It'll never be too late to mitigate even worse effects. Remember that the defeatism is what people who want no change want.
I've read though that if we raise the standard of living of a population, they pollute less, so there might be a self-interest-based solution if we can do it globally.
What you want to say is that group survival is less and less likely the more we prevaricate, and acknowledging the severity of the situation may lead some people, perhaps many, to disengage. I would argue that this can be both rational, on an individual level; a dying man might blamelessly and rationally choose to smoke a cigarette, long after the cancer set in.
What you are noticing, and rightfully afraid of, is that the window of time in which it is rational to act will close long before the heat kills us. Moreover, I can't think of a way of proving that this window has not yet closed, which means that, pending an argument, it might already have elapsed, or just about to.
Scary stuff.
Drastic mitigations need to start now, talking will do nothing. But with people voting in leaders like Trump, nothing will happen. And remember, when gas prices was high during Biden's Admin. ? He did all he could to get them lower, including opening up new oil fields. So both "sides" are to blame.
We should have let the fossil fuel prices rise and force people to change their way of life. Instead our descendants will be force to change in ways that will be far worse then we would have if we started years ago.