By Georgina Gustin, Inside Climate News.

Despite heavy pushback from the state's livestock producers, California Gov. Jerry Brown last month signed a law aimed at cutting methane emissions from cattle operations, the largest source of heat-trapping methane in the country's biggest dairy-producing state.

More than half of California's methane emissions come from dairy and beef operations, specifically from cow manure and belching, mostly from dairy cows. But the state's powerful dairy industry has successfully blocked methane regulation for the past decade.

Now, as the state works toward meeting the nation's most aggressive greenhouse gas emissions targets, the livestock sector and methane—with its potent atmospheric warming power—will contend with regulation for the first time.