> a world where all natural habitat has been completely decimated
That's probably the way we'll have it, but there will be artificial-natural habitat, eg. "reservations", that could grow to even be country-sized or half-continent-sized if we manage resources right. (Though probably they'll be smaller since we're going to have to some pretty large scale heavily-engineered-and-very-unnatural-agriculture to prevent famine in the face of climate degradation.)
The second option sounds somewhat enticing... but it would likely severely diminish speed of technological progress, hence diminish our even-longer-term changes of survival (think encounter and warfare with alien civs etc. - the universe is huge and if we/our-mostly-artificial-descendants survive long enough we'll have to compete with strains of life much more virulent than ourselves today).
If the only thing stopping the structural changes necessary to prevent ecological collapse was a fear of aliens, then I think we'd be doing better.
Also, the kind of technological delay you're talking about there would be a couple of decades at most, when it looks like you're talking about thinking in terms of centuries. If anything, we're slowing down necessary technological advances to maintain the status quo long past the point where it's tenable.
That's probably the way we'll have it, but there will be artificial-natural habitat, eg. "reservations", that could grow to even be country-sized or half-continent-sized if we manage resources right. (Though probably they'll be smaller since we're going to have to some pretty large scale heavily-engineered-and-very-unnatural-agriculture to prevent famine in the face of climate degradation.)
The second option sounds somewhat enticing... but it would likely severely diminish speed of technological progress, hence diminish our even-longer-term changes of survival (think encounter and warfare with alien civs etc. - the universe is huge and if we/our-mostly-artificial-descendants survive long enough we'll have to compete with strains of life much more virulent than ourselves today).