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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.

It is reported China is now erecting 36 wind turbines every day and Texas is the largest producer of wind power in the US.

Liming Zhou, Research Associate Professor at the Department of Atmospheric and Environmental Sciences at the University of New York, who led the study, said further research is needed into the affect of the new technology on the wider environment.

"Wind energy is among the world’s fastest growing sources of energy. The US wind industry has experienced a remarkably rapid expansion of capacity in recent years,” he said. “While converting wind’s kinetic energy into electricity, wind turbines modify surface-atmosphere exchanges and transfer of energy, momentum, mass and moisture within the atmosphere. These changes, if spatially large enough, might have noticeable impacts on local to regional weather and climate.”

The study, published in Nature, found a “significant warming trend” of up to 0.72C (1.37F) per decade, particularly at night-time, over wind farms relative to near-by non-wind-farm regions.

The team studied satellite data showing land surface temperature in west-central Texas.

“The spatial pattern of the warming resembles the geographic distribution of wind turbines and the year-to-year land surface temperature over wind farms shows a persistent upward trend from 2003 to 2011, consistent with the increasing number of operational wind turbines with time,” said Prof Zhou.

However Prof Zhou pointed out the most extreme changes were just at night and the overall changes may be smaller.

Also, it is much smaller than the estimated change caused by other factors such as man made global warming.

“Overall, the warming effect reported in this study is local and is small compared to the strong background year-to-year land surface temperature changes,” he added.

The study read: "Despite debates regarding the possible impacts of wind farms on regional to global scale weather and climate, modelling studies agree that they can significantly affect local scale meteorology."

Professor Steven Sherwood, co-Director of the Climate Change Research Centre at the University of New South Wales, said the research was ‘pretty solid’.

“This makes sense, since at night the ground becomes much cooler than the air just a few hundred meters above the surface, and 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.”
 

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