Emissions from greenhouse gas methane have risen higher in the U.S. than previous estimates and models predicted, NBC News reported.

According to a new study, the level of greenhouse gas methane caused by industrial activity is about 1.7 higher than the estimates of the Emissions Database for Global Atmospheric Research (EDGAR). Models from the Environmental Protection Agency (EPA) reported similar findings and 1.5 times higher.

Perhaps one of the most bizarre reasons for heightened methane emissions is the flatulence of cows. According to the EPA, methane accounts for 20 times the impact on global warming than carbon dioxide does over the span of 100 years.

"When we measure methane gas in the atmosphere, we are seeing the sum total contribution of all the emissions that would have happened at the surface," said study lead author Scot Miller, a Harvard University graduate student. "And if we analyze those measurements very carefully we can get a better understanding of the total amount of methane that comes from a large region, or say comes from the United States."

Miller and his fellow researchers published their work in the journal Proceedings of the National Academy of Sciences.

"What we find," Miller said of the team's results, "is that our total estimate for the United States does not equal the sum of the parts from the Environmental Protection Agency."

David Allen, a chemical engineer at the University of Texas at Austin, authored a similar paper for PNAS on natural gas production. Not involved with Miller's study, he told NBC News it is an "important contribution" to efforts to lower methane emissions, which pose a threat just like CO2 does.

"Fossil fuel production and processing and animal husbandry are large and complex activities, with a large number of potential sources," he said. "So, a logical follow-up question is which sources within these sectors are responsible for the emissions."

Miller said gas and oil companies are the chief causes of heightened methane, which also goes hand in hand with propane, the gas that powers grills. While cows emit methane, they cannot also produce propane. In states like Texas and Oklahoma, both gases have been problematic.

"And it turns out when we measure high methane gas in the atmosphere over Texas and Oklahoma, we also generally measure high propane gas levels," Miller said. "And similarly, if we measure low methane gas, we typically also measure low propane over Texas and Oklahoma."