Three-Toed Sloth

Sow the Wind, Reap the Drag Coefficient (Dept. of "We are as gods, and might as well get good at it")

I wrote this about a year ago; I'm cleaning out my drafts folder.

As a paid-up member of the Viridian movement, I it would be a Very Good Thing for industrial civilization to find a power source which will let it run and grow without choking on its own waste. (I'm no good at ranting about this, so if you're curious I refer you to the master.) But it would be foolish to pretend that non-fossil-fuel power sources will not carry their own costs, including the possibility to alter the climate, and something worse than foolish not to consider those costs. After all, one of the Viridian design principles advises us to "Look at the Underside First":

Legions of people are paid large sums to promote the positive aspects of commercially available products. Very few people earn their daily bread by pointing out malfunctions, bugs, screw-ups, design failures, side-effects and the whole sad galaxy of trade-offs and failings that are inherent in any technological artifact. To counteract this gross social imbalance, a wise designer and a wise critic will make it a matter of principle to look at the underside first.

In which spirit, I bring you the following.

David W. Keith, Joseph F. DeCarolis, David C. Denkenberger, Donald H. Lenschow, Sergey L. Malyshev, Stephen Pacala and Philip J. Rasch, "The influence of large-scale wind power on global climate", Proceedings of the National Academy of Sciences (USA) 101 (2004): 16115--16120 [free via open access]

Abstract: Large-scale use of wind power can alter local and global climate by extracting kinetic energy and altering turbulent transport in the atmospheric boundary layer. We report climate-model simulations that address the possible climatic impacts of wind power at regional to global scales by using two general circulation models and several parameterizations of the interaction of wind turbines with the boundary layer. We find that very large amounts of wind power can produce nonnegligible climatic change at continental scales. Although large-scale effects are observed, wind power has a negligible effect on global-mean surface temperature, and it would deliver enormous global benefits by reducing emissions of CO2 and air pollutants. Our results may enable a comparison between the climate impacts due to wind power and the reduction in climatic impacts achieved by the substitution of wind for fossil fuels.

There are basically three channels through which wind power would influence climate. The first is direct increase of friction in the vicinity of the turbine, which dissipates kinetic energy in the wind into heat. The second is that the increased drag produced by the turbines will change the speed and direction of prevailing winds, and since these winds carry heat and moisture, can potentially alter the climate over large areas. The third, and most indirect, channel is that increasing use of wind power may reduce the amount of fossil fuel consumption, and interact with climate changes produced by the existing load of greenhouse gases.

The present paper is a first cut at considering all three channels, using two standard global climate models and a variety of different assumptions about where wind-turbines will be situated, how efficient they will be, and the manner and magnitude of the resulting increase in surface-layer drag. There are plenty of crude approximations made here (for instance, that the increase in drag is uniform over the affected area), but they're recognized as such. The results thus need to be treated with caution, but they are interesting. The second channel (changing atmospheric transport) has a much bigger impact than the first (direct friction); together, under plausible assumptions, they give a near-zero impact on the global mean, root-mean-square change in seasonal means of about one twentieth of a degree centigrade at one point, and peak changes of half a degree. Under further plausible, but of course more arguable, assumptions, the third channel (reduced carbon emissions) swamps these effects, too, by about a factor of five. Interestingly, the configurations for wind power they consider tend to cool the poles and warm the lower lattitudes, while carbon dioxide warming has the opposite effect. This suggests (though the authors don't go there) that we might consider massive wind farms as a pure climate-change moderator, even if they weren't a practical power source from an engineering point of view.

It should probably be noted that the first two sponsors listed in the acknowledgments are British Petroleum and the Electric Power Research Institute.

The Great Transformation