Decomposing food waste releases thousands of tonnes of planet-warming methane gas in landfills in Lahore, as well as Buenos Aires, Delhi and Mumbai, new research shows.

With about 570 million tons of greenhouse gas emitted each year from both industrial and natural processes, the concentration of methane in the atmosphere has increased at a record pace, according to the US National Oceanic and Atmospheric Administration.

In some countries, the biggest source is agricultural fields and livestock – mainly cows, but also livestock and chickens. In the US, the oil and gas industry is largely responsible.

Yet there is another major global source – garbage. This is the case for Pakistan’s alarming levels of methane.

With data from a satellite-mounted detector showing high methane levels over cities in Pakistan, India, and Argentina, a team of scientists took a closer look to find out the sources of the emissions.

High-resolution satellite images taken in 2020 revealed that the methane came from landfills in Pakistan’s second-largest city Lahore, the Argentine capital Buenos Aires, and the Indian cities of New Delhi and Mumbai, according to the study published Wednesday in the journal Science Advances.

A landfill in Mumbai, for example, released about 9.8 tons of methane per hour, or 85,000 tons per year, according to the study’s findings. The landfill in Buenos Aires emitted about 250,000 tons annually – or half of the city’s total methane emissions.

“These observations can tell us where the big methane emissions are and where mitigation measures can be taken,” said co-author Joannes Maasakkers, an environmental scientist at the Netherlands Institute for Space Research. Remedial steps may include food composting or capturing methane for biogas.

Landfill waste – responsible for about 11% of global methane emissions – is expected to increase by about 70% by 2050 as the global population continues to rise, according to the World Bank.

Because methane is 80 times more potent than CO2 over a 20-year period, reducing “methane emissions now … could have a rapid impact on climate change,” Maasakkers said.

Previously, estimates of landfill emissions were made based on landfill volume and assumed rate of decay.

Satellite technologies are a boost for scientists, said Jean Bogner, a University of Illinois environmental scientist not involved in the research. This new approach helps to “adequately capture site-specific emissions, which for landfills can vary by orders of magnitude” depending on everything from soil conditions to whether mitigation measures are in place.