Reducing short-lived climate pollutants like methane (CH4) is key for minimizing the risk of crossing the 2°C threshold. Studies have suggested that CH4 from U.S. dairies is up to 50% greater than U.S. Environmental Protection Agency inventory estimates. In 2013, inventory estimates based on U.S. EPA methodology attributed 45% of the California’s CH4 budget to the dairy industry (20% from enteric fermentation and 25% from manure management). The California law, enacted on Sept 19 2016, requires manure emissions to be reduced by 40% of 2013 levels by 2030. The objectives of our study were to measured CH4 emissions from two California dairies to: 1) compare the performance of different measurement methods; 2) measure CH4 emissions from enteric fermentation and manure management separately and to compare these with U.S. EPA inventory estimates; and 3) compare between dairies to determine mitigation opportunities. Measurements were conducted in summer using three independent measurement techniques: one aircraft-based and two ground-based (drive-by and open-path) and in winter using open-path.