A study led by researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has found that the Environmental Protection Agency (EPA) is underestimating methane emissions from landfills, urban areas, and U.S. states. The researchers used 2019 satellite observations and an atmospheric transport model to generate a high-resolution map of methane emissions, which showed that EPA estimates are lower than actual emissions. Methane is the second largest contributor to climate change behind carbon dioxide, making it crucial to accurately quantify emissions from different sources.
The research, published in Atmospheric Chemistry and Physics, involved collaboration between scientists at Harvard and an interdisciplinary team of researchers from around the world. The study focused on landfills, which are considered the third-largest source of human-caused methane emissions in the U.S. The EPA’s estimates for landfill emissions are based on a bottom-up accounting method that does not always align with observations of atmospheric methane. Nesser and her colleagues used a top-down approach that combined satellite observations with an atmospheric transport model to trace emissions back to the ground.
The researchers found that methane emissions from landfills were 51% higher than EPA estimates, with emissions from 95 urban areas being 39% higher and emissions from the 10 states with the highest methane emissions being 27% higher. The study also highlighted discrepancies in methane collection efficiency at landfills, with actual methane levels being much higher than EPA estimates. The researchers identified one-off events such as construction projects or temporary leaks as potential sources of increased methane emissions that are not captured by EPA estimates.
The study also compared the researchers’ analysis to the EPA’s state-level greenhouse gas inventories and found 27% higher methane emissions from the top 10 methane-producing states, with significant increases in Texas, Louisiana, Florida, and Oklahoma. The researchers identified the top 10 cities with the highest urban methane emissions, which were found to have 58% higher emissions than previously estimated. The researchers hope that future work will provide more clarity on the sources of methane emissions and how they are changing over time.
The importance of understanding methane emissions is emphasized by Daniel Jacob, the senior author of the paper and Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering at SEAS. The researchers plan to continue monitoring U.S. methane emissions using new high-resolution satellite observations and working with the EPA to improve emission inventories. The study was supported by the NASA Carbon Monitoring System (CMS) and the Harvard Climate Change Solutions Fund and included contributions from several researchers from different institutions.
In conclusion, the study led by researchers at Harvard SEAS has shown that the EPA is underestimating methane emissions from landfills, urban areas, and U.S. states. The researchers used satellite observations and an atmospheric transport model to generate a high-resolution map of methane emissions, revealing discrepancies between EPA estimates and actual emissions. The study highlights the importance of accurately quantifying methane emissions, as methane is a significant contributor to climate change. Future work will focus on identifying sources of methane emissions and improving emission inventories in collaboration with the EPA.
