Time Magazine: Big, bad carbon dioxide gets most of the attention when it comes to greenhouse gases, but it’s not the only one that’s warming the earth. Methane — a gas that is found in everything from landfills to cow stomachs — also plays a big role. Although global methane-emissions levels are much lower than CO2 emissions, pound for pound methane is a more powerful greenhouse gas; a ton of it has 23 times the warming effect of a ton of CO2. And methane, like CO2, is on the rise thanks to us: about …