Monday, June 12, 2006

Space Mirrors: AEI's solution to climate change

[updates below]

Yes, Steven Hayward of the American Enterprise Institute now appears to be willing to admit that climate change is a going concern.

But rather than tackle the intertwined problems of energy consumption, energy supply, global conflicts, and a fast-growing developing world, Steven Hayward offers this solution (and I'm not kidding):
... we should consider climate modification. If humanity is powerful enough to disrupt the climate negatively, we might also be able to change it for the better. On a theoretical level, doing so is relatively simple: we need to reduce the earth’s absorption of solar radiation. A few scientists have suggested we could accomplish this by using orbiting mirrors to rebalance the amounts of solar radiation different parts of the earth receive. Right now this idea sounds as fanciful as Ronald Reagan’s Strategic Defense Initiative seemed in 1983, but look what that led to. New York University physicist Martin Hoffert points out that the interval between the Wright brothers’ first flight at Kitty Hawk and Neil Armstrong’s first step on the moon was a mere sixty-six years. It is entirely reasonable to expect vast changes in our technical capacity before the century is out.
OH ... MY ... GOD.

Let's see, to reduce insolent radiation by, say, 10%, would require that something on the order of 5-10% of the equatorial land area between 30 S and 30 N be covered by mirrors

... from space.

To minimize penumbras -- those half-shadows that surround the full shadows cast by objects due to the very large size of the Sun -- the mirrors would have to be solid sheets stretching over enormous areas. And at an orbital altitude of at least 400 miles, this massive, unbroken mirror would require an area of at least 6 million square miles (assuming a 3936 mile Earth radius, and 5% coverage of the area between 30 S and 30 N).

Light weight reflective mylar weighs about 50 tons per square mile. Forgetting for the moment that the Space Shuttle's maximum payload weight is only 25 tons, an effective mirror would require over 300 million tons of mylar, and therefore about 10 million space shuttle launches.

And don't forget space junk. The only reason the shuttle doesn't get hit is because it's small. A 6 million square mile mirror is another story.

Finally, Ronald Reagan's SDI? Please.

Hayward's piece just goes to show: AEI folks have no sense of scale.

UPDATE: I made a serious boo-boo. I calculated area as 4 pi R^3, rather than 4 pi R^2. All corrections are reflected above. Thanks to phillies at DailyKos for catching the math error. I used to work on global carbon cycling models and was familiar with things like the surface area of the Earth, but that was ten years ago -- yet, I knew something didn't add up.

The mylar would cost about $5 trillion dollars, assuming a 90% volume discount on 12 micron PET from commercial sources such as McMaster-Carr, and that's just to buy the film -- never mind the structural supports.

Ten million launches would use a lot of fuel. If each launch consumes the equivalent of 2 minutes worth of gas at current US gasoline consumption rates (equivalent to 445,000 gallons of gas), then 10 million launches would consume about 380 years worth of gas at current US gasoline consumption. This would cost global taxpayers on the order of $11 trillion at $2.50 a gallon.

So far, then, my conservative estimate suggests that production and deployment of the space mirrors would more than double our national debt.

And I thought the AEI was supposed to be fiscally conservative. So much for their stand against government entitlements.

UPDATE II (11:00 AM, 6/13/2006): Steven Hayward has contacted me with his source for the Space Mirror program. He is right to make clear to me that it was not his idea, but that it instead originated in an article in the journal Science. The article, entitled "Advancing technology paths to global climate change stability: energy for a greenhouse planet," was published in 2003 (Science 298: 981-987) with Martin I. Hoffert at NYU's Department of Physics as the lead author.

Hoffert et al.'s conception of the space mirrors is different from what I had conceived:
Perhaps most ambitious is a proposed 2000-km-diameter mirror of 10-micron glass fabricated from lunar materials at the L1 Lagrange point of the Sun-Earth system [i.e., stationary between the Earth and Sun, at about 1 million miles from the Earth and thus 4 times the distance between the Earth and Moon]. The mirror’s surface would look like a permanent sunspot, would deflect 2% of solar flux, and would roughly compensate for the radiative forcing of a CO2 doubling. Climate model runs indicate that the spatial pattern of climate would resemble that without fossil fuel CO2.
In an accompanying figure, the mirror is shown as a Fresnel mirror, which would diffract, not reflect, incoming solar radiation. Hoffert et al. go on [emphasis mine]:
It is only prudent to pursue geoengineering research as an insurance policy should global warming impacts prove worse than anticipated and other measures fail or prove too costly. Of course, large-scale geophysical interventions are inherently risky and need to be approached with caution.
In the interest of fairness to Hayward, let me just say that Hoffert et al.'s concept is looney. A 3 million square kilometer Fresnel mirror (i.e., carefully etched glass) would still require manned space flights until kingdom-come. I don't feel it's necessary for me to do the calculations needed to give a cost estimate (Hayward, or perhaps an enterprising National Review reader, should do it), but shame on Hoffert et al. for not even considering, let alone comparing, potential costs. If a Fresnel mirror at the L1 Lagrange point costs anything like the mirror I envisioned above, it would be far more cost effective to cut our fossil fuel consumption, or plant a trillion trees. We need to get over our all-to-eager embrace of "Star Trek" technology.

On the other hand, technological advances, like some of those proposed by Hoffert et al., are exactly what could make a new "green revolution" economically attractive for both business and labor. People at the ApolloAlliance are leading the way (hopefully), but they're keeping it simple. And their suggestions don't require a permanent base on the Moon.

(Image source NASA)

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