To extract energy, all renewables must alter natural energy fluxes, so climate impacts are unavoidable, but the magnitude and character of climate impact varies widely. Wind turbines generate electricity by extracting kinetic energy, which slows winds and modifies the exchange of heat, moisture, and momentum between the surface and the atmosphere. Observations show that wind turbines alter local climate and models show local- to global-scale climate changes from the large-scale extraction of wind power. Previous studies have assessed climate impacts of hydropower,16 biofuels,17 and solar photovoltaic systems (PVs).18 Rapid expansion of renewable energy generation is a cornerstone of efforts to limit climate change by decarbonizing the world’s energy system. In addition to climate benefits, wind and solar power also reduce emissions of criteria pollutants (NOx, SOx, and PM2.5) and toxic pollutants such as mercury that cause significant public health impacts.19, 20 The climate impacts of wind and solar are small compared with the impacts of the fossil fuels they displace, but they are not necessarily negligible. Improved understanding of the environmental trade-offs between renewables would inform choices between low-carbon energy sources. With growth of wind and solar PVs far outstripping other renewables,21 we combine direct observations of onshore wind power’s impacts with a continental-scale model, and compare it to prior estimates of PVs’ impacts to assess the relative climate impacts of wind and solar energy per unit energy generation.
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