Silent but Deadly

All children are fascinated by farts. So are atmospheric chemists.

Farts are produced by anaerobic (without oxygen) digestion in the intestine. About 1% of flatulence is composed of malodorous, volatile sulfur gases, derived from the decomposition of protein. The proteins in meat and some vegetables (e.g., beans) are rich in sulfur-containing amino acids, and so produce stinky farts.

The average fart contains about 7% of the odorless but flammable gas known as methane—the subject of this week’s blog. Namely, rising concentrations of methane in the atmosphere are often recognized as a cause of global warming, and methane is at least 25 times more effective than carbon dioxide in effecting climate change in the atmosphere. See https://blogs.nicholas.duke.edu/citizenscientist/methane-the-other-greenhouse-gas/.

Cattle are blamed for about 1/3 of the methane that is contributed to the atmosphere from human activities, although most of the methane from cattle comes from burps, not farts. In many regions, large herds of cattle replaced the natural ruminant animals that grazed open rangelands before humans took up animal husbandry. At least one scientific analysis suggests that farting by dinosaurs may have been responsible for the warm conditions of the Mesozoic—the geologic era when dinosaurs dominated the Earth.

Humans are reported to emit about 1 liter per day of flatulent gases, about 1% of our body volume. Reports of the methane contributed by the global flatulence of humans—who does this kind of research?—suggest an emission less than about a half-a-million metric tons per year. Global human biomass is about equal to that of cattle, but methane emissions from humans are dwarfed by the contributions from grazing animals, now thought to exceed 120 million metric tons per year. If you hope to reduce your impact on the Earth’s climate, keep farting, but reduce your consumption of beef, which will reduce the emissions of methane from cattle. You may think your spouse, partner, or office mate is a major contributor to climate change, but the data say otherwise. Nevertheless, if we all eat less meat, especially beef, there would be much less methane added to Earth’s atmosphere.

Beans; what’s on your dinner plate?

References

Bar-On, Y., R. Phillips, and R. Milo. 2018. The biomass distribution on Earth. Proceedings of the National Academy of Sciences doi-org.proxy.lib.duke.edu/10.1073/pnas.1711842115

Caruso, N and D. Rabaiotti. 2017. Does it fart? The definitive field guide to animal flatulence. Hachette Books, New York.

Crutzen, P.J., I. Aselmann, and W. Seiler. 1986. Methane production by domestic animals, wild ruminants, and other herbivorous fauna, and humans. Tellus 38B: 271-284.

Dangal, S.R.S. and 5 others. 2017. Methane emissions from global livestock sector during 1890-2014. Magnitude, trends and spatiotemporal patterns. Global Change Biology 23: 4147-4161.

Kebreab, E., K. Clark, C. Wagner-Riddle, and J. France. 2006. Methane and nitrous oxide emissions from Canadian animal agriculture: A review. Canadian Journal of Animal Science 86: 135-158.

Suarez, F., J. Fume, J. Springfield, and M. Levitt. 1997. Insights into human colonic physiology obtained from the study of flatus composition. American Journal of Physiology 272: 1028-1033.

Wilkinson, D.M., E.G. Nisbet and G.D. Ruxton. 2012. Could methane produced by sauropod dinosaurs have helped drive Mesozoic climate warmth? Current Biology 22: 292-293.

Smith, F.A. and 8 others. 2016. Exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget. Proceedings of the National Academy of Sciences 113: 874-879.

2 thoughts on “Silent but Deadly

  1. I love it when science is both meaningful and fun to talk about. What a wonderfully fun way to entice fourth graders to learn chemistry.

    Happy New Year, and skip the rib roast on New Year’s Eve.

    Chris

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