Anders Sandberg, Jason Matheny, and Milan Cirkovic ask "How can we reduce the risk of human extinction?" Some of their answers:
Other measures to reduce extinction risks may have less in common with strategies to improve global security, generally. Since a species' survivability is closely related to the extent of its range, perhaps the most effective means of reducing the risk of human extinction is to colonize space sooner, rather than later.
Citing, in particular, the threat of new biological weapons, Stephen Hawking has said, "I don't think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet." Similarly, NASA Administrator Michael Griffin has noted, "The history of life on Earth is the history of extinction events, and human expansion into the Solar System is, in the end, fundamentally about the survival of the species."
Probably cheaper than building refuges in space would be building them on Earth. Elaborate bunkers already exist for government leaders to survive nuclear war, and the Svalbard Global Seed Vault in Norway protects crop seeds from nuclear war, asteroid strikes, and climate change. Although Biosphere 2 may inspire giggles, functioning refuges that are self-sufficient, remote, and permanently occupied would help to safeguard against a range of hazards, both foreseeable and unforeseeable.