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Investigating methane emissions in the San Juan Basin

This map shows how methane levels differ from average background levels for 2003 to 2009, as derived from remote sensing data from the European Space Agency’s SCIAMACHY instrument. Purple and dark blue areas are below average, pale blue and green are close to normal, and yellows and red indicate higher-than-normal anomalies. Note that the San Juan Basin near the Four Corners region is the only red spot on the map. Credit: NASA/JPL-Caltech/University of Michigan.

A coordinated observing campaign uncovered the causes of an unexpected methane plume spotted by satellite.

Methane is a potent greenhouse gas emitted by both natural sources and processes (such as wetlands, geological seeps, and biomass burning) and human activities (including agriculture, waste and landfills, and fossil fuel extraction). Sources of regional and global methane pollution can be tracked through emission inventories, atmospheric in situ measurements, and remote sensing observations, allowing scientists to detect and study methane emissions and how they are changing.1 A major fossil fuel-producing region in the U.S. Southwest came to national attention in 2014 when a satellite spotted an unexpectedly large methane plume over the region,2 prompting scientists to investigate what became known as the largest local methane hotspot in the country.

In 2015, researchers funded by NASA, NOAA, and NSF used ground and airborne instrumentation throughout the San Juan Basin to further study the plume, leading to new research published in 2020.3 These detailed observations showed that the methane cloud was not a persistent, undiscovered emissions hotspot as initially believed. Instead, the plume was the result of nightly atmospheric conditions and local topography trapping industrial and natural methane emissions in the basin overnight, captured by a daily midmorning satellite overpass. Accumulated emissions were later flushed out by surface winds throughout the day, meaning that the plume was not as large and persistent as it initially appeared in satellite data.

The in situ ground and airborne measurement campaign was carried out by scientists from NOAA and the University of Colorado, Boulder, in collaboration with DOI, the Bureau of Land Management, state and local governments, the Southern Ute Indian Tribe Air Quality Program and Department of Energy, and the Navajo Nation Environmental Protection Agency. Results demonstrated that sustained, coordinated measurements are important for identifying the sources and impacts of apparent pollution spikes, particularly those that vary over time, and can help inform actions and policies to reduce emissions. Future satellite measurements of methane collected more frequently, such as hourly data from a geostationary satellite, could provide an improved picture of methane plumes that vary over time.

1 Jacobson, A. R., J. B. Miller, A. Ballantyne, S. Basu, L. Bruhwiler, A. Chatterjee, S. Denning, and L. Ott, 2018: Chapter 8: Observations of atmospheric carbon dioxide and methane. In Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report [Cavallaro, N., G. Shrestha, R. Birdsey, M. A. Mayes, R. G. Najjar, S. C. Reed, P. Romero-Lankao, and Z. Zhu (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 337-364,

2 Kort, E.A., C. Frankenberg, K.R. Costigan, R. Lindenmaier, M.K. Dubey, and D. Wunch (2014), Four corners: The largest US methane anomaly viewed from space, Geo phys. Res. Lett., 41, 6898-6903,

3 Pétron, G, et al. 2020. Investigating large methane enhancements in the U.S. San Juan Basin. Elem Sci Anth, 8: XX.