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Wasted food rotting in landfills is a large and growing source of planet-warming methane emissions in the US, according to a report that quantifies these emissions for the first time. Cutting food waste is the best way to reduce these emissions.

Landfills make up of US methane emissions, the third largest source after fossil fuel production and livestock burps. This landfill methane is produced by decaying organic matter, such as paper and food. More than one-third of all food produced in the US is never consumed, and most of that wasted food ends up getting thrown away.

at the US Environmental Protection Agency (EPA) and her colleagues estimated the methane emissions generated by this food using data collected by operators of more than 2600 landfills between 1990 and 2020. They modelled methane emissions from the waste by considering a number of factors, including the different types of landfills and rates of decay of various kinds of organic matter.

They found that in 2020 alone, food waste in US landfills released enough methane to have a global warming effect equivalent to 55 million tonnes of carbon dioxide over the next 100 years 鈥� about as much as 12 million gasoline-powered cars generate in a year. Overall, food waste made up almost 60 per cent of landfill methane emissions, despite accounting for only about a quarter of overall waste in those landfills.

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The report also found that between 1990 and 2020, emissions from food waste nearly tripled, even as overall methane emissions from landfills saw a substantial decline due to expanded methane capture systems. The researchers attributed this increase to a rise in the quantity of food waste, as well as the fact that much of the food waste in a landfill decays before capture systems are installed once the site is full.

at the environmental non-profit World Resources Institute in Washington, DC says the finding clearly shows the importance of reducing food waste, not only to curb methane emissions from landfills, but also to cut the greenhouse gas and land use impacts associated with producing those surplus nutrients.

Alongside the study, the EPA of the most environmentally preferable approaches to dealing with food scraps. It found that reducing waste at every part of the supply chain and donating anything leftover are most helpful. Using excess food for animal feed, composting it or digesting it to produce biogas are also options, although they only have small or neutral environmental benefits.

They deemed incinerating food, sending it down the drain or putting it in a landfill as the worst ways to deal with waste.