The Washington Post’s Ezra Klein, whose blog is a must-read look at the political dynamics of congressional policy-making, makes an eyebrow-raising assertion in his food column today:

Photo: CowCar

It’s not simply that meat is a contributor to global warming; it’s that it is a huge contributor. Larger, by a significant margin, than the global transportation sector.

Really? Klein cites a 2006 report by the United Nations Food and Agriculture Organization, which found that the livestock industry — the process of bringing meat from farm to table — generates 18 percent of worldwide greenhouse gas emissions "measured in CO2 equivalent."

Transportation, according to the UN report, generates 13.5 percent of global emissions measured by the same method.

And that’s an important caveat. Two gases produced in large quantities by livestock are methane and nitrous oxide, which have 23 times and 296 times the "global warming potential" of CO2. Measuring methane and nitrous oxide in "CO2 equivalent," then, pads the climate impact of livestock versus CO2 emitters such as cars and power plants.

The 2006 UN report’s comparison rings hollow in another way as well. Measuring the movement of feed to factory farms, not to mention the movement of packaged meat to supermarket shelves, means that livestock is part of the world’s transportation sector, not a separate and distinct source of emissions.

Later in his column, Klein also cites a University of Chicago study that found adopting a vegan diet would be healthier for the environment than driving a hybrid car. As Dan Lasher of the Natural Resources Defense Council discovered, however, the Chicago researchers drastically underestimated the amount of CO2 released by one gallon of gas, among other "generic calculations."

So what’s the lesson? Cutting down on burger consumption could be a positive choice that also helps the environment. But setting up false dichotomies that suggest gas-guzzlers can be mitigated by salads, that’s pretty unhealthy.