In 2010, Somnath Baidya Roy, an associate prof in the Atmospheric Sciences department at the University of Illinois, wrote a paper on wind farms and microclimatology. The key here is micro; the implications of it were modest in scope, at least in terms of physical scope:
Although debates exist regarding the global-scale effects of wind farms, modeling studies agree that wind farms can significantly affect local-scale meteorology. However, these studies are based only on model simulations and are not validated against observational evidence.
Very little such observational evidence exists in the public domain. Looking at data taken from a California wind farm in 1989, Roy found that it did have an effect on its microclimate:
Data from the field campaign show that near-surface air temperatures downwind of the wind farm are higher than upwind regions during night and early morning hours, whereas the reverse holds true for the rest of the day Thus, this wind farm has a warming effect during the night and a cooling effect during the day.
A possible explanation for this phenomenon can be drawn from the hypothesis proposed by Baidya Roy et al. that turbulence generated in the wake of the rotors enhance vertical mixing. In a stable atmosphere when the lapse rate is positive, i.e., a warm layer overlies a cool layer, enhanced vertical mixing mixes warm air down and cold air up, leading to a warming near the surface. In an unstable atmosphere with negative lapse rate, i.e., cool air lying over warmer air, turbulent wakes mix cool air down and warm air up, producing a cooling near the surface.
Simple enough. Then it got sucked into the climate-change noise machine, and it got a lot less simple. The Daily Mail ran with the sensational headline "Wind farms can actually INCREASE climate change by raising temperatures and causing downpours, warn academics." The story was a bit more reasonable, though you can see the story start to mutate:
The study found that currently the effect is restricted to areas near to the turbines, but the increase in larger farms could create weather changes on a regional scale.
Many of these wind farms are coming up over agricultural land, helping farmers supplement their income with rent from utility companies. Impacts from wind farms on surface meteorological conditions are likely to affect agricultural practices in these farms. In some cases, these impacts may prove to be beneficial, such as the nocturnal warming under stable conditions can protect crops from frosts. If the wind farms are sufficiently large, they may also affect downstream surface meteorology (3).
But that's not Roy's conclusion; it's a reference to a 2008 paper, "On the Climate Impact of Surface Roughness Anomalies" (PDF), which asks the question:
In addition, other human activities (deforestation, urbanization) and natural phenomena (climate shifts) have resulted in large changes in surface roughness characteristics, and so the question of how a regional change in surface roughness might influence atmospheric circulation patterns is of some general interest.
Steve Tracton, of the Washington Post's excellent weather blog, addressed the paper:
"If you have a couple of wind farms over a 10-kilometer patch in the Midwest, that's not going to make some kind of global impact on the weather," said University of Maryland atmospheric scientist Daniel Kirk-Davidoff in a recent Christian Science Monitor story. But if the whole Midwest "is somewhat roughened over a large area, then you could imagine having a large-scale impact on the atmosphere."
What remains unclear is how the impact of wind farms might compare to, for example, the effects of high-rise complexes or, for that matter, the influence of building a whole new city dominated by skyscrapers, such as that occurring at several locations across China. And yes, disturbances of the atmosphere originating in China can and frequently do impact weather systems affecting the United States in the matter of just a few days (to be discussed in a later post).
Basically: you change wind patterns, you change the weather, whether it's from building skyscrapers, cutting down trees, or building wind farms. How and how much is the question, and it's a very difficult one. After the paper pingponged back and forth across the pond, Leo Hickman of the Guardian did some wonderful media-detective work, tracing the path from Roy's paper through the madness of climate-change coverage, eventually speaking to a frustrated Roy. Of course, by that time, many people had heard what they wanted to hear:
More windmills to fight global warming = more global warming. You have to love it.
Of course, for this to be really meaningful first you have to believe global warming is harmful. Then you have to believe it’s happening in a huge way. Then you have to believe that man’s paltry efforts have anything to do with it.
So we shouldn't build wind farms, because of the effects they don't have on the thing that's not a problem.
Wind farms are sprouting slowly in the Midwest—one of the more eerie sights around these parts is the giant turbines along I-65 in Indiana, soporifically rotating during the day and ominously flashing their aerial warning lights in sync at night. (That's why I think Indiana drivers are so prone to, say, hanging out in the passing lane for miles at a time: they're hypnotized. Unfortunately, there's nothing in Roy's paper addressing this phenomenon.) And climatological effects aren't the only concern:
How you feel about setbacks will depend on how you feel about the tales of woe spread by people like Lynda Barry on her Web site, Better Plan, Wisconsin (betterplan.squarespace.com). She insists the low-frequency rumble of the turbines, more felt than heard, and the flickering sunlight thrown by the spinning blades cause people living nearby to suffer from nausea, incessant headaches, and insomnia. Barry e-mailed Scott Milfred, editor of the Journal’s editorial page, and told him the paper’s jeering cartoon simply added to the victims’ “hopelessness of ever having their story told.”
These implications bear study; one of the lessons of climate change should be the unintended consequences of promising large-scale energy generation. But these studies work slowly, much more slowly than the news cycle.
Photograph: juggernautco (CC by 2.0)