The absolute temperature change we are creating with human induced global warming is not the problem here, for the most part. Humans will survive in most places (areas around the Persian Gulf may become uninhabitable if you are poor due to increases in the wet-bulb temperatures). The problem is that the pace of it is so rapid, the biosphere will not be able to adapt fast enough. There will be lots of animals that just go extinct. Which ones and how important they are to us is going to be hard to predict.
I mean, flooding a bunch of highly populated coastal areas is also not good. And the raw heat does kill a lot of kids and elderly people. Will it kill everybody, right now? No. But it does kill people. It's also not just the biosphere, it's stuff like permafrost where a bunch of carbon is locked up. If that all melts, and it's starting to, it accelerates the rate of warming and instead of a 2 degree F increase, it's 4. And then lots more stuff goes very wrong.
It's a huge problem, and we are 100% responsible for it. If you look at natural cycles we're supposed to be getting colder right now, not warmer. Instead we're heating to twice as warm as "warm" cycles would be. Any level of denial is just comically stupid at this point.
Yes, summer gets hot, blah de blah. But the level of hot is hotter and lasts longer than it used to, and the winter colds are less cold and don't last as long. The day to day weather will always have lots of variation, but the overall trend lines over time are extremely clear and they correlate extremely closely with how much carbon we're dumping in the atmosphere.