The Environmental Protection Agency estimates that U.S. agriculture, including livestock production, accounts for only about 8% of total greenhouse-gas emissions in the country. Livestock in the U.S. have lower greenhouse-gas footprints than in other parts of the world. This is partly because American producers generally use higher-quality feeds, higher-yielding breeds, and more productivity-enhancing technologies such as probiotics, vaccines and growth hormones. Future improvements in feed and animal genetics could further reduce animal-agriculture’s impact. As economists have shown, one should not underestimate the ability of innovation, markets, the courts and private negotiation to resolve the adverse effects of externalities.

Moreover, the concept of externalities when applied to food is nebulous. At a recent Institute of Medicine meeting I attended, a room full of Ph.D.s struggled to understand exactly what to measure.

We would never trust a group of experts to set the price of beef, milk or automobiles. We rely on a decentralized marketplace to aggregate disparate information unknown to any single person or expert committee. And yet there is a belief among some that public-health experts can accurately divine a single true and just cost for a hamburger that will help prevent the melting of the polar ice caps and save millions of lives and billions of dollars in health-care costs.