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Methane spewing from major US landfills is on average 40% greater than reported, according to a new study published in Science in which scientists used aerial surveys to identify point source emissions from hundreds of waste sites.
The analysis suggests that while the emissions are significantly under reported they also present a major opportunity for mitigation because many of the releases persist for months or even years. Airborne observations offer important advantages over current survey approaches that typically involve a worker walking across portions of the landfill with a detector logging locations of high surface concentrations of methane.
The potent and invisible greenhouse gas, which has more than 80 times the warming capacity of carbon dioxide during its first 20 years in the atmosphere, is the primary component of fossil gas but it’s also generated from piles of garbage when organic materials like food scraps break down in the absence of oxygen. Satellites have also helped identify dumps, landfills and waste sites from India to Argentina as methane hotspots.
Scientists in the latest report observed more than 200 active landfills in 18 states that participate in the US Environmental Protection Agency’s Greenhouse Gas Reporting Program. They found that 52% of the surveyed sites had observable point source emissions — meaning it was clear to see they were a direct source of methane.
Methane from landfills make up roughly 20% of global emissions of the gas and are the third biggest source after agriculture and fossil fuels attributed to human activity. There are about 1,200 open landfills in the US.
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