A surprising amount of methane, a potent greenhouse gas of interest to scientists tracking climate change, comes from livestock, which accounted for 70 percent more emissions than the oil and gas industry, a new study shows.
The finding, based on satellite data collected in 2004, shows the U.S. Environmental Protection Agency sorely underestimated the amount of methane gas from cattle, pigs and other animals. The EPA also overestimated emissions from the oil and gas industry.
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The EPA estimates were extrapolated from national energy data, agricultural activities and an industry reporting system. The satellite data came from direct measurements of atmospheric methane by an instrument known as SCIMACHY – the Scanning Imaging Absorption spectrometer for Atmospheric Chartograph – aboard the European Space Agency's Envisat environmental spacecraft.
The satellite data showed livestock burping, flatulence and manure was the source of more than 13 million tons of methane gas in 2004, compared with the EPA's estimate of 9.7 million tons, according to a study published last month in the Journal of Geophysical Research: Atmospheres.
SCIMACHY measurements showed oil and gas industries released 7 million tons of methane gas into the atmosphere, compared to the EPA's estimate of 9.9 million tons.
Overall, the amount of methane gas emitted into the atmosphere by human activities in the United States was 33 million tons in 2004, the satellite data showed. The EPA's estimate for that same period was 31 million tons.
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After carbon dioxide, methane is the most widespread greenhouse gas tied to human activities.
"We need to know where is coming from in order to design effective emissions control policies," lead author Kevin Wecht, with Harvard University, said in an interview with the American Geophysical Union.
SCIMACHY stopped working in 2005, but the researchers said there is no reason to think that livestock's methane emissions have tapered off. In the past decade, emissions by oil and gas industries have increased, but how that has impacted overall concentrations of methane is not known.
NASA last week launched the Orbiting Carbon Observatory to make space-based measurements of atmospheric carbon dioxide. Initial results are expected in early 2015.
Image: Livestock accounted for 70 percent more methane gas emissions than the oil and gas industries in 2004. Credit: Flickr/kqedquest/AGU