A cool if not quite cold wind is blowing over the ballyhooed environmental benefits of a big shift to wind power.
A group of Canadian and U.S. scientists reported Tuesday that computer simulations show that a large-scale use of wind farms to generate electrical power could create a significant temperature change over Earth's land masses.
While the precise tradeoff between the climate changes from wind farms versus that from carbon-based power systems is still a matter of contention, the fact that wind power isn't climate neutral leaps out of the simulations.
“We shouldn't be surprised that extracting wind energy on a global scale is going to have a noticeable effect. ... There is really no such thing as a free lunch,” said David Keith, a professor of energy and the environment at the University of Calgary and lead author of the report, which appeared in the Proceedings of the National Academy of Sciences.
Specifically, if wind generation were expanded to the point where it produced one-10th of today's energy, the models say cooling in the Arctic and a warming across the southern parts of North America should happen.
The exact mechanism for this is unclear, but the scientists believe it may have to do with the disruption of the flow of heat from the equator to the poles.
Depending on how much energy is ultimately generated by wind power, the study's simulations say these changes could range from one-third of a degree to 2 degrees Celsius.
One unexpected finding to the study is that the hotter temperate zone/cooler Arctic effect exists in the simulations if the wind farms are concentrated in a few spots or scattered across the world.
Prof. Keith and others involved in the study strongly caution, however, against an anti-wind-power reading of their work.
“This is really a ‘but, yes' article,” says Stephen Pacala, a professor of ecology at Princeton University, who is a co-author of the paper.
The “but” is the fact that wind farms would alter the climate, the “yes” is the paper's preliminary estimation that if wind power produced one-10th of today's energy, its climate-altering effects would be only one-fifth that of the carbon dioxide it would replace.
But there may also be a “yes, but” lying in the future.
Prof. Keith argues that the paper is so ringed with uncertainties that one cannot rule out scenarios where at some size wind farms might cause more climate ill than good.
Specifically, the new paper's simulations do not include any of the jaw-dropping calculations of the local temperature effects of large-scale wind farms that appeared last month.
Dr. Pacala's then-graduate student Somnath Roy and others reported that simulations of a wind farm in Oklahoma with 10,000 windmills could increase temperatures by upward of 2C for several hours in the early morning. These findings mirror an actual but previously ignored temperature rise that U.S. government meteorologist Neil Kelley observed at an actual wind farm in California in 1990.
The mechanism for local temperature changes are the vertical eddies that behemoth windmills – these monsters can be 30 stories tall and have turbines that spin at 400 kilometres an hour – would generate.
These local temperature shifts occurred because eddies heated, dried and lifted ground air.
Even before publication, the new paper has been intensely controversial.
Joseph Romm, a former acting assistant secretary of energy for the United States Department of Energy, wrote a blistering critique of early drafts in which he pointed out that carbon dioxide-induced global warming might cause a complete shift in the world's climate, whereas wind power would raise local temperatures only.
The scientists involved in the PNAS paper spent 1½years rewriting it.
“The first version of the paper caused a lot of outrage, and we are trying to pull our punches and not to draw conclusions,” Prof. Keith said.
Nonetheless, Dr. Keith says that after a rumour about his findings got out, he was contacted by a group fighting the establishment of a wind farm in Cape Cod in Massachusetts.
Wind power's proponents are cautiously optimistic that all climate changes will prove minor when compared with the sea level rises, crop failures, and disease spread that have been linked to the continuing use of carbon based energy sources.
“It seems to me this is an area that requires further research to see if there is a problem there ... although there doesn't seem to be anything in the paper itself that leads you to that conclusion,” says Robert Hornung, president of the Canadian Wind Energy Association.