Maybe we'll get lucky and the fossil fuels will run out before we make the planet completely uninhabitable.
All we have to do is make the planet uninhabitable for us, and the problem ultimately corrects itself.
Hot temperatures are much more difficult to handle than cold temperatures for humans. With proper clothing/goggles/face masks, I've been downright cozy at -43 celsius in northern British Columbia - spent hours completely comfortable. In Dubai, on a hot, humid day in September, I can manage maybe 15 minutes of exertion before I have to escape back to air-conditioning.