How Our Diet Impacts the Earth

Meat eaters like Tim don't want to admit it, but they have a significantly bigger impact on global warming than vegetarians. The United Nations says so. Stonyfield Farms, a big eastern U.S. dairy, says so. And lots of scientists are now looking at ways to reduce the effect that livestock has on the planet.

This is a touchy, touchy issue. Our doctor is a yoga-advocating, exercise-promoting, good-eating health nut. But don't talk to him about meat. He doesn't believe that a big piece of seared red meat slows you down, let alone that it has an outsized effect on the planet's health. 

Here's the first half of the problem: Not only is raising livestock energy intensive, because half of all grain grown in the U.S. goes not into cereal but into cows — to fatten them up. Those grains require a lot of herbicides, pesticides, and fertilizers — all energy intensive. Then the meat and dairy has to be trucked to the butcher/processor, and then trucked to warehouse, and then trucked to the store. 

"Stop eating animals," says Mike Tidwell in the February issue of Audubon magazine, "and you use dramatically less fossil fuels." As much as 250 gallons less oil per year for vegans, says Cornell University’s David Pimentel, and 160 gallons less for egg-and-cheese-eating vegetarians.

Tidwell, who grew up in Tennessee on Memphis barbeque, says he loves to eat meat. But he says that changing light bulbs and driving a Prius probably don't do as much for the planet as changing your diet. But nobody wants to talk about it, because 97 percent of Americans love to eat meat. This ain't a popular notion.

Here's the second half of the problem: Cows belch.

Livestock used to eat what they always ate — grass. But government subsidies after World War II made corn and soy cheap and plentiful, so farmers began feeding it to their cows. But corn and soy have a different fatty acid structure, and now cows do what people do when they have a dramatic change to their diet: burp and fart. 

"Ruminants — cows and sheep — generate a powerful greenhouse gas through their normal digestive processes (think burping and emissions at the other end)," Tidwell writes. "What comes out is methane (23 times more powerful at trapping heat than CO2) and nitrous oxide (296 times more powerful).

Frank Mitloehner, a University of California, Davis, professor who places cows in air-tight tent enclosures and measures what he calls their “eruptions,” says the average cow expels — through burps mostly, but some flatulence — 200 to 400 pounds of methane a year.

"Indeed, accounting for all factors, livestock production worldwide is responsible for a whopping 18 percent of the world’s total greenhouse gases, reports the U.N. Food and Agriculture Organization. That’s more than the emissions of all the world’s cars, buses, planes, and trains combined."

Now livestock farmers and dairy producers are trying to do something about it. 

Nancy Hirshberg, Stonyfield’s vice president for natural resources, commissioned a full assessment of her company’s impact on climate change in 1999 that extended to emissions by some of its suppliers.

“I was shocked when I got the report,” Ms. Hirshberg said, “because it said our No. 1 impact is milk production. Not burning fossil fuels for transportation or packaging, but milk production. We were floored.”

From that moment on, Ms. Hirshberg began looking for a way to have the cows emit less methane, according to an article in the June 4, 2009 New York Times.

Since January, cows at 15 farms across Vermont have had their grain feed adjusted to include more plants like alfalfa and flaxseed — substances that, unlike corn or soy, mimic the spring grasses that the animals evolved long ago to eat.

At one of the farms in the Stonyfield study, the methane output of Guy Choiniere’s herd in Highgate, Vermont, had dropped 18 percent. Meanwhile, milk production has held its own.

And there's a side benefit. “They are healthier,” he said of his cows. “Their coats are shinier, and the breath is sweet.”