Large-scale wind power would cause warming in the US

Harvard University researchers have reported what is claimed to be the most accurate modelling yet of how increasing wind power would affect climate. Published in the journal Joule, their work finds that large-scale wind power generation would warm the Continental United States 0.24°C because wind turbines redistribute heat in the atmosphere.

All large-scale energy systems have environmental impacts, and the ability to compare the impacts of renewable energy sources is an important step in planning a future without coal or gas power. Extracting energy from the wind causes climatic impacts that are small compared to current projections of 21st-century warming, but large compared to the effect of reducing US electricity emissions to zero with solar.

“Wind turbines generate electricity but also alter the atmospheric flow,” said Lee Miller, first author on the study. “Those effects redistribute heat and moisture in the atmosphere, which impacts climate. We attempted to model these effects on a continental scale.”

To compare the impacts of wind and solar, Miller and senior author David Keith started by establishing a baseline for the 2012–2014 US climate using a standard weather forecasting model. Then they added in the effect on the atmosphere of covering one-third of the Continental US with enough wind turbines to meet present-day US electricity demand. This is a relevant scenario if wind power plays a major role in decarbonising the energy system in the latter half of this century — and was found to warm the surface temperature of the Continental US by 0.24°C.

“Wind beats coal by any environmental measure, but that doesn’t mean that its impacts are negligible,” said Keith.

Focusing on the comparison of climate impacts and benefits, the researchers found that it would take about a century to offset that effect with wind-related reductions in greenhouse gas concentrations. This timescale was roughly independent of the specific choice of total wind power generation in their scenarios.

“The direct climate impacts of wind power are instant, while the benefits accumulate slowly,” said Keith. “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 is enormously cleaner than coal or gas.”

With more than 10 previous studies having now observed local warming caused by US wind farms, Keith and Miller compared their simulated warming to observations and found rough consistency between the observations and model. They also compared wind power’s impacts with previous projections of solar power’s influence on the climate — and found that, for the same energy generation rate, solar power’s impacts would be about 10 times smaller than wind.

“In terms of temperature difference per unit of energy generation, solar power has about 10 times less impact than wind,” said Miller. “But there are other considerations. For example, solar farms are dense, whereas the land between wind turbines can be co-utilised for agriculture.” The density of wind turbines and the time of day during which they operate can also influence the climatic impacts.

Keith and Miller’s simulations do not consider any impacts on global-scale meteorology, so it remains somewhat uncertain how such a deployment of wind power may affect the climate in other countries. According to Keith, “The work should not be seen as a fundamental critique of wind power … rather, the work should be seen as a first step in getting more serious about assessing these impacts.

“Our hope is that our study, combined with the recent direct observations, marks a turning point where wind power’s climatic impacts begin to receive serious consideration in strategic decisions about decarbonising the energy system.”