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 21^st century warming, but large compared to the effect of reducing US electricity emissions to zero with solar.

In the journal Joule, Harvard researchers report the most accurate modelling yet of how increasing wind power would affect climate. They find that large-scale wind power generation would warm the Continental United States 0.24 degrees Celsius because wind turbines redistribute heat in the atmosphere.

Source: Miller and Keith (2018a)

Wind beats coal by any environmental measure, but that doesn’t mean that its impacts are negligible. We must quickly transition away from fossil fuels to stop carbon emissions. In doing so, we must make choices between various low-carbon technologies, all of which have some social and environmental impacts.

—senior author David Keith, an engineering and public policy professor at Harvard

Wind turbines generate electricity but also alter the atmospheric flow, explained first author Lee Miller. These effects redistribute heat and moisture in the atmosphere, impacting climate. The researchers attempted to model these effects on a continental scale.

To compare the impacts of wind and solar, Keith and Miller 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 decarbonizing the energy system in the latter half of this century. This scenario would warm the surface temperature of the Continental US by 0.24 degrees Celsius.

Their analysis focused on the comparison of climate impacts and benefits. They 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. 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.

—David Keith

More than ten previous studies have 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. They found that, for the same energy generation rate, solar power’s impacts would be about 10 times smaller than wind. But both sources of energy have their pros and cons.

In terms of temperature difference per unit of energy generation, solar power has about 10 times less impact than wind. But there are other considerations. For example, solar farms are dense, whereas the land between wind turbines can be co-utilized for agriculture.

—Lee Miller

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.

The work should not be seen as a fundamental critique of wind power. Some of wind’s climate impacts may be beneficial. So 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 decarbonizing the energy system.

—David Keith

Keith and Miller also have a related paper being published in Environmental Research Letters which validates the generation rates per unit area simulated in the Joule paper using observations.

This research was funded by the Fund for Innovative Climate and Energy Research. David Keith is a board member and acting chief scientist at Carbon Engineering, a clean energy company that aims to make carbon-neutral transportation fuels from wind and solar power.

Resources

• Miller and Keith (2018a) “Climatic Impacts of Wind Power,” Joule doi: 10.1016/j.joule.2018.09.009

• Miller and Keith (2018b) “Observation-based solar and wind power capacity factors and power densities” Environ. Res. Lett. 13 doi: 10.1088/1748-9326/aae102