Study says it has a more accurate count of livestock methane emissions

According to the Environmental Protection Agency, the livestock industry is the second-biggest source of methane emissions in the country, but figuring out just how much gas the cattle, swine and poultry emit is difficult to pin down. "Current estimates of total livestock methane emissions may rely on outdated emission factors and do not fully consider feed intake and differences in animal diets, or the facilities used to store manure. These data gaps lead to large uncertainties in methane emission figures," the American Chemical Society reports. But a report just published in the ACS journal, Environmental Science & Technology, says a new approach could shed light on the accuracy of current data.

Livestock-produced methane comes not only from flatulence, which scientists call enteric emissions, but from fermentation of manure. Just how much is generated depends on the size of the animal, the species, the animals' diet, and how their manure is stored. Example: Cattle fed mostly grain generate less methane than grass-fed cattle.

A county-level map of methane emissions in the U.S.; click the image to enlarge it.

Researchers from Penn State analyzed the feed intake for cattle, as well as manure-storage practices for livestock at county and state levels. Their findings varied widely from currently reported numbers by organizations such as the European Emission Database for Global Atmospheric Research. "For example, the researchers found that the combined enteric and manure methane emissions from livestock in Texas and California were 36 percent less and 100 percent greater, respectively, than estimates by EDGAR. Based on their data, the researchers say that results from studies that use inaccurate distribution inventories to determine emissions sources should be cautiously interpreted," ACS reports.