I love milk -- the real stuff, from cows. Most Americans seem to agree, based on the fact that the average U.S. citizen consumes 1.64 pounds of dairy products every day. (That's 600 pounds a year.) Most of that milk comes from large dairy farms, where hundreds of thousands of cows burp and pass methane, a potent greenhouse gas, all day long. According to the United Nations Food and Agriculture Organization, livestock operations rival the transportation sector in their overall global warming footprint.

Figuring out how the alternatives -- goat, soy, and hemp milk, among others -- stack up is not so easy. Nobody has done a rigorous comparative analysis of the environmental impact of various "milk" products. What we do know is that methane emissions per kilogram of goat milk are higher than those of cow milk. Soybean farms often displace forests, including swaths of the Amazon rainforest, and use a lot of pesticides. By comparison, hemp requires far less water and fewer pesticides, but it's illegal to grow it in the United States. However, the vast majority of all hemp food products sold in this country come from Canada -- not quite local, but close. Hemp milk may be the best alternative (and no, drinking it will not get you high).