Methane plumes observed by Carbon Mapper during aerial surveys at a landfill in Georgia.
CNN  — 

Garbage piling up in landfills isn’t just an eyesore, it’s also a climate nightmare, belching out large amounts of planet-warming methane gas. In the United States, the problem could be much worse than previously thought, according to a new study measuring methane pollution at hundreds of landfills across the country.

Scientists flew over more than 200 landfills across 18 states from 2018 to 2022, in what they say is the largest measurement-based survey of America’s landfills. Their results revealed average methane emissions were much higher than those officially reported, according to the study published Thursday in the journal Science.

Methane — an invisible, odorless gas with over 80 times more warming power than carbon dioxide in the near-term — is produced by various sources, the biggest of which are oil and gas and agriculture. Landfills tend to be a less well-known methane source, but they also have a huge impact, estimated at around 20% of global human-caused methane emissions.