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Moon Colonies I: Overpopulation

Amanda Marcotte has a post about theoretical physicist Stephen Hawking's recent foray into geography, in which Hawking declares that the key to solving our environmental crisis is to colonize space. I generally agree with Marcotte's view (also echoed by Chris Clarke) that overreliance on space colonization is a distraction. Indeed, we can already see the results, as NASA is currently cutting funding for much-needed Earth monitoring satellites in order to find money for space exploration.

In this post I want to deal with one pro-colonization argument that is repeatedly brought up in the comments to Marcotte's post: that it would solve overpopulation. As commenter Ellis Tripp put it:

Transferring a sizeable portion of the Earth’s humans and human-dependant species to Mars would give other species a little more breathing room and make it easier for them to rebound from things like epidemics and natural disasters.

In other words, space can act as a sort of safety valve for overpopulation. I happen to be skeptical of how important population is as a point of attack in solving environmental problems, but I'll set that aside for now. There are two basic ways to think about population growth, and I don't think either of them lend much support to the idea of space colonization as a solution.

The first way -- which has a long history in environmentalism stretching back at least to Malthus (though Malthus drew very different conclusions than his contemporary disciples) -- is that population grows exponentially. Resource constraints form a simple ceiling, and population grows faster and faster until it bumps up against that ceiling. Space colonization, then, would raise the ceiling, adding extraterrestrial resources to our portfolio. We could siphon off Earth's excess population to Mars, then eventually Mars's to Venus, and Venus's to Alpha Centauri ... The problem, of course, is that solving exponential population growth through colonization requires exponential colonization. We'd need to colonize other planets faster and faster to keep up. Even if we could manage that feat, the universe is huge, but it is finite. And the key point made in any ordinary discussion of exponential growth is how quickly exponential growth can overwhelm even the largest-seeming space.

The other way to look at population -- which most demographers agree is more accurate as a description of the contemporary global population -- is logistical, or S-shaped, growth. Population initially rises quickly, but then it slows down and levels off. The Earth's global population passed the steepest point in the 1970s, and most predictions say we're likely to level off around 10 billion people sometime in the next hundred or so years. If this is the case, then it seems more reasonable that a one-time injection of additional resources, such as would be achieved by colonizing a few more planets, would get us over the hump.

But what about the resources it will take to get those colonies established? In the long run they may be self-sustaining, but big projects always take longer, cost more, and encounter more technical problems than you can forsee at the outset (even if your foresight takes this principle into account). In the comments to Marcotte's post, Clarke offers some stunning back-of-the-envelope calculations for the resources required just for moving a significant number of human bodies into near earth orbit -- never mind getting them to another planet and supplying them with the materials for survival and terraforming. So large-scale space colonization will actually increase the resource crunch on Earth. It's only a solution if you assume humans are extremely tenacious and extremely willing to remain committed to a grand collective goal at great expense to themselves for decades.

And of course all these arguments assume that we can move enough people off-planet fast enough. Given the expense and time taken to move even small crews of astronauts around, the idea of moving large populations of people seems unlikely within the time frame of the increase to 10 billion people.

I'm not opposed to space colonization as a long-term project and a defense against exogenous disasters like asteroids or the death of the sun. But I don't see it as a reasonable fix for any of the really pressing problems of the present.


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