New analyses of satellite observations over the American Southwest have provided a detailed view of a persistent, large-scale methane anomaly. Data from the European Space Agency’s Sentinel satellite family, equipped with advanced atmospheric monitoring instruments, are offering an unprecedented perspective on the scale and nature of greenhouse gas releases from this region. These modern instruments confirm and build upon earlier findings that identified the area as the most significant concentration of methane in the United States.

The concentration of methane, a powerful greenhouse gas, is centered on the Four Corners region where Arizona, Colorado, New Mexico, and Utah meet. This area is home to the San Juan Basin, one of the most productive natural gas fields in North America. The data underscores the critical role that new satellite technology plays in identifying and quantifying emissions of climate-warming pollutants. Understanding the precise sources and atmospheric behavior of this methane cloud is crucial for developing effective mitigation strategies and for the U.S. to meet its climate goals, as methane is responsible for approximately 30% of the global temperature rise since the Industrial Revolution.

Advanced Orbital Observation Systems

Modern atmospheric monitoring relies on a sophisticated suite of instruments orbiting Earth, with the Copernicus Sentinel program playing a leading role. The Sentinel-5P satellite, specifically, is a key asset in this effort. Launched in 2017, its mission is dedicated to monitoring the atmosphere. It carries the state-of-the-art TROPOspheric Monitoring Instrument (TROPOMI), which can map a multitude of trace gases, including methane, nitrogen dioxide, and carbon monoxide, on a global scale every 24 hours. TROPOMI’s ability to achieve high spatial resolution allows scientists to pinpoint emission sources on the ground with greater accuracy than ever before.

While Sentinel-5P is designed for atmospheric chemistry, other satellites in the constellation, like Sentinel-2, have also demonstrated surprising capabilities. Though primarily intended for land observation, researchers have developed methods to use Sentinel-2’s multispectral instrument to detect large methane plumes from specific point sources, such as oil and gas facilities. This multi-satellite approach provides both a wide-area view from Sentinel-5P to identify hotspots and a higher-resolution tool with Sentinel-2 to zoom in on potential leaks, creating a powerful, tiered system for tracking greenhouse gas pollution from space.

Anatomy of a Methane Hotspot

The Four Corners hotspot is a long-documented atmospheric feature. The initial discovery was made public in a landmark 2014 study by scientists from NASA and the University of Michigan. Using data gathered between 2003 and 2009 from Sentinel-5P’s predecessor, the SCIAMACHY instrument, they identified a consistent methane concentration covering about 2,500 square miles. The study calculated that the region was releasing approximately 0.59 million metric tons of methane annually, an amount nearly 3.5 times higher than was estimated in emission inventories used at the time.

Atmospheric and Topographic Influences

Subsequent research has refined our understanding of the hotspot, revealing that it is not a static, hovering cloud. A 2020 study involving NOAA and the Cooperative Institute for Research in Environmental Sciences (CIRES) conducted an intensive field campaign using aircraft and ground-based sensors. They found that the satellite observations were strongly influenced by local weather patterns and topography. In the morning, cool air settles in the basin, trapping emissions from the previous night close to the ground. This concentrated layer of methane is what the satellites, which typically have a morning overpass time, were detecting. As the day progresses and the ground warms, winds tend to disperse the plume, reducing the surface concentration. This finding clarifies that the hotspot is a persistent emissions area subject to diurnal atmospheric cycles, rather than a single, unchanging plume.

Pinpointing a Region’s Emitters

The primary driver of the Four Corners anomaly is the region’s extensive fossil fuel infrastructure. The San Juan Basin is the most productive area for coalbed methane extraction in the country. This process involves pumping large volumes of water out of coal seams to release trapped natural gas, which is primarily composed of methane. During extraction, processing, and transportation through a vast network of wells, pipelines, and compressor stations, a certain amount of gas escapes into the atmosphere. These “fugitive emissions” are the main source of the methane hotspot.

The 2014 study noted that its data, collected before 2010, predated the widespread boom in hydraulic fracturing, or “fracking,” in the area. This indicated that the emissions were linked to the conventional, long-standing oil and gas activities. The subsequent 2020 field study provided more direct attribution, finding that between 66% and 75% of the observed methane came directly from natural gas and coalbed methane operations. Researchers were able to fly over the region and identify hundreds of individual emission sources, including well pads, processing plants, and storage tanks. A smaller portion of the emissions, estimated at less than 10%, was attributed to natural geologic seeps from coal outcrops.

Global and Local Implications

The significance of the Four Corners hotspot extends far beyond the Southwest. Methane is a formidable greenhouse gas. According to the Intergovernmental Panel on Climate Change (IPCC), it possesses a global warming potential more than 80 times that of carbon dioxide over a 20-year period and around 30 times over a century. Its shorter atmospheric lifetime means that reductions in methane emissions can have a much more immediate impact on slowing the rate of global warming. The massive, undercounted emissions from this single basin suggest that national and global inventories may not fully account for all sources, complicating efforts to model and combat climate change accurately.

This persistent emission zone also highlights the challenge and opportunity for the energy industry. The leaked methane represents lost product, and capturing it could offer both economic and environmental benefits. For regulators, the data provided by satellites like Sentinel-5P is becoming indispensable for monitoring compliance with emissions standards and for holding polluters accountable. The information allows for targeted action to repair leaks and improve operational practices, which is essential for the industry to reduce its climate footprint.

The Path to Mitigation and Monitoring

The continued surveillance of the Four Corners region by satellites is a critical component of climate mitigation efforts. The daily global coverage from Sentinel-5P provides a consistent, reliable stream of data that allows scientists and regulators to monitor for changes in emission levels over time. As policies are implemented or industry practices change, these satellites can verify their effectiveness. Furthermore, this data serves as an early-warning system, capable of detecting new leaks or unexpected increases in emissions that may require on-the-ground inspection and repair.

The United Nations and other international bodies are now integrating satellite data into global methane monitoring systems, such as the International Methane Emissions Observatory’s MARS initiative. This system uses Sentinel-5P’s broad scans to detect large plumes and then can trigger higher-resolution observations from other satellites to investigate further. By making this information publicly available, these programs create transparency and empower governments, researchers, and the public to take informed action. The story of the Four Corners hotspot, from its initial discovery to its ongoing monitoring by a new generation of satellites, serves as a powerful example of how space-based technology is essential for protecting the climate on Earth.