A satellite that measures greenhouse gases in the atmosphere has found a small "hotspot" of the heat-trapping methane gas, which contributes to global warming, over the southwestern United States.

Scientists from the National Aeronautics and Space Administration and the University of Michigan revealed that the hotspot is responsible for the production of the largest concentration of methane over the country, based on an analysis of data from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), an instrument of the European Space Agency (ESA) that measured greenhouse gases from 2002 to 2012.

Using SCIAMACHY data covering seven years, scientists found that the hotspot produced about 0.59 million metric tons of atmospheric methane and this is about thrice the estimate for the same area in the ground-based database of the European Union.

The hotspot, which spans about 2,500 square miles or about half the size of the state of Connecticut, is located near the intersection of New Mexico, Arizona, Colorado and Utah and appears as a bright red blip in the satellite image that used data from 2003 to 2009.

The findings, described in "Four Corners: The largest U.S. methane anomaly viewed from space," which was published in the journal Geophysical Research Letters on Oct. 9, suggest that the U.S. Environmental Protection Agency and other agencies may have underestimated the leaks of the natural gas.

"This underestimated source approaches 10 percent of the EPA estimate of total U.S. CH4 emissions from natural gas," the researchers wrote.

Although the higher level of methane does not pose health issues to the residents, scientists are concerned about increasing amounts of the gas because, just like carbon dioxide, methane also contributes to the overall warming of the Earth, which is associated with extreme climate events, loss of habitat and other unwanted events. Because methane is colorless and odorless, tracking leaks also has its challenges.

Eric Kort, study author and atmospheric scientist from the University of Michigan, said that the methane may have come from leaks as natural gas is extracted from coal beds. Hydraulic fracturing may not have caused the excessive release of methane because fracking was not yet widely used near the hotspot during the study period.

"The results are indicative that emissions from established fossil fuel harvesting techniques are greater than inventoried," Kort said. "There's been so much attention on high-volume hydraulic fracturing, but we need to consider the industry as a whole."

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