Livestock were the single largest source of methane gas emissions in the United States in 2004, releasing 70 percent more of the powerful greenhouse gas into the atmosphere than the oil and gas industry, according to a new study.

The new study based on satellite data from 2004 provides the clearest picture yet of methane emissions over the entire U.S. It shows human activities released more of the gas into the atmosphere than previously thought and the sources of these emissions could be much different than government estimates.