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Beware the cows.
Sure, it looks like we've got them where we want them, penned up in farms, easily led to the meat-packing plants. But in an ongoing display of passive resistance, they may be trying to take us with them.
Beyond the fat and cholesterol, they're also one of the leading sources of methane — a planet-warming greenhouse gas with 25 times the punch of carbon dioxide on a 100-year time scale. And those emissions are expected to go up planet-wide as developing countries urbanize and get richer, putting a Western-style diet within the reach of billions more people.
In the United States alone, what the Environmental Protection Agency (EPA) euphemistically calls "enteric fermentation" — the belches and farts of livestock, mostly cattle — is the second-biggest source of US methane emissions. Those emissions added up to the equivalent of 648 million metric tons of carbon dioxide in 2014. Their manure added another 60 million, according to an EPA report released last week.
And when you total up the effect of all the feed, fertilizer, and fuel involved in modern farming, that quarter-pound cheeseburger ends up having the same carbon footprint as a nearly seven-mile (11-kilometer) drive, said Dawn Undurraga, a nutritionist with the nonprofit Environmental Working Group.
"Americans eat a huge amount of meat," Undurraga said. "We eat 60 percent more than Europeans and somewhere between 150 or 200 percent of our needs."
While many consumers try to cut down on fats or carbohydrates, they often consider protein benign — "and then, we eat way too much of it and don't think about the impacts of that on the environment," she said.
Chicken is less carbon-intensive than meat. But a four-ounce serving of chicken is still comparable to driving a typical car nearly two miles, while the same serving of pork adds another mile. Eggs, yogurt, and beans can provide protein with far fewer greenhouse emissions as a result, Undurraga said.
And the numbers may be higher: A 2015 study that used satellite readings to track atmospheric methane found livestock might a bigger source of that gas, which the EPA says makes up about 10 percent of all US emissions.
Worldwide, livestock account for about 15 percent of global emissions — and reducing consumption "will be critical" to hitting the climate change targets world leaders set in Paris in December, the British think-tank Chatham House estimates. That pact set a goal of limiting climate change to 2 degrees Celsius (3.6 Fahrenheit) over pre-industrial times, a mark the world is roughly halfway toward already.
"A shift to healthier patterns of meat-eating could bring a quarter of the emissions reductions we need to keep on track for a two-degree world," Chatham House reported in November.
Eating too much meat also contributes to the rise of obesity and the spread of chronic diseases like cancer and diabetes. But worldwide consumption is expected to expand more than 75 percent by 2050 — and few people are aware of the connection between climate change and diet, Chatham House noted.
Worse yet, Undurraga said, a lot of it ends up in landfills — the No. 1 source of methane in EPA data. Food waste is the largest component of those emissions, she said, "which is crazy."
Ruminant animals like cattle have guts full of methane-producing bacteria that digest their feed, so they belch continuously, said Don Blake, an atmospheric chemist who studies methane at the University of California-Irvine. And dairies and hog farms, where animals are typically penned and their waste disposed of in lagoons, tend to produce more emissions than waste from animals that graze in open fields.
Those lagoons are "just bubbling with methane," Blake said. "If you had 1,000 pigs that you just had running in the bushes and stuff, versus 100,000 pigs on a pig farm where you washed all the manure into a lagoon, the lagoon is going to kick out a whole lot more."
Waste lagoons emit about 35 times more methane than manure that is left in the field — and the results show up clearly in satellite readings, said Alex Turner, an atmospheric chemist at Harvard University.
"There are definitely a few regions with concentrated livestock emissions," said Turner, who produced a 2015 study based on that data. Over places where waste lagoons are common, like eastern North Carolina, Iowa, and California's dairy-producing Central Valley, "We see large methane emissions," he said.
Turner's study suggested that methane emissions were underestimated, and that livestock emissions may be higher than those from the petroleum industry. But the EPA said last week that methane leaks from oil and gas also might be significantly higher than thought.
There are some signs that developing countries are trying to avoid falling into a Western-style diet as they industrialize. Brazil, one of the largest beef producers, has come out with "fantastic" dietary guidelines in recent years, and other countries are encouraging less carbon-intensive sources of protein, Undurraga said.
"I find it hard to believe we couldn't waste less and eat better and not pollute the planet as much," she said.
Follow Matt Smith on Twitter: @mattsmithatl