Cattle and other farm animals are major sources of methane, a greenhouse gas many times more potent than carbon dioxide as a heat-trapping
gas.
Methane is released when they belch, pass
gas and make manure.
"If we can reduce emissions of methane, we can really help to slow global warming," said Ryan McCarthy, a science adviser for the California Air Resources Board, which is drawing up rules to implement the new law.
Livestock are responsible for 14.