Space-based measurements have revealed a previously unknown cloud of methane hovering over a coal production region on and near the Navajo Nation.
The cloud, which scientists are calling a “hot spot,” covers 2,500 square miles, about half the size of Connecticut, near the Four Corners intersection of Arizona, Colorado, New Mexico and Utah. It was reported in a study released on October 9 in the journal Geophysical Research Letters.
The finding is important partly because methane is a greenhouse gas more potent, and less understood, than carbon dioxide. It can be produced from agriculture, forest fires and the mining and processing of fossil fuels. In this case the sources include heavy production of a fuel called coalbed methane, which exists as a gas in the pores and cracks of coal deposits, as well as emissions from two power plants well known for their pollution: the on-reservation Four Corners Power Plant and the neighboring San Juan Power Plant.
“Both methane and carbon dioxide warm the climate,” explained Manvendra Dubey, a climate scientist at the Department of Energy’s Los Alamos National Lab and one of the study authors. “Methane, if you leak it, has a 10-year lifespan in the atmosphere compared to hundreds of years for carbon dioxide. But the warming potential is very high.”
Although the scientific community hasn’t been able to agree on how much methane in the atmosphere is too much, “everyone agrees emitting methane at the high rates we are is not a good thing,” Dubey said.
The new study's lead author, Eric Kort of the University of Michigan, pointed out that the observation period predates the widespread use of hydraulic fracturing, known as fracking, near the hot spot. So the methane emissions didn’t come from fracking, but instead from leaks in previously established natural gas production and processing.
Nevertheless, fracking is now well under way in the Four Corners area, and methane emission from fracking is another matter of scientific debate. The new results help provide a baseline for tracking new emissions.
The researchers used observations by the European Space Agency’s Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). A Los Alamos ground station provided independent validation. In each of the seven years from 2003 to 2009, the Four Corners area released about 650,000 tons of methane into the atmosphere.
The Four Corners methane plume is by far the largest visible from space over the continental United States, and makes up 10 percent of the U.S. Environmental Protection Agency’s (EPA) estimate of the country’s methane emissions from natural gas.
Other regions, especially the Texas-Oklahoma area and central California, also show elevated methane levels. Those are probably associated with emissions from oil, gas, grazing animals and agriculture, the study authors pointed out. Those signals are less than half the strength of the Four Corners hot spot, though, and they wax and wane through the seasons. The Four Corners hot spot persisted from 2003 through 2009, in all seasons.
That the 2,040-megawatt Four Corners Power Plant would be implicated in the discovery is not surprising. Regulators have known for some time that it’s a significant polluter. The plant’s primary owner, Arizona Public Service, recently opted to shut down three of its five units rather than install expensive pollution controls in order to meet new EPA air quality rules.
Facing similar regulatory pressure, the San Juan Power Plant in Farmington, New Mexico, is proceeding with a plan to shut down two of four units and install new natural gas facilities.
Dubey pointed out that the hot spot discovery will assist regulators in two main ways moving forward. First, the data reveal that the EPA previously under-estimated the Four Corners methane plume by about half, and the new information will be helpful as the agency revises its estimates. Second, the space-based observation technique means that leaks won’t likely escape attention in the future.
“We were able to show that satellites can look at these signals almost everywhere,” Dubey said.