A recent study conducted by researchers from Harvard and seven other institutions suggests that methane emissions in the United States could be 1.5 times greater than the amount estimated by the U.S. Environmental Protection Agency, and 1.7 times greater than that estimated by the Emissions Database for Global Atmospheric Research.
The findings, published last week in Proceedings of the National Academy of Sciences, uses an innovative method for measuring methane emissions that its authors hope will result in a more accurate estimate.
“With this research, we want to get a better idea of greenhouse gas emissions in the United States and get an understanding of what the largest players are in the emission that we see,” said lead author Scot M. Miller ’07, a doctoral student in Earth and Planetary Sciences at the Graduate School of Arts and Sciences.
Methane emissions are a byproduct of the oil and gas industries, ruminants such as cattle and sheep, landfills, waste water treatment plants, and coal mining.
While both the EPA and this new study agree that the oil and gas industries and ruminants are the two largest sources of emissions in the United States, they differ in their method of estimating methane emissions. The EPA’s bottom-up, or counting type, method looks at all possible sources for methane emissions in order to estimate the emissions factor, which is the amount of methane believed to be coming from an average ruminant or oil and gas facility on a given day.
Researchers in this new study employed a top-down method, which attempts to calculate the total methane emissions in the United States and then works backwards to identify the geographic locations responsible for those emissions.
“The advantage of using a top-down method is that we get a very strong constraint on the total amount of methane emitted over a large region or over an area as large as the United States,” Miller said.
Besides employing this innovative method, the study also provides some insight into how society might combat the problem of rising methane emissions.
“The results of this study may motivate increased consideration of efforts to mitigate methane emissions by looking at their sources and finding socially and economically acceptable solutions that reduce the emission,” said co-author Marc L. Fischer, who works in the Environmental Energy Technologies Division of Lawrence Berkeley National Laboratory.
In terms of future studies, Miller cited the importance of learning how emissions have changed over time.
“If we can examine methane emission from 2007 all the way up to 2013, we can get a better handle on how emissions may have changed over time and how [the] expansion of the fossil fuel industry could’ve affected total emission throughout the United States,” said Miller.