Gee-Whiz Geoengineering

Just about two years ago, Chemistry Nobelist, and atmospheric scientist Paul Crutzen opened a huge can of worms by suggesting that, since the world doesn’t seem to be getting its act together to significantly reduce CO2 emissions, it would be prudent to think about emergency measures in which we engineer ourselves out of the crisis by monkeying directly with the Earth’s solar radiation input instead of dealing with the CO2 content of the atmosphere. The specific proposal was to inject chemicals into the stratosphere that would form sulfate aerosols and hence block sunlight. Crude estimates suggest that the aerosol fix (if it is indeed a fix and doesn’t create more problem than it solves) is more technologically feasible than sci-fi dreams of sunshades at the Lagrange point. Not to say technologically feasible, necessarily, but not so far out as the other schemes. Crutzen’s idea, and related geoengineering proposals, have been discussed here on RealClimate. The subject is once more in the news, thanks to this chipper little op-ed by Ken Caldeira, which appeared in the New York Times this week.

Update: I just noticed that our original RealClimate piece was done before Crutzen’s article was published. You’ll find his article here (subscription not required).

The attraction of the proposal is that we are already conducting an uncontrolled experiment on aerosol-based geoengineering, through the sulfate aerosols injected into the troposphere by dirty coal plants. Along with a lot of nasty health and environmental consequences, this has had some inadvertent benefits in restraining some aspects of global warming. As coal plants get cleaned up in the future some of the cooling aspect of the tropospheric aerosols will be lost. Since aerosols last much longer in the stratosphere than they do in the rainy troposphere, the amount of aerosol-forming substance that would need to be injected into the stratosphere annually is far less than what would be needed to give a similar cooling effect in the troposphere, though so far as the stratospheric aerosol burden goes, it would still be a bit like making the Earth a permanently volcanic planet (think of a Pinatubo or two a year, forever). It might make sense to take a small portion of the aerosol that would have been dumped into the troposphere by retired dirty coal plants, and inject that directly into the stratosphere where it will restore the lost cooling effect while (hopefully) doing less harm than the old stuff dumped into the lower atmosphere. To go farther, though, and count on offsetting the entire unrestrained CO2 production of the coming century with engineered aerosols is fraught with peril.

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