Hot air about wind farms
A paper by Liming Zhou and friends appeared in Nature Climate Change on April 29, 2012:
The wind industry in the United States has experienced a remarkably rapid expansion of capacity in recent years and this fast growth is expected to continue in the future. While converting wind’s kinetic energy into electricity, wind turbines modify surface–atmosphere exchanges and the transfer of energy, momentum, mass and moisture within the atmosphere. These changes, if spatially large enough, may have noticeable impacts on local to regional weather and climate. Here we present observational evidence for such impacts based on analyses of satellite data for the period of 2003–2011 over a region in west-central Texas, where four of the world’s largest wind farms are located. Our results show a significant warming trend of up to 0.72 °C per decade, particularly at night-time, over wind farms relative to nearby non-wind-farm regions. We attribute this warming primarily to wind farms as its spatial pattern and magnitude couples very well with the geographic distribution of wind turbines.
The effect is clearly local and due to mixing of different layers of air over the same point as the ground. As a result, at the ground level the temperature rises by less than a tenth of a degree per year. No extra heat is added to the atmosphere, so this does not contribute to global climate change. The overall effect of this mixing is still unclear.
WSJ seemed to have the most balanced article among the hundreds now out:
Large wind farms slightly increase temperatures near the ground as the turbines’ rotor blades pull down warm air, according to researchers who analyzed nine years of satellite readings around four of the world’s biggest wind farms.
The study showed for the first time that wind farms of a certain scale, while producing clean, renewable energy, do have some long-term effect on the immediate environment.
Using sensors aboard a NASA satellite, researchers at the University at Albany-State University of New York, and the University of Illinois systematically tracked a cluster of wind farms in central Texas as the installations grew from a few dozen turbines in 2003 to more than 2,350 by 2011.
Despite long-standing interest in the environmental impacts of such large-scale alternative-energy installations, this is the first time anyone has measured how wind turbines can alter local temperatures over the long term, the scientists said. So far, the scientists don’t know if these higher temperatures affect local rainfall or other weather patterns.
Normally, the nighttime air is a layer cake of cool and warm air, caused as hot air rises and cold air sinks, with the coolest air closest to the ground. As the giant rotor blades churn the air, they draw the warmer nighttime air down to the surface.
“If you have a wind turbine spinning, there is a lot of turbulence in the wake just like a boat in the water,” said Mr. Roy. “The turbine pulls warm air from aloft and pulls it down and takes cooler air underneath and pushes it up. That creates a warming effect near the surface.”
Although the researchers detected some daytime warming because of the wind farms, the temperature changes were highest in the predawn hours, when the air normally is still and not so turbulent, the researchers said.
Speculation took over everyone else. The UK Telegraph couldn’t help spicing up an otherwise responsible article with a dash of disaster:
Usually at night the air closer to the ground becomes colder when the sun goes down and the earth cools.
But on huge wind farms the motion of the turbines mixes the air higher in the atmosphere that is warmer, pushing up the overall temperature.
Satellite data over a large area in Texas, that is now covered by four of the world’s largest wind farms, found that over a decade the local temperature went up by almost 1C as more turbines are built.
This could have long term effects on wildlife living in the immediate areas of larger wind farms.
It could also affect regional weather patterns as warmer areas affect the formation of cloud and even wind speeds.
The Guardian was super careful; preferring to quote experts:
“The result looks pretty solid to me,” said Steven Sherwood at the climate change research centre at the University of New South Wales, Australia. “The same strategy is commonly used by fruit growers, who fly helicopters over the orchards rather than erect windmills, to combat early morning frosts.”
“Overall, the warming effect reported in our study is local and is small compared to the strong year-to-year changes” that result from natural variation, said Zhou. The study is published in the journal Nature Climate Change.
He told the Guardian that his results could not be used as an justification for blocking new windfarms. “The warming might have positive effects,” he said. “Furthermore, this study is focused only on one region and for only 9 years. Much more work is needed before we can draw any conclusion.”