[bruce511]

If earth becomes unlivable, then by definition it can no longer support colonies.

The path to making colonies on Mars or the moon self sustaining is not even clear at this point. Starting with the simplest of fundamentals - air, water, food and protection from cosmic radiation. The prospect of growing a technical civilisation on either body, that can develop further without support from Earth is remote.

By contrast, to make earth unlivable basically means nuclear war. Climate change won't do it, biological pandemics won't do it, nor will fossil fuel exhaustion or any other localised event.

On the worst day possible on earth (global radiation aside) its still a million times better to live on than anywhere else.

In terms of global radiation making the world uninhabitable even then tiny, non-sustaining pockets of humanity would survive. At least until their life-support systems failed.

Lastly, I wonder at the need for "the future of mankind" as a goal at all.

[nomel]

> air, water

If all the water on mars were melted, it would cover the planet in 100ft of water [1]. With the safe assumption of any kind of water recycling, and indoor habitats, there's plenty of water on mars, which also means there's plenty of oxygen on mars (along with the 95% CO2). The atmosphere is 3% nitrogen, and 1.6% argon, which means there's plenty of air on mars. You don't have to fill the sky with air, just the buildings.

[1] https://marsed.asu.edu/mep/water#:~:text=Taking%20what%20can....)

[persolb]

That’s all true, but I still think it is a reasonable goal. Having the technology to be self sustaining in another world has the ‘side-effect’ of letting us be self-sustaining on earth… reducing the risks human pose to ourselves.

That said, ‘colonizing’ the artic or shallow ocean floor probably accomplishes most of the benefit for a subset of the cost and risk.

The only real benefit I see to space over the attic is that off worlding mining and production could be a benefit in itself.