I'm not familiar with the "final catastrophe" scenarios. Unless what is meant by that is that if CO2 emissions are not reduced to a certain level by a certain date, it becomes too late to avoid arriving at a point in global warming that results in the predicted conditions that are said will result from unchecked global warming. I'm not familiar with any thoughts that suggest actual extinction of Homo sapiens. I just came across this page, which seems like a handy breakdown of the expected results from the degree of global warming going unchecked:
https://www.ucsusa.org/our-work/global-warming/science-and-impacts/global-warming-impacts
I see sea level rise where I live. One result is the disappearance of our salt marshes, as they can't really exist if they're drowned. We see southern fish species moving into our waters, and lobsters, which prefer cold water, declining here. I'm in Rhode Island. But I can't say if these changes are actually linked to global warming, only that these are changes that are visibly happening here.
Elsewhere, the melting of mountain glaciers should have an impact on fresh water resources. And mountain glaciers are melting. That, in turn, would likely lead to the movement of people. Sea level rise itself would lead to movement of people, but it would not be overnight. It would take place over decades, so it would not appear as catastrophic, in the way devastating storms can be catastrophic, and represent "sudden" rather then slow change.
I always felt, and could easily be wrong, that millions of automobiles spewing emmisions into the atmosphere for over 100 years now would be expected to have an impact on the atmosphere. If someone can tell me how that would not be the case, well, I need that education, because otherwise it seems like once Henry Ford applied assembly line technology to the production of automobiles, he made possible something not present beforehand: a technology that added emmisions to the Earth's atmosphere from millions of engines on the road. I don't know how humans do that without consequences. It was not there prior to mass production.
As far as actual warming, it seems like the greatest amount so far is happening in the polar regions. Which does make it "out of sight" for most of us. But it is leading to things like thawing permafrost, and release of methane as a result.
In general, I don't know how these changes happen without consequences. But, I also find it hard to imagine we get to a point where, suddenly, we say "oh my, the global warming warnings were right, what now?" It's like someone will always say "oh, this is just the natural cycle", or "sometimes storms are just really big, that's always been the case". Everything predicted happening over decades of time amounts to a very slow moving catastrophe, which, it seems to me, just makes it hard to recognize it.
Add to that the tendency we have to postpone needed changes, I imagine if the predicted results from global warming are accurate, we won't deal with it until we develop mitigating technology to address it and reverse or mitigate it. Like extracting CO2 from the atmosphere. Which would be a form of adoptation. We will likely need a global response, and since we live in competing self interest nation states, it just seems like that's a lot to expect. We usually wait to act until it's pretty late in the game, and that seems to be the case here.
But the refrain I have often seen here, "the alarmists are saying the world will end in 12 years" is silly. That is not what is being said at all.
We are the X factor in all this. We will have to find ways to mitigate it if we are intent on not finding ways to prevent it. And a global economy dependent on fossil fuels probably means mitigation, not prevention, will be the eventual global response.