Cody Sheehy is a rangeland ecologist and independent documentary producer.

By Cody Sheehy

A couple of months ago, nearly lost amid the “Hopenhagen” hype,  the University of California, Davis (UCD) put out a press release with an admonition: “Don’t Blame Cows for Climate Change.” The release was a first look at some work conducted by UCD Associate Professor and Air Quality Specialist Frank Mitloehner. His study examines the greenhouse gases, or GHGs, emitted by the livestock sector.  As California’s air regulators turn more attention toward methane in particular, the report remains timely.

Mitloehner’s paper is entitled: “Clearing the Air: Livestock’s Contributions to Climate Change,” and was published in the peer-reviewed journal Advances in Agronomy. The paper is a synthesis of current science on the cattle-climate connection. Mitloehner has been updating some of that science in recent years.

In 2008, I stopped by his cluster of “bio bubbles;” airtight domes that serve as high-tech stables for cows. Inside, Mitloehner had set up simulated dairy operations, measuring GHGs emitted by the cows’ digestive process and decomposition of the manure. The numbers then in common use had been generated in the 1930s.

Mitloehner says cattle gets a bum rap in the media, and points to some examples, including a 2007 story in Time magazine, which included assertions like: “Which is responsible for more global warming: your BMW or your Big Mac? Believe it or not, it’s your Big Mac,” and “A 16-oz T-bone is like a hummer on a plate . . ”

In many cases, Mitloehner says the statements are crafted from an influnencial 2006 United Nations report entitled: “Livestock’s Long Shadow.”  According to the executive summary, “The livestock sector is a major player, responsible for 18 percent of greenhouse gas emissions measured in CO2 equivalent. This is a higher share than transport.”

But Mitloehner points to a quote deeper in the report:

“The respiration of livestock makes up only a very small part of the net release of carbon that can be attributed to the livestock sector. Much more is released indirectly by other channels, including: the burning of fossil fuel to produce mineral fertilizers used in feed production, methane release from the breakdown of fertilizers and from animal manure, land-use changes for feed production and for grazing, land degradation, fossil fuel use during feed and animal production and fossil fuel use in production and transport of processed and refrigerated animal products.”

Mitloehner cautions that the transportation number they use only accounts for tailpipe emissions. To be even-handed, he says, the authors should’ve incorporated emissions from the entire oil industry, including refinement of the oil and production of cars. In the UCD release, Mitloehner calls it a “lopsided ‘analysis” and “a classical apples-and-oranges analogy that truly confused the issue.”

Meanwhile, the Bio-bubbles have been generating some interesting numbers. Mitloehner found that the amount of methane the cows respire (belch) and how much is released in the breakdown of animal manure is quite different from what previous research had calculated. In combination, these two sources represent the most direct GHGs from the livestock industry, even if they’re not the largest GHG emitter associated with the industry. They’re also the most out of date.

Emission factors used in “Livestock’s Long Shadow” provide an estimate of methane respiration of about 86 million tonnes (metric tons) of methane (CH4) and 17.5 million tonnes of CH4 annually from manure decomposition. In the annex of the UN report, the authors write: “Obviously, great improvements to the estimates of emission factors could be made if more data on nutrition and production were available.” And so it is that inside his bio-bubbles, Mitloehner has come up with numbers much lower than those that represented the conventional wisdom since 1938.

All in all, we’ve got a discussion about comparing apples and oranges (more appealing than manure, granted) and some updated numbers that lower the emissions of livestock in one category. As with any scientific paper, there will probably be debate on both of these points and new ones, but let’s look at the broader consequences. Will industry look at this study and see an incentive to update and revise carbon emission numbers all across the board?

According to Emilo Laca, an agricultural ecologist at U. C. Davis, some of these questions will be fodder for policy debates that lie outside the realm of science. He says “The real question is, ‘How are we going to split this up?’” Laca used a hypothetical problem to explain: Let’s say that a certain livestock industry consumed 30% of soybean production as a food source. Livestock producers might concede that they should be accountable for 30% of carbon emissions related to soybeans. It makes sense. It’s what the numbers say. Others might counter that without this certain livestock industry, the soybean market would behave differently and some amount–lets guess 70%–wouldn’t need to be planted. Therefore, the livestock industry in this example is responsible for 70% of the emissions, not 30%. Science can support both interpretations. As Laca says, the decision is how to “split” things up. And ultimately, those decisions may fall to policy wonks.