happening due to extreme weather events.

We won’t do anything even then.

Well, not anything that’d help, at any rate. The worse things get, the more people will vote for conservatives and populists who will sell them easy solutions, which will likely consist of mass violence and rolling back environmental regulations because they inconvenience their voters. The only thing that will actually help will be the inevitable collapse of industrial society at this scale, but to get there hundreds of millions if not billions will die pointless deaths, especially if nuclear weapons are involved in the collapse.