That isn't true either. Even in the most dark of the global warming scenarios, the Earth will remain habitable by humans.
It's our civilization that is fragile. Something as simple as lack of easily obtainable fresh water will destroy our civilization. And the scariest part is, we may never be able to rebuild it this time. Our civilization was built on cheap oil - the cheap (easy to get to) oil is gone now. That fundamentally limits the size of any civilization that can grow to replace us, and that essentially condemns our descendants to (at best) city-states where life will revolve around the toil of growing food, and occasional warfare.
We have a very short window during which we can access the resources of space - for all practical purposes, limitless resources. But if we screw it up, I can't see how we could get into space again.
Keep in mind, intelligence doesn't necessarily lead to technology. For two easy examples, consider the aboriginal people of Australia. When the made it to Australia, they went farther than any other humans alive at that time - they were by definition the most advanced culture on Earth. Some 60,000 years later, their highest mathmatics had five "numbers": 1,2,3,4 and "a lot" They were stuck in an evolutionary cul de sac. Something similar happened in the Americas.
Bottom line, humans will survive global warming, but we will remain at a level that, today we would consider laughably primative, until the sun finally destroys all life on Earth. And that will be the story of us.
If you want to prevent it, the most important thing we should be doing is exploiting resources in space. That's more important than everything else - more important than healthcare or education, more important than everything.