Organic waste creates methane when decomposing in a landfill – and methane is a big environmental problem. Methane is a much more potent greenhouse gas than CO2 (although relatively short-lived) and is a major contributor to global warming. While we already have some options to deal with methane emissions, it’s still a big problem with a fifth of the global methane emissions coming from landfills.

Scientists at the Netherlands Institute for Space Research used satellite data from four big cities worldwide (Buenos Aires in Argentina, Delhi and Mumbai in India, and Lahore in Pakistan) and analyzed their methane emissions from landfills. These were 1.4 to 2.6 times higher than earlier estimates, which shows the urgent need to address this.

“Methane is odorless and colorless, so leaks are notoriously difficult to detect,” lead author Bram Maasakkers said in a statement. “But satellites are ideally suited for this. We detected super-emitters that pump large amounts of methane into the atmosphere. That is painful to watch as you can solve it with relatively little effort.”

A challenging greenhouse gas

Methane is the second largest anthropogenic contributor to the greenhouse effect after CO2 and has a major global warming potential over the next 100 years. Methane is about 30 times more potent per ton as a greenhouse gas than CO2. When released via human activity, it can be made less harmful by flaring and converting it to CO2.

While emissions from the fossil fuels sector have received considerable attention, this hasn’t been with methane emissions in the waste sector. And this could be a problem, as landfilled waste is expected to grow at more than double the rate of population growth between now and 2050 – increasing global solid waste methane emissions.

For their study, Maasakkers and the team of researchers used Tropomi, an instrument on the Copernicus Sentinel-5P satellite that tracks methane emissions across the planet every day. Buenos Aires, Delhi, Mumbai, and Lahore were the cities that stood out, with methane emissions about twice as high as estimated in global inventories.

The researchers then asked the satellite to zoom in, which showed that landfills account for a large share of methane emissions in those cities. The landfill in Buenos Aires, for example, emits 28 tons of methane per hour – that’s the same impact as 1.5 million cars. The other three landfills account for three, six, and 10 tons per hour, respectively.

“Methane has a lifetime of only about 10 years in the atmosphere, so if we act now, we will quickly see results in the form of less global warming. Of course, reducing methane emissions is not enough, we also need to limit CO2, but it does slow down near-term climate change,” Maasakkers said in a statement.

Last year, more than 100 countries agreed to reduce methane emissions by 30% by 2030 compared to 2020 levels. However, India and China, two of the largest methane polluters alongside Russia, didn’t sign the pledge. The researchers said they will continue looking at other landfill sites around the world in their future studies.

The study was published in the journal Science Advances.