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Scientists have warned that landfills are releasing large amounts of Earth-warming methane into the atmosphere through the decomposition of waste.
Using satellite data from four major cities – Delhi and Mumbai in India, Lahore in Pakistan and Buenos Aires in Argentina – the researchers found that urban emissions in 2018 and 2019 were higher than previously estimated 1.4 to 2.6 times higher.
The study, published in Science Advances, aims to help local governments conduct targeted efforts to limit global warming by identifying specific sites of primary concern.
When organic waste such as food, wood or paper breaks down, it releases methane into the air.
Landfills are the third largest source of methane emissions globally, after oil and gas systems and agriculture.
Although methane only accounts for about 11 percent of greenhouse gas emissions and persists in the air for about a dozen years, it absorbs 80 times more heat in the atmosphere than carbon dioxide. Scientists estimate that at least 25% of today’s warming is caused by methane produced by human activity.
“This is the first time that high-resolution satellite imagery has been used to look at a landfill and calculate its methane emissions,” said Joannes Maasakkers, an atmospheric scientist at the Netherlands Institute for Space Research and lead author of the study.
“We found that these landfills are relatively small compared to the size of cities, but account for a significant portion of total emissions in a given area,” he said.
Satellite data for detecting emissions is still a relatively new field, but it’s used more for looking at gases around the world. That means more independent groups are tracking greenhouse gases and identifying big emitters, where previously local government data was the only source available.
Euan Nisbet, a geoscientist at Royal Holloway, University of London, said: “This new work shows how important it is to better manage landfills, especially in a country like India, where landfills regularly catch fire and emit many harmful pollutants.”, who was not part of the study.
Smoke blanketed New Delhi for days after a huge landfill caught fire earlier this year, as the country was in the midst of an extreme heatwave with temperatures exceeding 50 degrees Celsius. At least two other landfill fires have been reported in India this year.
Mr Nisbet added that newer satellite technology combined with ground-based measurements made it easier for researchers to identify “who is polluting the world”.
A recent analysis by the International Energy Agency found that China and India are the world’s biggest methane polluters.
At last year’s UN climate conference, 104 countries signed a pledge to cut methane emissions by 30% by 2030 compared to 2020 levels. Neither India nor China is a signatory.
The authors plan to conduct more research on landfills around the world in future research.
“This is a fast-moving field, and we expect more interesting data to emerge soon,” Mr Maasakkers said.
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