The total amount of waste deposited in US landfills (262 million tonnes) was underestimated by the US Environmental Protection Agency by as much as 140 million tonnes in 2012, according to a paper published online in Nature Climate Change. The study suggests that the associated methane emissions from landfill may also be greater than previously estimated.

Landfill sites emit major quantities of methane, a particularly potent greenhouse gas. Reducing emissions from these sites by capturing and combusting methane is a crucial part of climate change policy.

Jon Powell and colleagues analysed reported rates of waste disposal and operational data from 1,200 facilities across the US. They found 262 million tonnes of waste were disposed of by the facilities in 2012, about 140 million tonnes more than the US Environmental Protection Agency previously estimated. They also found waste disposal rates have been increasing by an average of 0.3% a year between 2010 and 2013.

Most of the waste ends up at open landfill facilities that are actively accepting new waste, and about 91% of landfill emissions in 2012 came from such sites. They found that the efficiency of methane capture was 17 percentage points greater at closed landfills than at open landfills, further underscoring the climatic impact of open waste sites.

The results suggest that the government must target efforts to reduce methane emissions at open landfill waste facilities. Furthermore, the authors argue that this study highlights the limitations of the government’s current approach to collecting waste disposal data, with significant implications for policy-based efforts to reduce emissions and tackle climate change.