Nearly 20 US states have started to implement former president Barack Obama’s Clean Power Plan, which places limits on carbon dioxide emissions from power plants in an effort to reduce the impacts of climate change. The plan has been in legal limbo for the past year, yet scientists have now calculated another outcome of the policy: harm to crop yields if the plan is stopped. Along with carbon pollution, coal-fired power plants spew pollutants that form smog, which was already known to contribute to increased rates of asthma and premature deaths. The new research estimates the extent to which smog, under air-pollution policies in place before the Clean Power Plan, would limit production in 2020 of four major crops: corn, cotton, potatoes, and soybeans. Led by environmental engineer Shannon Capps, the research team also estimated the extent to which those crop production losses would shrink under three nationwide counter scenarios. One improved the efficiency of individual power plants. Another modelled a policy similar to the Obama plan, setting state carbon dioxide emission goals for the electricity sector. And the third established a tax on carbon emissions, under which emissions decreased the most. But the greatest drop in smog-forming pollutants – and the greatest gains in crop yields – came from policies such as the Clean Power Plan.