When Life Gives You Excrement, Make Fuel?

Via Ezra Klein, The New Scientist observes that “A kilogram of beef is responsible for more greenhouse gas emissions and other pollution than driving for 3 hours while leaving all the lights on back home.”

People tend not to understand this very well because the tendency is to use the term “carbon dioxide” as a shorthand for “greenhouse gasses.” But though CO2 is the most common greenhouse gas, it’s far from the most potent. And livestock create huge amounts of methane both from their farts (yes, really, this is a real problem) and from the decomposition of their manure. The good news, as the good people at the Danish Biogass Association were eager to explain to me yesterday, is that there’s a way to deal with the manure side of this. Methane, in addition to being terrible for the environment when released directly into the air, is also usable as fuel (“natural gas”) and when used as fuel it’s relatively clean-burning compared to coal or oil. What they do at biogas plants is basically gather up a huge stinking pile of shit which is submitted to anaerobic digestion. This leaves you with, on the one hand, some digested manure that can be used as an effective and non-emissions-producing fertilizer and on the other hand some methane gas you can use to heat homes or generate electricity.

The biogas itself involves some CO2 emissions, so this isn’t a perfectly green technology. But making the biogas is much cleaner than not making the biogas if we assume that the quantity of animal excrement produced is independent of the existence of the biogas facilities. In other words, if the demand for meat is determining the quantity of cow and pig shit, then biogas plants count as very clean. They sharply reduce the quantity of methane put into the air, and can substitute for other dirtier fuels like coal or oil. If biogas were to actually become such big business that people started raising pigs specifically for the purpose of turning their shit into home heating fuel, then that wouldn’t work ecologically at all.

Currently, though, biogas requires substantial subsidy (in the form of a feed-in tariff) to be viable. So the smart green move is to subsidize biogas production enough to clean up the excrement we have, but not so much as to encourage the creation of additional livestock. In principle, it would probably make sense to have some kind of tax on meat that could be used to raise revenue to defray the cost of biogas subsidies.