I'm of course quibbling over the definition of "uninhabitable", but again this seems overblown. I concede you're referring to the habitability of Earth by humans, rather than just extremophiles. But still, even with a worst-case scenario, I don't see how this would ever make the Earth completely uninhabitable to humans. Would it make it impossible to sustain billions of humans? Sure, unless they develop some really interesting tech. But I don't see how a mere 12C rise in temperature (or even double that) would make it impossible for humans to survive. Life would probably greatly resemble a Max Max movie, but still, that's different from "uninhabitable". "Uninhabitable" means there's no way for humans to survive at all.

>But I don't see how a mere 12C rise in temperature (or even double that) would make it impossible for humans to survive.

Where is your intuition for this coming from? Note that 12C rise in global temperature is a very different statement than 12C rise in average temperature of where you live. The temperature increase is applied non-uniformly. Also, the volatility in weather scales exponentially with global temperature increase. For example, 1.5C to 2C rise is expected to create 4 times more extreme weather events globally.

>Life would probably greatly resemble a Max Max movie

We don't need a fictional movie to see what life would be like. We are seeing glimpses of it already with these mega weather events hitting areas with a higher risk index such as the recent flooding in Pakistan that resulted in 33 million people impacted, ~600K people displaced, ~2,000 people dead, and ~10 billion USD in damages:

https://en.wikipedia.org/wiki/2022_Pakistan_floods

update to comment: I just saw this article this morning -- a new study on those tipping points I mentioned earlier in our discussion:

https://www.theguardian.com/environment/2022/sep/08/world-on...

2000 people dead is bad of course, but there's 7.5 billion people on the planet right now, so it's not much really.

I really feel like you're looking at a worst-case scenario, comparing it to living in modern civilization, and concluding that modern civilization can't possibly survive such an extreme climactic change, and then concluding that humans will go extinct. I'm sorry, but that simply does not logically follow. Civilization can be destroyed, but this is quite different from all humans going extinct. The Mad Max movies may be fictional, but they do show how humans are able to survive in very extreme conditions, which has been proven countless times in history by humans who really did survive in extreme conditions (go talk to the Innuit for instance). Will 7.5B humans survive in such conditions? Obviously not. Will a few thousand? Quite possibly. It was only a very small number of humans that crossed the land bridge from Africa to the Middle East to populate the rest of the world.

Mad Max is a fictional movie and has nothing to do with reality.

The greatest risk from climate change is not from natural disasters directly like in Pakistan, but the downstream effects of frequent severe weather events and warming of local climates. The loss of life and levels of migration will be much greater when critical infrastructure such as energy production, food production, and clean water supply, are impacted.

Either way, humans going extinct or being reduced by several orders of magnitude is a dire outcome, and we should be doing all we can to prevent it.

There's an enormous difference between total extinction, and civilization being wiped out; that's my whole point. You're trying to conflate the two, and they simply are not the same. For most of human history, there has been zero civilization, and certainly no "critical infrastructure". Humans can go back to that. It won't be pretty, but it is possible, and it's not like extinction.

I think we can agree on the following:

A temperature increase exists where earth will become uninhabitable by humans. One study mentioned above estimates that temperature increase is 12C. It could be higher or lower, but we don't really know without further studies on the topic.

Before reaching that temperature, life on earth will become a lot harsher for all due to the effects of climate change, and we should be doing all we can to avoid those harsher conditions, regardless of what we think the upper bound temperature for humanity to continue existing is.

"mere" is doing some really Herculean lifting in that sentence. most of the terrestrial surface is water. even a 6C mean surface temperature increase means all of our forests are deserts now. 12C mean surface temperature increase is something I don't want to imagine.