Vegetables Fight Global Warming

It turns out there's something anyone can do right now to make a big impact on global warming, says one climate researcher: Eat more veggies.

A new study of how much greenhouse gas is released into the atmosphere by the production of food shows that the difference between a meat-based and plant-based diet amounts to the same as driving an SUV versus a small sedan.

The calculations are based on data and a basic ecological concept that have been around for decades, but no one had actually done the math.

"It's just never been done," said climate researcher Gidon Eshel of the University of Chicago. "The data is simply there to mine."

Eshel and colleague Pamela Martin have published their study in the current issue of the scientific journal Earth Interactions.

The ecological concept has been taught in biology classes for decades: As energy moves up a food web — from plants to grazing animals to predators — only about 10 percent survives each step. In other words, 100 calories worth of beef patty require about 1,000 calories of grain which, in turn, require 10,000 calories of sunlight.

So if you choose to cut out the middleman (the cow) and get your 100 calories directly from the grain, you only have to grow one-tenth as much grain.

Eshel and Martin gathered U.S. food statistics, along with other data on fossil fuel use by agricultural and personal transportation. Then they looked at how much greenhouse gas was generated by the production of food.

Among the ways food generates greenhouses gases is simply by the burning of fossil fuels to power all the farming equipment, trucking and processing plants. Eshel cites the U.S. Department of Energy, which reports that food production consumes more than 10 percent of all energy use in the United States.

More specifically, 17 percent of all fossil fuels went to food production in 2002, he reported. These numbers, plus information on other agricultural greenhouse gas sources, like methane from cows and animal wastes, helped the researchers hone their numbers to something they could fairly compare to auto use.

They found that an average animal-based American diet generates about 1.6 tons more carbon dioxide per person, per year, than an all plant-based diet with the same number of calories. And that, as it turns out, is about the same greenhouse gas difference between driving a Toyota Camry and a Chevrolet Suburban, said Eshel.

"If you are interested in doing something about global warming," said Eshel, "here is an excellent example."

"There is a real issue here," agreed climate researcher David Battisti of the University of Washington. "There's a huge issue."

The amount of carbon emissions at stake in the United States alone is approximately the same as that at the center of the hotly contested federal auto fuel efficiency standards, said Battisti. Worldwide, the stakes are even higher. The people of China, for instance, are steadily shifting to an animal product diet, he points out.

"Shifting all those people to an animal protein diet will have a cost," Battisti said. In fact in most places on Earth, when people can afford it, they prefer to eat more meat, he said. But we need to study and prepare for the environmental impacts, just as we've already done for automobiles.

"Don't look at only one term in the equation," said Battisti. "You have to look at the whole impact of humans on the environment."