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Science & the Public

AAAS: Climate-friendly dining … meats

The carbon footprints of raising livestock for food

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THE FIRST OF TWO PARTS. Followup story is at: AAAS: Climate-friendly fish

For the good of the planet, we’re all being asked to reduce our carbon footprints — the quantities of greenhouse gases, aka GHGs, associated with our actions. Since some 30 percent of the global warming potential attributable to society’s GHG emissions stems from the production of foods and beverages, menu choices are critical, noted Ulf Sonesson of the Swedish Institute for Food and Biotechnology in Goteborg, today. From this climate perspective, meat eaters are the big hogs.

Sonesson was one of the speakers on a panel titled “Food for Thought” at the American Association for the Advancement of Science annual meeting. This morning’s speakers shared data from largely new analyses on how foods, production techniques, and transportation affect the climate costs associated with our dining choices. And there were some big surprises.

No longer a surprise is the relative energy intensity associated with meat, especially beef. For instance, roughly half of the GHG emissions due to human diets come from meat even though beef, pork and chicken together account for only about 14 percent of what people eat.

From a climate perspective, beef is in a class by itself. It takes a lot of energy and other natural resources to produce cattle feed, manage the animals’ manure (a major emitter of methane, a potent GHG), get the livestock to market, slaughter the animals, process and package the meat, dispose of the greater part of the carcass that won’t be human food, market the retail cuts, transport them home from the store, refrigerate them until dinner time, and then cook the beef.

Tally the GHG emissions associated with all of those activities, Sonesson says, and you’ll find it’s the global-warming equivalent to spewing 19 kilograms of carbon dioxide for every kg of beef served. Swine are more environmentally friendly. It only takes about 4.25 kg of CO2 to produce and fry each kg of pork. At the other end of the spectrum are veggies. The climate costs associated with growing, marketing, peeling and boiling up a kg of potatoes, by contrast, is just 280 grams, Sonesson reported.

Another factor contributing to cattle’s particularly egregious carbon footprint is their relative fecundity, if you will, says Nathan Pelletier of Dalhousie University in Halifax, Nova Scotia. In her lifetime, a mother fish, particularly in protected aquaculture settings, may give birth to hundreds — if not thousands — of surviving offspring. A hen could certainly produce hundreds of chicks. Even a sow can give birth to eight piggies per litter. But a cow: She tends to issue a single calf every year for maybe 10. And while she’s in gestation and then waiting to become pregnant again, farmers have to care for her and perhaps a bull — which are both big, hungry manure factories.

Many environmentalists have argued that finishing up the fattening of beef cattle on corn is worse for the environment than cattle that are raised solely on pasture grass. Pelletier says his team’s analysis finds that at least from a climate perspective, the opposite is true. “We do see significant differences in the GHG intensities [of grass vs grain finishing]. It’s roughly on the order of 50 percent higher in grass-finished systems.”

When an audience member questioned whether he had heard that right, that grass-fed cattle have a higher carbon footprint, Pelletier reiterated, “higher. Yes.” The reason: “It’s related to the much higher volumes of feed throughput and associated methane and nitrous-oxide [GHG] emissions.” He added that most pastures were highly managed, and subject to “periodic renovations and also fertilization.” Finally, with grass-fed cattle “there is also a high [grass] trampling rate. So the actual land area that you need to maintain magnifies that [GHG] difference,” Pelletier said.

But what really concerns his team about the bonus GHG emissions linked to beef is the planet’s growing numbers — and appetite for meat.

Currently, although beef accounts for only about 30 percent of the industrial world’s meat consumption, it contributes 78 percent meat’s GHG emissions there. Pork, at 38 percent of consumption, contributes only 14 percent of this meat's GHGs. Another 32 percent of the meat consumed worldwide comes from chicken, but getting these birds from farm to fork contributes only 8 percent of meat’s carbon footprint in the developed countries. By shifting some share of beef and pork production to chicken over the next four decades, the increase in meat’s GHG emissions by 2050 might be held to just 6 percent higher than today in the developed world, Pelletier said, even as the human population grows by another quarter-million each day.

Although meat's overall carbon footprint is projected to grow only a little over the next 40 years within industrialized countries, the global goal is to cut emissions in every sector. Pelletier offered some suggestions on how to do that. Some were considerably more appetizing than others.

For instance, substituting all beef production for chicken would cut meat’s projected carbon footprint by 70 percent, he said. Or perhaps per capita intake of meat could drop from a current average of 90 kilograms per year in the developed world to the 53 kg per person per year that's been advocated as sufficient for human health by the U.S. Department of Agriculture. Under this scenario, Pelletier said, “I estimate that . . . we could reduce associated [carbon] emissions by roughly 44 percent.”

Swap half of that protein now supplied by meat with soy by 2050, and “you could expect [projected] emissions to decrease on the order of 70 percent,” he said. Take the next big step — eliminating all meat in favor of soy — should drop the protein-associated carbon footprint of Western diets a whopping 96 percent.

Pelletier described that the last scenario as “utopian.” Hmmm. Not for this carnivore. I’m willing to eat chicken much of the time and reserve beef as a big treat — maybe even to be downed only in small portions. But go solely soy? That’s no utopia to me.

That said, would I consider such a sacrifice for survival of the planet? Of course — but I’m hoping someone can shoot me recipes that would made this legume taste like something other than soy. So far I only have one, but it's dynamite: for chocolate mousse pie.

Next up: What about fish?

Citations

Sonesson, U. 2009. The Secret Life (Cycle) of Foods. American Association for the Advancement of Science annual meeting, Chicago (Feb. 15).

Pelletier, N. 2009. Neither Fish Nor Fowl — Planning Dinner Around the Carbon Intensity of Protein Sources. American Association for the Advancement of Science annual meeting, Chicago (Feb. 15).
Further Reading

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