According to a new study published in Environmental Science Technology, hundreds of active hydropower plants are making a worse impact on the climate than fossil fuels.

Yup, you read that right: Hydropower, popularly seen as a green energy source — and a major clean energy source in a lot of emission-reduction plans — can release more greenhouse gases than coal- or oil-burning power plants, under certain conditions.

Scientists have known for a while now that hydropower facilities release greenhouse gases — mostly methane, but also CO2 and nitrous oxide. But the way they’ve historically calculated a facility’s climate impact has obscured methane’s heat-trapping potency. The new study, which looks at data from thousands of hydropower…