The economic and political turmoil in the world is unlikely to diminish for many decades, if not centuries, which will make make governments unlikely to commit to or cooperate on any off-world colonisation efforts. This puts the continuation of human civilisation at considerable risk. The next best thing, and something governments may well consider, would be to create places on Earth where humans could survive global catastrophes. There are some examples of this, mostly created during the cold war. The USA, Soviet Union and China created some quite significant underground shelters. But those would protect just a few thousand people for a few months.
What is needed are facilities around the world that could protect millions of people for decades, or longer. Such facilities would need to be deep underground, deep enough to survive even a very close and large asteroid strike, and have no reliance on resupply from the surface.
No matter how large and well designed such a facility is, it could never be permanent. The Earth will still become utterly uninhabitable one day. The humans living there would have to continue researching and planning their eventual evacuation of of the planet. To facilitate this a level of high-technology would need to be maintained. This technology must include the ability for large and regular space launches. Having to live in such an enclosed environment, with the knowledge that the surface is most likely uninhabitable, would focus the minds of scientists and engineers (and probably the entire population, including the government) on the goal of leaving the Earth.
There's an interesting short story on this subject, called 'Under Pindar', about a massive secret cavern deep beneath London. The background to the story can be read here.
|The entrance to a suspected lava tube on the moon|
An interesting study on the potential of lunar lava tubes can be read here.
Perhaps digging should be our first instinct, before we aim outwards?