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Can Giant Space Sunshades Save Us?

Are we doomed already? It’s hard not to get that impression reading Brad’s post on the recent NOAA study suggesting that even the level of carbon dioxide currently present in the earth’s atmosphere is enough to cause droughts, melting ice caps, and ocean acidification for, oh, the next 1,000 years. Going past today’s carbon-dioxide concentrations—even if we manage to stop at the challenging but oft-cited limit of 450 parts per million—will make these problems even worse.  So even if the world gets its collective act together, a lot of distressing climate trends are not going to reverse themselves. But might it be possible to stage a series of active interventions aimed at putting the climate system back in order? That’s the question posed by a new study in the journal Atmospheric Chemistry and Physics that attempts to list and quantify the potential effectiveness of all the various geoengineering schemes that climate scientists have been throwing around.

It’s a list that contains some imaginative ideas—like launching giant sunshades into space—but, unfortunately, most of these ideas carry pretty serious costs, financial or otherwise. The authors note, for example, that even if there already were enough sunshades in space to counteract the radiative forcing caused by current levels of carbon-dioxide, it would take another 31,000 square kilometers of sunshades each year (which, as they helpfully calculate, would require some 135,000 annual rocket launches for deployment) to make up for the CO2 that we’re adding to the atmosphere.

So sunshades are probably out, even though the study does find that they’d be the single most effective form of geoengineering. The next most effective measure—seeding the stratosphere with reflective aerosols—could have some serious side-effects, like widespread drought. From there on down, the various geoengineering measures—like increasing the reflectivity of the earth’s deserts, or removing carbon-dioxide from the atmosphere using biofuel power plants with carbon sequestration—would have to be combined with each other to make a serious difference. Interestingly, the study finds that schemes for increasing the carbon uptake of the oceans—by fertilizing them with iron or calcium carbonate or by increasing downwelling or upwelling—would have some of the smallest impacts of all.

So it doesn’t sound like the geoengineers are going to be single-handedly saving the planet. But some of their ideas certainly have merit, especially the ones for removing carbon dioxide from the atmosphere. Biochar, anyone?

--Rob Inglis