Friday 16 November 2012

Do wind farms contribute to global warming?

Anaerobic Digestion News has just reported on a paper that appeared in Nature Climate Change some months ago (online in April, in print in July) describing evidence that wind farms cause increase in surface temperature. This was taken by some to mean that they contribute to global warming. Back in April/May there was a furore over this which AD News presumably missed.

These media stories say the research showed that wind farms cause climate change:

Wind farms can cause climate change in the Telegraph
New research shows wind farms cause global warming in Fox News

Others correctly understood that the increase in surface temperature reported was small and local and due only to changes in layering of air close to the ground.

Wind Farms Affect Local Weather in the BBC

No wind farms are not causing global warming (Washington Post)

The actual paper Impacts of Wind Farms on land surface temperatures states that '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.' I think the devil is in the 'per decade' bit. This seems to imply that the wind farms will continue to get warmer than the surrounding areas. What they actually meant is that the observations showed an increase in 0.7C in night time temperature between 2001-2003, before the wind farms were built, and 2009-2011 afterwards. The authors themselves seem to have been quite miffed by the misinterpretation of their article, according to the People's World: Do wind farms really cause global warming?

The night time temperature increase was predicted by atmospheric models. It is because at night time air close to the ground often cools while the warmer air above is more buoyant - the wind turbine blades produce turbulence which mixes these layers up, making the surface warmer. There was also a very slight increase in day time temperature, which the models had not predicted. The researchers say this is probably because the same turbulence from the turbine blades inhibits convection currents which would normally allow warm surface air to rise.

I am not sure if this change in temperature is useful in Texas but it could be very useful for fruit growers in regions prone to frost. Apparently orchard owners occasionally resort to blowing air fans or even driving helicopters over their trees to achieve a similar effect.

I do find it alarming that the wind farm global warming myth is still being propagated 7 months after it was debunked the first time and I don't understand why Anaerobic Digestion News is so small minded as to promote AD over all other forms of renewable energy. Personally I think we need all of them!

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