January 29, 2009

Atmospheric Hacking

By: Daniel Kennelly

Wired has an interesting write-up of a study comparing the potential of various “climate hacks”–that is, geoengineering schemes for dealing with climate change. These “hacks” essentially fall into two categories: 1) decreasing the amount of short-wave radiation from the sun that goes through our atmosphere and hits the surface, and 2) increasing the amount of long-wave radiation that’s reflected out into space. (Carbon dioxide lowers the amount of long-wave radiation reflected back into space, hence the whole warming thing.)

The study estimates that current CO2 levels mean the Earth is retaining 1.6 watts/m² more than it did in 1800, and that a doubling of current CO2 levels would mean the Earth would retain 3.7 watts/m² more than it did in 1800. So these two figures offer convenient guideposts for determining what kind of cooling effect geoengineering plans could produce in a best-case scenario.

The good news is that there are two methods that, all on their own, could at least conceivably counteract carbon-dioxide-caused radiative forcing in terms of the two W/m² guideposts mentioned above: 1) injection of aerosols into the upper atmosphere, whether sulphur dioxide or some alternative substance, and 2) increasing marine stratiform cloud albedo by means of mechanically generated sea salt spray, or some other means of artificially increasing the levels of cloud condensation nuclei. The bad news is that this study doesn’t really look at the environmental effects of these methods, which in the case of stratospheric aerosols could be pretty bad indeed, depending on the materials used and how they’re delivered.

The lessons for those of us who have little time or inclination to understand what the lab coat guys are saying? First, we need some sort of framework for evaluating geoengineering proposals. Studies like the above give us a starting point but are far from definitive. And second, there are probably no policy silver bullets when it comes to this issue. It’s likely that some combination of mitigation of carbon-dioxide emissions and geoengineering plans will give us the best way forward.