Do Wind Farms Really Cause Climate Change?
Posted April 30, 2012
A number of news outlets have picked up a recent paper that looks at the local land surface temperature impacts of large wind farms. This has resulted in a number of headlines like “Wind farms can cause climate change” and “Wind farms linked to temperature increase” (see additional stories here, here and here).
This wording is deeply misleading in this context and conflates small-scale, local impacts on nighttime land surface temperatures and global climate disruption. Using the same language to describe these two very different phenomena blatantly ignores the profound differences in magnitude, scope and severity that separate them. It’s like equating a bumblebee with Mothra.
If you read the text of these stories, you’ll discover that the paper’s findings don’t match the gravity implied by their silly headlines. For example, the telegraph story linked above says that “[the temperature changes are] much smaller than the estimated change caused by other factors such as man made global warming.”
Professor Sherwood from Cornell is quoted as saying “the wind farms generate gentle turbulence near the ground that causes these to mix together, thus the ground doesn't get quite as cool. This same strategy is commonly used by fruit growers (who fly helicopters over the orchards rather than windmills) to combat early morning frosts.”
Notice that this means that wind farms could actually extend growing seasons by reducing morning frost events. That would be a great ancillary benefit of siting turbine arrays on agricultural land and a welcome alternative to flying helicopters to accomplish the same end. It also gives you a sense of the scope and magnitude of this effect.
Both of these conclusions are supported by earlier research on this topic, which says:
"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."
"it may be comparatively easy to reduce the climatic impacts of wind turbines. Preliminary analysis suggests that turbine designs could be modified to increase the atmospheric efficiency (CP/CD) by several tens of percent and reduce the generation of turbulence by several fold, both of which could be done economically. Additional mitigation of impact might be achieved by siting wind farms such that their effects partially cancel and by tailoring the interaction of turbines with the local topography to minimize the added drag."
So what’s the bottom line?
Wind-induced turbulence does produce vertical mixing in the atmospheric boundary layer that increases nittime surface temperatures. This is a small, local impact that should not be confused with what is typically thought of as “climate change.” One possibe outcome of this local effect is that you would be able to extend growing seasons for crops grown near wind turbines. There might be additional impacts that haven’t yet been anticipated, but it is clear that these impacts bear no resemblance in scope, magnitude or severity to global climate disruption. Language matters. Unfortunately, some good media outlets have missed the ball on this one.
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