Tad Friend, in his piece on Impossible Foods, a startup that makes imitation meat in the hope of solving climate change, writes, “Every four pounds of beef you eat contributes to as much global warming as flying from New York to London” (“Value Meal,” September 30th). As a professor who studies the environmental impact of livestock production, I was surprised that Friend relied on such a high per-pound emissions rate for beef, since most estimates are much lower.