Take for example the great oxidation event happening 2.5 billion years ago. As oxygen excreting algae began to take over methane producing organisms, oxygen started to build up in the atmosphere - first slowly, as there were lots of stuff to oxidize, like methane and iron. Eventually, these naturals sinks were saturated and oxygen levels reached the critical toxic point for the other species, leading to a runaway die-off where more and more oxygen was released and methane - a strong green house gas - rapidly disappeared from the atmosphere. This shock was so massive it produced the 400 million year Huronian glaciation - a whole planet freeze unlike any since.
So I have full faith life on Earth will eventually restore the feedback loops and get the temperatures back in the sweet spot. I have less faith that this will happen soon, or that most species, humans included, can survive such a massive transition event.
Or just broadly adapt to the new state of things, historical data suggests that atmospheric CO2 levels did reach ~1000PPM up to the Cretaceous, with complete lack of continental ice sheets and temperate forests at the poles.
The current sweet spot is a sweet spot for us and the ecosystems we grew up in as a species, it's not a life-wide sweet spot.
It's mind-boggling to consider that we increased the CO2 levels from 280 to 410 ppm during the industrial age. We went a quarter of the way to the Cretaceous super-greenhouse of 1000 ppm, with most of the change accumulating in recent decades. And we are accelerating.
It's hard to see how most complex ecosystems would survive that kind of change in just a century or so, evolution is simply not that rapid. Forget moving house, imagine a world where the only functional natural ecosystems are bacterial.
Many breadbasket lands are also fairly low-lying. The northern china plain is mostly under 50m. Even if it doesn't get covered in water, saline intrusion will seriously hurt it, as it's already starting to hurt countries with extensive coastlines and river deltas like Vietnam or Bangladesh.
edited to say:
It's interesting that on a long enough time-line, all life on earth is destined for extinction, e.g. the sun expands and vaporizes the earth. So, in the long run, our technological prowess is likely the only hope for our furry (and not so furry) friends.
A recent comment of a recent article about who's the most responsible:
https://www.theatlantic.com/science/archive/2018/08/nyt-mag-...
This stuff doesn't happen in a year. And we have a bunch of ways of ego-engineering, what's missing is an acute need and the economics/political incentives, which again, an acute need would provide.
Venusians thought that and look at where they are now.
So yes, that is a pretty massive thing, especially happening over a lifetime.
Eventually as the Sun gets brighter, the equilibrium amount of CO2 in the atmosphere is expected to drop below the requirements for plant life, and the Earth will die. By heating the atmosphere, we hasten the arrival of the next glacial cycle, but we are (thankfully) at low risk of starving the biosphere.