Recently, it was reported that a team of researchers from Switzerland's Ecole Polytechnique Federale de Lausanne has completed a wind tunnel study of the effect of large wind farms on local heat and humidity in the atmosphere. Unsurprisingly, the study, like others before it, found that the rotation of large wind turbines can change the distribution of heat and water vapor in the surrounding air, and speculated that this might affect the cultivation of crops near the turbines.
While this analysis is interesting from a theoretical point of view, its results should be kept in perspective.
First, any impact of wind on localized movements of air is likely to be extremely small. As one article noted, "the team found that the total change in surface heat flux produced by the wind farm was small – nearly zero for a wind farm with aligned turbines, and around 4% for a farm with a staggered layout."
Second, in many cases wind energy would actually provide a small but beneficial boost to crop growth. The study found that "the wind turbine cools the near-surface air in the summer, which helps crops to thrive," the article added. Previous analyses have also found that wind turbines could have a very small but beneficial impact on crop growth, including protecting many crops from frost during the winter: http://news.nationalgeographic.com/news/energy/2011/12/111219-wind-turbines-help-crops-on-farms/
Farmers and ranchers around the country are already reaping major benefits from wind energy, with many farmers and ranchers receiving thousands or tens of thousands of dollars in lease payments in exchange for using a few percent of their land for wind energy production. Because wind farms have a very small footprint, typically around 98% of the land can still be used for crops or ranching.
Third, given the very small impact observed in the study and the complexity of air movements in the atmosphere, one should be cautious about drawing significant conclusions from the study. The study was conducted in a 1/1000th scale wind tunnel that models wind flow from a single direction, which does not fully capture the three-dimensional complexity of how a wind project interacts with the atmosphere in real life.
It is also important to keep in perspective that nearly all human activities, such as planting crops, building cities, managing forests, and even operating nuclear power plants, can have localized impacts on movements of air, as demonstrated here: http://tinyurl.com/ar4efar . In fact, humans' far more widespread use of agriculture and irrigation have been known to affect weather patterns across large areas, and in some cases even alter the output of wind plants. http://green.blogs.nytimes.com/2010/09/09/the-irrigation-juggernaut/
Finally, readers should be careful not to draw erroneous conclusions from the paper’s analysis of how large deployments of wind turbines could slightly affect the mixing of air in the atmosphere. The paper makes it clear that any impact is very small, extremely localized, and short-lived. Readers should not confuse this simple effect of moving air around, which has no impact on the heat balance of the Earth, with the global warming that is caused by the introduction of long-lasting greenhouse gases that continually alter the Earth’s energy balance. Compared to the massive and global climate impact of burning fossil fuels, which wind energy use directly offsets, any small and localized weather impact of wind energy deployment is trivial. As documented by a recent comprehensive analysis of all peer-reviewed studies on the topic, wind and other forms of renewable energy are by far the lowest impact energy sources: http://www.nrel.gov/analysis/sustain_lca_results.html
Fact check: Harvard study misses real-world facts about wind power, February 27, 2013
Study's lead author: News reports on wind and temperature 'misleading', May 1, 2012
Fact check: Flawed science journalism on wind energy, April 30, 2012