Methane emissions are greatly underestimated by the EPA

Methane emissions from landfills, urban areas, and across several U.S. states are substantially underestimated by the Environmental Protection Agency (EPA). This is the conclusion of a study by researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).

The experts used advanced satellite data from 2019 combined with an atmospheric transport model to create a detailed map of methane emissions across the United States. 

Underestimated methane emissions

The analysis showed that emissions from landfills were 51% higher than EPA estimates for the same year. In addition, methane emissions from urban areas were 39% higher, while those from the ten highest methane-emitting states were 27% higher compared to EPA estimates.

“Methane is the second largest contributor to climate change behind carbon dioxide so it’s really important that we quantify methane emissions at the highest possible resolution to pinpoint what sources it is coming from,” said lead author Hannah Nesser, a former PhD student at SEAS and currently a NASA Postdoctoral Program (NPP) Fellow in the Carbon Cycle & Ecosystems Group at the Jet Propulsion Laboratory.

Underreporting in methane emissions 

The study reveals a significant underreporting in methane emissions, particularly from landfills, which the EPA ranks as the third-largest source of human-caused methane emissions in the United States.

The EPA’s method relies on self-reported data from facilities that emit high levels of greenhouse gasses and uses a formula based on the volume of trash received to estimate emissions. This bottom-up approach is often inconsistent with top-down observational data gathered from atmospheric measurements.

“Our research shows that these facilities are losing more methane than they think,” Nesser said. “The EPA uses 75% efficacy as the default for methane collection, but we find that it’s actually much closer to 50%.”

Discrepancies in EPA models

Moreover, the scientists found that occasional events like construction or temporary leaks at landfill sites, which can significantly increase methane emissions, are not adequately accounted for in the EPA’s models. 

The study also highlighted discrepancies at the state level, particularly in Texas, Louisiana, Florida, and Oklahoma, which are among the top methane emitters. Notably, Texas alone is responsible for 21% of U.S. anthropogenic methane emissions, largely due to its extensive oil and gas industry.

Methane emissions from cities

The scientists also discovered that methane emissions in the 10 cities with the highest levels of urban methane output are, on average, 58% greater than what was previously estimated. These cities include New York, Detroit, Atlanta, Dallas, Houston, Chicago, Los Angeles, Cincinnati, Miami, and Philadelphia.

“All of these places have a different profile of emission sources, so there’s no one thing driving the methane underestimate across the board,” Nesser said.

“This research highlights the importance of understanding these emissions,” added senior author Daniel Jacob, a professor of atmospheric chemistry and environmental engineering at SEAS. “We plan to continue to monitor U.S. emissions of methane using new high-resolution satellite observations, and to work with the EPA to improve emission inventories.”

Broader study implications 

The implications of these findings are significant, urging a reevaluation of how methane emissions are estimated and reported. Accurate data is crucial for effective environmental policy-making and for strategies aimed at mitigating climate change. 

By refining how methane emissions are measured, researchers hope to foster better regulatory practices and more effective mitigation strategies to combat this potent greenhouse gas.

Dangers of methane 

Methane is a potent greenhouse gas, considerably more effective at trapping heat in the atmosphere than carbon dioxide, especially in the short term. Its significant impact on global warming makes it a critical concern for climate change. 

Sources

Methane emissions come from a variety of sources, including the decay of organic waste in landfills, agriculture (especially from the digestive processes of grazing animals), and the production and transport of coal, oil, and natural gas.

Climate change

One of the dangers of methane is its ability to rapidly accelerate climate change. It has a much higher heat-trapping capability per molecule compared to carbon dioxide, so even small amounts can have a significant effect on atmospheric temperatures. 

This contributes to the increasing global temperatures, which can lead to more severe weather events, melting polar ice, rising sea levels, and disrupting ecosystems.

Ground-level ozone

Furthermore, methane contributes to the formation of ground-level ozone, a harmful air pollutant. Exposure to ozone can lead to serious respiratory health issues and other health problems in humans and animals. It also affects crops and other vegetation, potentially reducing agricultural yields.

Reducing methane emissions 

The short atmospheric lifetime of methane – about 12 years – compared to carbon dioxide, however, means that taking action to reduce methane emissions can quickly benefit the atmosphere. Thus, addressing methane leaks and emissions is seen as a crucial and effective strategy for slowing the rate of global warming in the near term. 

Efforts to capture methane from sources like landfills and livestock operations can not only mitigate the effects on climate change but also harness methane as a source of energy, providing a cleaner alternative to other fossil fuels.

The study is published in the journal Atmospheric Chemistry and Physics.

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