Elon Musk, the billionaire founder and CEO of the private spaceflight company SpaceX, wants to help establish a Mars colony of up to 80,000 people by ferrying explorers to the Red Planet for perhaps $500,000 a trip.
(...) we've put all our eggs in one basket. If we were on many worlds and were to mess up down here, there's a way for the human species to continue. I don't for a moment propose that the Earth is a disposable planet, and we have to put enormous efforts into making sure we don't muss up down here. But there is a chance.
If we can build a self sufficient small scale economy which is independent from earth's ecosystem services and industry base - i.e. an independent martian colony - most listed existential risks a martian colony might mitigate cease to be existential. This is since the mechanism of these existential risks is reduction of ecosystem services provided by earth's biosphere triggering a breakdown of our interconnected world economy with subsequent starvation of most people or even a breakdown of our interconnected world economy without significantly reduced ecosystem services.
This obviously applies to: < 20km diameter impactors, (current tech) wars, famine, super volcanoes, (nearly all) climate change scenarios, global computer failure.
It also applyes to: most pandemics (sub 100% lethality or shelter avaiable or some region spared), most supernova scenarios (breakdown of agriculture due to Ozone layer disruption, far away enough to not instantly fry the earth), some bio- and nanoweapons (sub 100% lethality or shelter avaiable or some region spared).
So a Mars colony will only exclusively survive some highly specific and thus unlikely scenarios: A nano-outbreak which can break into an earthbound shelter, but does not spread through space, a very intense GRB which hits earth but not Mars (is this even possible?), an earth impactor large enough to heat the atmosphere to several hundred °C, perhaps some weird physics disaster.
So what we should do to mitigate x-risks is building a self sufficient small scale economy which is independent from earth's ecosystem services and industry base, not ship it to Mars. Though I fear this is not possible at our current tech level.
I've thought the same thing. A big, deep, independent, hermetically sealed, geothermally powered complex under say Iceland or New Zealand gets you most of the x-risk mitigation that a martian colony does.