Dear Editor,

I read with interest the article in the June 2017 Render by [Dr.] Frank Mitloehner, professor at the University of California, Davis, about “Livestock’s Contribution to Climate Change.” There is one aspect of this topic I was looking for in the article that was never mentioned. Cows, pigs, chickens, and human beings are all “biomass.” Everything we eat and discharge in any way contains biogenic carbon, not fossil carbon.

The reason that GHGs [greenhouse gases] (particularly carbon dioxide) are growing in concentration in our atmosphere is because we are digging up, or pumping up, fossil-based carbon fuels and burning them. In contrast, the amount and complexity of life forms on planet Earth, on land, in the oceans, plants, and animals are all part of the natural carbon cycle. If we were not digging up and burning fossil-based carbon, there would be no net increase of carbon (dioxide) in our atmosphere.

Now people can argue that we use fossil fuels to run tractors and agricultural machinery to grow crops and feed cattle and pigs and chickens. So, from an “accounting” point of view, those fossil-based fuels used in agriculture can be transferred to the cows and pigs and chickens that are being supported. But, those fossil fuels could eventually be replaced with renewable fuels. Then, would the natural emissions from animals still be considered GHGs? We could cut trees to use as fuel to burn and generate electricity (and carbon dioxide). If we did this “sustainably” and cut only two or three percent of a forest in a given year to run the electrical power plant, and re-plant the harvested two or three percent, the designated forest could generate electricity forever, with no net carbon emissions, since the other 97 to 98 percent of the forest would continue to grow and re-absorb carbon dioxide from the atmosphere via photosynthesis every year.

So, I don’t think that natural emissions from cows, or other animals, should even be considered in the GHG mass balance equation. This is biomass-based biogenic carbon, not fossil carbon. If methane gas from a (fossil-based) natural gas well is leaking gas to the atmosphere, yes, that is contributing to the overall GHG mass balance. But methane from a cow’s stomachs is all biogenic carbon; it should not be added to the GHG mass balance as it is part of the natural carbon cycle. The carbon dioxide that we all exhale every day, along with every other person and critter on this planet, is not contributing to GHGs, but if we dig up coal and burn it, that resulting carbon dioxide is contributing to the GHG mass balance. “Carbon dioxide” and “carbon dioxide” appears to be the same, but it isn’t. It depends upon the source of the carbon – is it biogenic-based carbon or fossil-based carbon? That is the question!

So, I disagree with the author’s conclusion – “Livestock accounts for only 4.2 percent of all GHG emissions in the United States.” On the contrary, livestock contribute zero percent GHGs to our atmosphere.

Kirk Cobb
Senior Process Design Engineer
Superior Process Technologies
Minneapolis, Minnesota

Render offered Dr. Mitloehner the opportunity to respond:

Kirk Cobb has made some valid points and some that require clarification.

It is correct that carbon dioxide (CO2) from livestock respiration is not counted in any of the serious lifecycle assessments. The reason is that the forage that livestock consumes assimilates atmospheric CO2 and releases oxygen. Once the animals eat these feedstuffs, they metabolize the nutrients and expel CO2 – a wash overall.

CO2 emissions are not a major consideration from animal agriculture but the much more heat trapping gases methane and nitrous oxide are. Methane is 25 times and nitrous oxide almost 300 times more potent than CO2 and livestock production is one of the major emitters of both. In the emission inventories, they are converted into CO2 equivalents.

Cobb maybe half jokingly refers to cow farts as not being the issue and he is right. It is not the back end but rather the front end of ruminants that are a main methane source. The animals consume carbonaceous feed and then microbes make some of that into the potent methane or even into nitrous oxide. This conversion of nutrients into belched- or manure-derived methane or that of fertilizers into nitrous oxide is what makes up the majority of the impacts the livestock sector has on greenhouse gases.

The time has come to own the sector’s environmental responsibilities and continue the path of making further improvements that are called for by today’s society and the marketplace.

Frank Mitloehner
Davis, California

August 2017 RENDER | back