Methane is one of the most potent greenhouse gases, second only to carbon dioxide in its ability to absorb thermal radiation. It is naturally produced by wetlands, and humans emit methane in large quantities through the use of oil and gas for energy, livestock farming, coal mining, and landfills.
In recent years, methane levels have been on the rise. Global atmospheric levels rose 1%–2% in the 1970s and 1980s, leveled out in the 1990s, and then continued to rise in the 2000s. Although scientists have established this increase, they have found it more challenging to determine which anthropogenic sources are most responsible for methane emissions because sources often overlap and are difficult to quantify.
Here Turner et al. obtained data from government sources, including the Greenhouse Gas Inventory of the U.S. Environmental Protection Agency (EPA), to determine how much methane the United States is contributing to global emissions. They also used data from the Greenhouse Gases Observing Satellite (GOSAT), launched into low orbit in January 2009. By examining GOSAT data for the United States from January 2010 to January 2014, the researchers could determine how methane levels fluctuated over every region in the country.
U.S. EPA inventory data showed that emissions from oil and gas and from livestock each accounted for about a third of the methane produced by the United States, while landfill waste accounted for 21%–22% and coal was responsible for 10%–13% of methane emissions.
The researchers found that U.S. methane emissions have increased by more than 30% in the past decade, making the United States a hefty contributor to the global rise in emissions. It seems the increase is largely caused by sources in the central United States—the only region in the nation to show statistically significant increases in methane production. Recent increases in oil and gas production as well as shale gas production may possibly account for this change, but other sources could be involved as well. (Geophysical Research Letters, doi:10.1002/2016GL067987, 2016)
—Shannon Kelleher, Writer Intern
Citation: Kelleher, S. (2016), U.S. methane emissions on the rise, Eos, 97, doi:10.1029/2016EO048071. Published on 22 March 2016.