There's a new enemy in the battle against global warming: reservoirs. Researchers studying more than 250 of the world's reservoirs found they produce the equivalent of 1 gigaton of carbon dioxide every year, the Washington Post reports. According to Popular Science, that's about the same amount of greenhouse gas as Brazil produces annually and includes 25% more methane than previously believed. About 79% of the greenhouse gases emitted by reservoirs is methane (the rest is carbon dioxide and nitrous oxide). That's not great news as methane is about 34 times more potent than carbon dioxide when it comes to exacerbating global warming, Phys.org reports.
Reservoirs produce more greenhouse gases than natural bodies of water because they include more organic matter in the water—the grasses and trees that were flooded, runoff from nearby farms—for microorganisms to break down. Unfortunately, more and more reservoirs are being built, especially in developing countries and as a way to meet climate change goals, the Christian Science Monitor reports. So it now appears hydropower, which uses reservoirs, may not be as green as previously believed. Researchers say it's time the world starts paying attention to reservoirs. They produce about as much methane as rice paddies and biomass burning but aren't included in international emissions estimates like those other two. (California is going after its farting cows.)