[inflatableDodo]

>You can't migrate every person on the planet to another one.

I completely agree, none of them are suitable. On the other hand, space habitats built from asteroids are a practical possibility.

>"If the asteroids are ultimately used as the material resource for the building of new colonies, and if by constructing new colonies near asteroids relatively little reaction mass is wasted in transportation, the area of land that is made available on the space frontier can be estimated. Assuming 13 km of total area per person, it appears that space habitats might be constructed that would provide new lands with a total area some 3,000 times that of the Earth. For a very long time at least mankind can look toward resources so nearly inexhaustible that the current frustration of limits to growth can be replaced by a sense of openness and the absence of barriers to further human development."

From the NASA report, 'Space Settlements: A Design Study' - https://settlement.arc.nasa.gov/75SummerStudy/Table_of_Conte...

[kaybe]

We cannot damage the Earth enough for it to be a worse option than space habitats. We simply can't, even if we bomb all of the surface to oblivion, triple the amount of CO2 or even add more toxic gases.

[inflatableDodo]

I'd say that rather depends on the design of the space habitat.

edit - also, while a space economy develops, the initially dangerous and messy environment is part of what will attract many of the first settlers. That and the money. Asteroid mining will be a goldrush.

[kmlx]

any massive planetary destruction (like asteroid strike) will solve this for us.