Mootral - Studies show that the production of one litre of milk produces the equivalent of 900g of CO2. More than half of this is down to methane. The average cow emits between 80kg and 120kg of methane a year, equivalent to the annual carbon emissions from an average family car. ,a href="http://www.guardian.co.uk/environment/2009/feb/17/cadbury-dairy-milk-cows>via The Guardian>>