DON'T believe the petrol-heads' propaganda - cows do not produce more carbon dioxide than cars. In a bid to demystify carbon footprinting for Huntingdonshire businesses, Simon Best from Envirowise - a Government-funded programme dedicated to putting sustainable use of resources at the heart of business practice - compared four common sources of greenhouse gas emissions. He explained that emissions were measured as CO2 equivalents that included the length of time they remained in the atmosphere. "Methane is 21 times more potent a greenhouse has than CO2, and sulphur hexafluoride is 23,900 times more potent because it stays in the atmosphere for so long," he said. One hundred company cars generate the equivalent of 540 tonnes of CO2 in a year, while 100 cows produce in methane the equivalent of 307 tonnes over the same period. But it takes a 200 megaWatt coal-fired power station just 100 minutes to throw out 1,615 tonnes. One hundred days of leaks from chilled cabinets produce 205 tonnes. Mr Best defined a carbon footprint as a company's total greenhouse gas emissions caused directly or indirectly. The purpose of assessing it was to help the firm identify, reduce and minimise emissions - and costs. But it was difficult to compare carbon footprints between companies or their activities, because they were often measured in different ways. Beware, too of carbon off-setting - paying someone else to compensate for emissions, for example by planting forests in Africa - he warned. "Many critics object to carbon off-setting in principle," he said. "Minimisation and efficiency should be the priority. In any case, some off-setting schemes may not be legitimate.