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New report recommends nationwide effort to better estimate methane emissions

National Academies report suggests U.S. take "bold steps" to improve measurement, monitoring and inventories of methane emissions caused by human activities.

The U.S. should take bold steps to improve measurement, monitoring and inventories of methane emissions caused by human activities, according to a new report from the National Academies of Sciences, Engineering & Medicine. Better data on methane — a greenhouse gas that contributes to air pollution and threatens public and worker safety — would help inform decisions related to climate, economics and human health, the report says.

"Methane is getting more attention because it is a potent, short-lived greenhouse gas that is increasing," said James W.C. White, professor of geological sciences at the University of Colorado-Boulder and chair of the committee that conducted the study and wrote the report. "There have been recent advances in our abilities to measure and monitor methane from its many sources, and now we need to strengthen and interlink these different approaches."

Anthropogenic sources of methane emissions span various sectors of the economy, such as energy, agriculture and waste disposal. There are a variety of reasons, beyond climate change, to measure, monitor and track methane emissions, the committee said. For example, monitoring methane emissions is important to protecting the health and safety of workers in industries such as coal mining, and recovery of methane can have an economic benefit as a source of energy.

In general, there are two approaches to estimate methane emissions. The top-down approach estimates emissions using observations of atmospheric methane concentrations and models that simulate their transport from the source to the observation location. The bottom-up approach measures emissions at the scale of individual methane emitters, such as natural gas wells or cattle farms, and uses those results to extrapolate emissions at regional and national scales.

In some cases, the estimates produced by these two methods differ significantly, potentially revealing missing emission sources, for example, or problems with the atmospheric sampling, the report says. To address such discrepancies, the report recommends a national research effort to strengthen the two methods to improve accuracy, better attribute emissions to specific sectors and processes and detect trends.

Currently, the Greenhouse Gases Inventory (GHGI) serves as the main source of information for emissions in the U.S., with emissions reported at a national scale annually. As a complement to GHGI, the report says the U.S. should establish and maintain a gridded inventory that presents data at finer spatial (i.e., size and distance) and temporal (i.e., time) scales.

Such an inventory, with values for major sources of emissions within the grid of a location, is necessary for scientists to make detailed comparisons between the top-down and bottom-up estimates of methane emissions and would address the needs of state and local policy-makers who require more detailed information than currently available, the committee said.

Numerous inventories that track methane emissions over time and link them to their specific source have been developed to address specific needs. GHGI trends in the data help policy-makers assess the effectiveness of national-scale policy initiatives. State-level inventories are more detailed than GHGI, allowing for state policy to be tailored. Individual facilities or companies use inventories for corporate sustainability reporting and to make informed investment and risk decisions, according to the announcement.

As the science evolves and methodologies to estimate emissions become outdated, the report emphasized that it is important to keep practices consistent with the best scientific understanding and current engineering practice.

An advisory group should be established to guide how new science can be incorporated into improving GHGI. The group could be facilitated by U.S. Environmental Protection Agency and the National Oceanic & Atmospheric Administration (NOAA) and should include experts from academia, industry, policy, other federal agencies and non-government organizations. Any changes to GHGI resulting from these activities should be clearly communicated to the public, the committee said.

The study was sponsored by EPA, the U.S. Department of Energy, NOAA and the National Aeronautics & Space Administration.

The National Academies of Sciences, Engineering & Medicine comprises private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology and medicine.

Copies of "Improving Characterization of Anthropogenic Methane Emissions in the United States" are available at www.nap.edu.

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