Maybe, maybe not. Rationality is not settled, and us philosophers argue about it all the time. :) What you want to say is that group survival is less and less

Maybe, maybe not. Rationality is not settled, and us philosophers argue about it all the time. :) 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.