Look, Mars is dead, by Earth standards — literally the best benchmark in the Universe, BTW — and for me the giant irony is that the engineering effort to mitigate climate change here on earth is dwarfed by the cost of creating the most expensive graves in the Universe, only on Mars.
We actually know what the issues here are, it’s just that an influential group want to believe they do not need to be concerned.
In my opinion, they are sadly deluded, but we’ll see.
As a “backup plan”? Meh. Digging deeper might be smarter; also habitats in LEO.
By the time humanity becomes capable enough to be literally unconcerned by such hostile local conditions, then earth is still the better place as we could still survive there better.
We eat earth food; carry earth organisms in our gut and on our skin, we need Earth pH, pressure and temperature and diurnal cycles; we need liquid water and oxygen and trace elements we may not even know of yet; we need protection from UV, ionising radiation, solar weather and God knows what else.
The idea we even have science fiction plans (TM) to reproduce this jewel elsewhere in the Universe is simply beyond fanciful.
As an aside, we would be better off modifying ourselves, if we were really serious.