Cows may look pretty benign as they languidly chew on grass in farm fields, but some environmentalists warn that the animals’ farting, belching and pooping is a major contributor to climate change. A 2006 United Nations report estimated that cows, along with other livestock like sheep and goats, contribute about 18 percent of the greenhouse gases that are warming the planet — more than cars, planes and all other forms of transportation put together [source: Lean]. That’s largely true because bovine emissions are rich in methane, a gas that’s 21 times more efficient than carbon dioxide at trapping heat in the atmosphere [source: Los Angeles Times].

Here’s how we can harness the power of methane emissions from cows as a form of alternative energy…