A Harvard University study suggests that, under certain conditions and in the near term, increased wind power could mean more climate warming than would be caused by the use of fossil fuels to generate electricity. The study found that if wind power supplied all U.S. electricity demands, it would warm the surface of the continental United States by 0.24 ˚C, which could significantly exceed the reduction in U.S. warming achieved by decarbonizing the nation’s electricity sector this century—around 0.1 ˚C. The warming effect depends strongly on local weather conditions, as well as the type and placement of the wind turbines.
According to the Harvard researchers, the findings closely matched directly observed effects from hundreds of U.S. wind farms. In the Harvard scenario, the warming effect from wind was 10 times greater than the climate effect from solar farms, which can also have a warming effect. The Harvard University researchers also concluded that the transition to wind or solar power in the United States would require 5 to 20 times more land than previously thought.
The Research Approach
To estimate the impacts of wind power, the researchers established a baseline for the 2012 to 2014 U.S. climate using a standard weather-forecasting model. They covered one-third of the continental United States with enough wind turbines to meet present-day U.S. electricity demand. The researchers found this scenario would warm the surface temperature of the continental United States by 0.24 degrees Celsius, with the largest changes occurring at night when surface temperatures increased by up to 1.5 degrees. This warming is the result of wind turbines actively mixing the atmosphere near the ground and aloft while simultaneously extracting from the atmosphere’s motion.
The Harvard researchers found that the warming effect of wind turbines in the continental U.S. would be larger than the effect of reduced emissions for the first century of its operation. This is because the warming effect is predominantly local to the wind farm, while greenhouse gas concentrations must be reduced globally before the benefits are realized. The direct climate impacts of wind power are instant, while the benefits of reduced emissions accumulate slowly.
According to one of the researchers, “If your perspective is the next 10 years, wind power actually has—in some respects—more climate impact than coal or gas. If your perspective is the next thousand years, then wind power has enormously less climatic impact than coal or gas.”
The U.S. Geological Survey provided the researchers with the locations of 57,636 wind turbines around the United States. Using this data and several other U.S. government databases, they were able to quantify the power density of 411 wind farms and 1,150 solar photovoltaic plants operating in the United States during 2016. For wind, the average power density—the rate of energy generation divided by the encompassing area of the wind plant—was up to 100 times lower than estimates by some energy experts because most of the latter estimates failed to consider the turbine-atmosphere interaction. For an isolated wind turbine, the interactions do not matter. For wind farms that are more than 5 to 10 kilometers deep, the interactions have a major impact on the power density.
For solar energy, the average power density (measured in watts per meter squared) is 10 times higher than wind power, but also much lower than estimates by leading energy experts, including the U.S. Department of Energy and the Intergovernmental Panel on Climate Change.
Clearly, the scenario developed by the Harvard researchers is unlikely to occur, i.e., the United States is unlikely to generate as much wind power as the researchers simulate in their scenario. Despite that, the researchers found that localized warming occurs in even smaller wind generation projections. Thus, the warming phenomena of wind farms is a factor that politicians, utility planners, and the public should consider when determining which technologies should be built and what subsidies should be enacted or extended.