If the world turns into the Sahara, we would theoretically just be a planet of Tuaregs, with a population density of zero point zero zero zero something, everyone living in Antarctica, lest we litterally boil into vapor anywhere else.
Or, conversely, if it turns into ice, we´ll live like Inuits, pop dens zero point and-so-on, everyone crammed together alongside Equator.
If the world becomes water world, we´ve seen the movie - it´s a really bothersome existence for the very few involved (apart from those living in the green-promised-land-island)
but yeah - let´s go all out, just to cover everything:
Even if the world turned into Venus, there would be enough fore-warnings, for centuries, that a small elite would make sure they could live there, like that guy in that movie about that planet
Now, don´t get me wrong Crni - none of this means we will function like we function now, I´m not saying "itll be fine" or "it wont be so bad", I´m saying that our species really has no reason to _die out_ - not even if our planet litterally turned into a flaming ball of actual literal fire. We have materials that can withstand fire, and technologies that can create air. Poof! =D
Hell, let´s go further: We could survive even with NO planet, all gone, nothing, no planet anywhere, just empty space. We could sit inside an atmospheric container, eat protein sludge like in The Matrix, just made from recycled people or someshit, or completely synthesized stuff, drink our own pee etc.
And before you go "10 billion people surviving in a space ship, I find that highly unlikely!" I´m not talking about 10 billion or 1 billion or 100 million or 10 million or 1 million or 100 thousand or 10 thousand or 1 thousand
But as a species, we really CAN persist. Without nature shaping us, or affecting us (as a species) much, there´s no real reason we would even "evolve into something else". This surviving elite could be highly genetically manipulated though, in our/their favor of course. We could change ourselves to need very little to survive. We could for example stop moving, stop standing up, we could survive spending energy doing little more than blinking. All this becomes more thinkable in particular if we have centuries of time to prepare - which we probably do - well, elites do. I *do* count the super privileged elites as "human species" after all.
We really can persist for millions of years, depending on our ability to maintain and continue to develop the technology that keeps us alive. Materials etc. I believe in us. I think we can do it! Hundreds of millions.
Also, don´t get me wrong - I feel super-sorry for the rest of the planet, that just had to die away and disappear, like a burp forgotten in space.
(PS: I´m looking forward to having to rehash all of this a couple of weeks or months from now. It´s one of my favorite types of musings!)