STATS ARTICLES 2010
Are cows burping up a greenhouse gas storm?
Rebecca Goldin Ph.D and Cindy Merrick, November 5, 2010
How to digest the findings on bovine wind and potential cures
A few weeks ago, Penn State researcher Alexander Hristov announced a dietary breakthrough in the effort to reduce methane emissions of ruminant livestock. Methane is a potent greenhouse gas which, while present in our atmosphere in smaller quantities than CO2, has more than 20 times CO2’s global warming potential. In his experiment on dairy cows, Hristov found he could reduce the amount of methane produced in the cows’ rumen (a portion of the stomach which is peculiar to grazing animals such as cows, goats and sheep) by using an oregano-based food additive. The additive appears to reduce dairy cows’ methane emissions by about 40 percent, with the bonus of increasing milk production by the not insubstantial amount of three pounds per day. Similar results have been announced elsewhere: In July, Newcastle University announced that curry spices had a similar effect to oregano. “Any cut in methane emissions would be beneficial,” says Hristov of the findings.
It is when one asks the obvious follow-up – “just how beneficial?” – that one enters the murkier world of statistics and counter-statistics, pointed debates over methodologies of measurement, and a code lexicon of acronyms like GWP, TgCO2Eq, and LULUCF.
In attempting to quantify emissions, scientists and climate change experts found that simple scientific units of quantity don’t give an adequate picture. Raw quantities are less meaningful, because there are many greenhouse gases with widely varying chemical properties. Methane, for example, is 21 times more effective at trapping heat in the atmosphere than carbon dioxide, when compared over a 100-year period. Thus a unit of measurement, devised by the International Panel on Climate Change (IPCC) and used globally, known by the acronym “TgCO2Eq,” takes into account the measured “Global Warming Potential” (GWP) of a greenhouse gas and expresses amounts of it in terms of teragrams (Tg = 1 million metric tons) of carbon dioxide equivalent (CO2Eq). Other measures of regional and global emissions exist, such as ones that take into account further environmental impacts of creating greenhouse gases, such as deforestation and negative or positive land-use changes, such as erosion or replanting of trees.
The Politics of Method
Answering the “how beneficial” question with regards to reducing cow emissions presupposes good measurements of the climate impact of livestock. In a 2006 report titled “Livestock’s Long Shadow,” the United Nations’ Food and Agriculture Organization (FAO) ascribes to the global livestock sector fully 18 percent of the world’s human-caused (anthropogenic) greenhouse gases. As they bluntly state, “this is a higher share than transport.”
The UN’s measurement is what is termed a “Life Cycle Assessment” (LCA) measurement, part of the global International Organization of Standards’ IS0 14040. As described by the US EPA, “LCA enables the estimation of the cumulative environmental impacts resulting from all stages in the product life cycle, often including impacts not considered in more traditional analyses.” Thus, in addition to the direct emissions – cow burps – the LCA also figured in is the gas that fueled the tractor that fertilized the field that grew the corn that fed the cow. In fact, the UN report says, the largest share of greenhouse emissions from the agriculture sector is due to a factor labeled “land-use, land-use changes, and forestry” (LULUCF), in which deforestation plays a major role. This seems to rather sideline the cow-burp issue.
However, formidable objections have been raised to the UN’s estimate – not because the measurement is incorrect – but because its comparison to the emissions from the global transportation sector is misleading. A voice of opposition, Frank M. Mitloehner from UC Davis, in a 2009 report “Clearing the Air: Livestock’s Contribution to Climate Change,” points out that the UN “attempts a life cycle assessment for global livestock production but does not use an equally holistic approach for its transportation prediction numbers.” An official from the UN’s Food and Agriculture Organization confirmed this in an interview with the BBC: “I must say honestly that he [Mitloehner] has a point – we factored in everything for meat emissions, and we didn’t do the same thing with transport.”
Whatever a true global comparison between the agriculture and transportation sectors may tell us, according to EPA data for the United States the transportation sector is responsible for 27 percent of our greenhouse gas emissions, while agriculture contributes only 6 percent (though other sources suggest the number is 9 percent). Of this amount, about 26 percent is attributed to enteric fermentation. Depending on the estimate, this amounts to 1.6-2.3 percent of total greenhouse gas emissions. More than anything else, this makes one wonder about the value of a global number, when factors like infrastructure, farming techniques and availability of modern efficiencies and new research (such as Hristov’s) vary so widely from country to country.
More Useful Comparisons
So, how do we digest Hristov’s breakthrough if it works as advertised? If only 2 percent of greenhouse emissions are attributable to bovine gas, do we care about reducing cow-burped-methane by 40 percent? In fact, here are some numbers that tell us why we should. The United States, the world’s largest source of CO2 and other gases associated with climate change: in 2008 it emitted about 1,500 Tg CO2Eq more greenhouse gases than the second-largest producer (the 27 countries of the European Union measured together). The total U.S. emissions is about 6,900 TgCO2Eq. The difference between the United States and the European Union is comparable to the total emissions of Europe’s biggest polluters – the U.K. and Germany – put together.
The 2 percent of emissions attributed to cow burping is about 138 TgCO2Eq. A 40 percent reduction in these gases translates to 55.2 TgCO2Eq less greenhouse gas emitted into the atmosphere According to the data submitted by each nation member of the UN’s Climate Change Convention, this amount of greenhouse gas is comparable to the amount produced in 2008 by Switzerland, and about twice the emissions of Norway that year. Our cows, (and to a lesser extent our sheep and goats) are out-performing whole nations in the direction of climate change. So, yes, our burps matter.