Posted by: ericgrimsrud | December 6, 2015

Our beloved bovines and atmospheric methane

First, some things we know about the greenhouse gases (GHG) in our atmosphere: The most abundant permanent GHG is carbon dioxide (CO2) with a background concentration of 400 ppm (parts per million).  The second most abundant is methane (CH4) with a concentration of 1.9 ppm.  Over the Industrial Era (last 160 years) CO2 has increased by 40%, from 280 ppm to 400 ppm, and CH4 has increased by 300%, from 0.60 ppm to 1.9 ppm.  The excess CO2 we add to the atmosphere will last for several centuries. The excess CH4 has a half-life of about 10 years. As a GHG, CH4 is about 25 times more effective than CO2 on a molecule-by-molecule basis.  Therefore, the 1.9 ppm CH4 presently in our atmosphere causes as much warming as would about 50 ppm of additional CO2. Since the increase in CO2 has been 120 ppm over the Industrial Age, our atmospheric CH4 causes about 40% as much warming as our excess CO2 does today. When CH4 is oxidized in the atmosphere, it is converted to CO2 and thereby adding to the CO2 total but changing that CH4 molecule to a less effective GHG.

As an upshot of the above, methane is thought to be responsible for about 30% of the GHG warming caused by all of the GHGs in our atmosphere today (the total also includes some nitrous oxide, ozone and a mix of long-lived halogenated hydrocarbons).  Because of its relatively short atmospheric lifetime, the abundance of CH4 can potentially be greatly reduced in just one decade if its emissions are significantly reduced. On the other hand, atmospheric CO2 cannot be reduced that quickly because of its extraordinarily long lifetime. Thus, there is a lot of interest today in greatly reducing the concentration of CH4 in our atmosphere in the present decade simply because, if done, this change could quickly eliminate a significant fraction, up to about 30%, of total GHG warming in the immediate future.

Next, where does atmospheric methane come from?  It is thought to come from petroleum and natural gas production (29%), bovine burps  (26%), manure (10%), landfills (18%), coal mining (10%), and a variety of other sources (8%).  Of the bovines in the USA, 71% are beef cattle, 25% are dairy cattle, 1.5 % are swine, and 2% are goats and sheep. All of these bovines are blessed with digestive systems in which the first and largest portions of their four-part stomachs, called the rumen, contains microorganisms that can reduce the cellulose in grass to smaller molecules. The gaseous methane also produced in that process is largely “burped” back out into the atmosphere.

By direct measurements it has been found that an individual midsized cow belches out about 150 kgrams of methane per year. The GHG warming of this cow’s methane emissions is roughly equal to that of driving a standard automobile from LA to NYC three times. And since there are about 100 million head of such cattle in the USA those total emissions per year are equal to that of about 300 million car trips from LA to NYC or about one such trip for each US citizen.

Putting all of the above together, it appears that about 8% of GHG warming in the USA is caused directly by our beloved bovines and about 10% if one also includes the methane emitted by bacteria action on the manure produced by those bovines.  So whether you like it or not, this is why there are a wide variety of efforts afoot today to reduce this and other sources of atmospheric methane. For a full account of those efforts directed at cattle emissions and for references to the numbers I have used in this post, see . In that report you will see that while much improvement is being made in the management of bovine manure only limited success has been achieved, to date, in reducing their direct methane emissions.

As a result of the above information, I am now very pleased that my beloved pet (a black lab named Bek) has only one relatively standard stomach. While it used to annoy us when he puked up the grass he had tried to eat, it no longer does. It does appear, however, that in the immediate future, we might be increasingly encouraged to avoid foods, both dairy and beef, that come to us via Bek’s friends in the ruminant family. We will surely retain some of these beloved mammals for the variety of other valued functions they serve, but to mass-produce them as food sources now seems to make no more sense than using fossil fuels for energy production.  My spouse, Kathy, is an excellent cook and in recent years we have enjoyed many fine meals made from ingredients that did not require the participation of bovines. Thus, a significant reduction in bovine-related foods could provide a desperately needed reduction greenhouse gas warming in the present decade.


  1. Well stated Eric.
    With an alarmingly explosive human population growth and unfortunately a taste for an animal-based, Western-style diet has wreaked havoc on public health (chronic disease), deforestation, desertification, land and water (including ocean)contamination. Intensive animal agriculture is highly unsustainable because of the ratio and lack of arable land and water resources.
    The late Dr. Robert Goodland..former executive of environmental concerns of The World Bank has this urgent message to share with us.


  2. Good post. I don’t know if you have seen the following article (somewhat related) on rice paddy methane:
    It claims 10% of methane comes from growing rice. Also claims that Genetically engineered rice cuts emissions to close to zero.

    [Thanks for the additional reference, Owen. It provides some interesting info concerning the emissions by agriculture, in general and, as you mentioned, describes a genetic solution to methane emissions associated with rice production – a process that feeds half of the world’s population. Apparently this problem can be solved. We have little indications yet that the one associated with bovines can be ]

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