Separating fact from fiction on farting cows

Are the mainstream media and anti-beef activists correct in their accusations that cattle are a major contributor to climate change? Hereís a look at the facts.


By Sara Place, Ph.D., BEEF Magazine

Mar 06, 2019


Which end of the cow is responsible for most of its methane? Letís face it: anyone with a coin has a 50-50 chance of getting that right. But based on much of what Iíve read over the years, many mainstream journalists get it terribly wrong. No, itís not cattle flatulence that is the source of most of the methane gas from cattle. Itís eructation Ė or burps.


Greenhouse gases from beef cattle production have come under increased scrutiny in the past few months. A seemingly endless series of reports and articles are driving a narrative that eating less meat is a key answer to climate change. Knowing the facts is important in this debate, which isnít going away any time soon.


As the senior director for sustainability research at NCBA, a contractor for the Beef Checkoff, answering questions about greenhouse gases and cattle is part of my job. While Iím an animal scientist, not a climate scientist, I do have a unique and pertinent background in this field, conducting research where I measured methane emissions directly from cattle. It is true that cattle produce methane, a greenhouse gas 28 times more potent at trapping heat than carbon dioxide, but itís unlikely methane from U.S. cattle has been a factor in increased global average temperatures in the past few decades.


This is the core message of a new fact sheet available from the beef checkoffís sustainability research program. In the fact sheet, C. Alan Rotz, Ph.D., USDA-Agricultural Research Service, and Alexander Hristov, Ph.D., Pennsylvania State University, explain how methane from ruminant animals like cattle is a part of a natural carbon cycle that is different from methane from fossil sources like natural gas.


Cattle consume carbohydrates in plants like native grasses and corn grain. These carbohydrates contain carbon, the fundamental element of all living things, which is derived from carbon dioxide (CO2) in the atmosphere through photosynthesis.


When cattle eat carbohydrates, some of the carbon gets converted to CO2 and methane (CH4) by the rumen microbes. About once a minute, a series of rumen contractions releases this gas mixture from the animalís mouth in a process called eructation, or more simply, belching. If this natural belching process doesnít occur, cattle can suffer from bloat.


When the methane cattle release enters the atmosphere, it does have an effect of trapping heat energy. However, methane doesnít stick around very long in the atmosphere.


Over the course of a decade, the methane emitted from a cow will be transformed through a series of photochemical reactions to carbon dioxide. That carbon dioxide can then again be taken up by plants, and the cycle repeats.


Research from Oxford University demonstrates that while methane is potent at trapping heat, if the emissions from a cattle herd are steady, the concentration of methane due to that cattle herd will not increase in the atmosphere. Ultimately, this is representative of the cattle situation in the United States and makes it difficult to point to methane from U.S. cattle as a key driver in increasing methane concentrations in the atmosphere or a key contributor to warming temperatures.


Globally, the situation may be different, as based on available information from the U.N. Food and Agriculture Organization, it seems the global cattle herd has expanded. However, there are many methane sources that may explain the rising concentrations in the atmosphere, from other agricultural sources like rice cultivation to natural sources like wetlands. Another possibility is the increase in natural gas production and use (natural gas is mostly methane gas), and methane leaks from other fossil fuel production systems.


Importantly, carbon in fossil fuels is different than the carbon dioxide and methane that cattle emit, because it is not part of the natural carbon cycle. Fossil fuels are old photosynthetic carbon mostly from plants and algae from 100 to 200 million years ago.


When that carbon is released during the combustion of fossil fuels, the carbon dioxide emitted represents new carbon entering the system. Plants and the oceans have taken up some of this new carbon, but the rest has accumulated in the atmosphere; hence, the increasing concentrations of carbon dioxide we have measured since the beginning of the Industrial Revolution...