Cows and pigs produce a large share of planet-warming methane. A new tax is part of a plan to clean that up. Cows and pigs produce a large share of planet-warming methane. A new tax is part of a plan to clean that up. Global Warming, Greenhouse Gas Emissions, Agriculture and Farming, Methane, Manure, Livestock, Regulation and Deregulation of Industry, Denmark, climatefix24 NYT > Science