Burp vaccine cuts greenhouse gas emissions 25 September 04 Exclusive from New Scientist Print Edition. You cannot stop a sheep belching or farting, but you can make sure its eructations are less damaging to the environment. Belches and, to a far lesser degree, farts from sheep, cows and other farm animals account for around 20% of global methane emissions. The gas is a potent source of global warming because, volume for volume, it traps 23 times as much heat as the more plentiful carbon dioxide. To protect the planet from such ruminant effusions, a team led by Andre-Denis Wright of...