A story making the rounds is creating headlines such as the one in the ever credulous Arizona Daily Star: “Flatulent dinosaurs helped warm Earth, study says.” British researchers posit that the flatulence of herbivorous dinosaurs produced so much methane that it warmed the climate. The paper, published in Current Biology is summarized by the authors as follows:
Mesozoic sauropods, like many modern herbivores, are likely to have hosted microbial methanogenic symbionts for the fermentative digestion of their plant food. Today methane from livestock is a significant component of the global methane budget. Sauropod methane emission would probably also have been considerable. Here, we use a simple quantitative approach to estimate the magnitude of such methane production and show that the production of the greenhouse gas methane by sauropods could have been an important factor in warm Mesozoic climates.
If you read the story (full text here) you will find that the contention depends on many assumptions and rather extravagant extrapolation. The gassiest dinosaurs were the Sauropods which became abundant during the Jurassic Period about 150 million years ago. Global temperatures are estimated to have been 18 F warmer than today, but that warmth began in the preceding Triassic Period about 250 million years ago. There seems to be a timing problem. Also, the researchers estimate that the amount of methane produced by dinosaurs was similar to the amount produced today by livestock farming and industry, so why aren’t we warmer?
At the end of the paper, the researchers note as an attempted justification for their speculation:
“Although dinosaurs are unique in the large body sizes they achieved, there may have been other occasions in the past where animal-produced methane contributed substantially to global environmental gas composition: for example, it has been speculated that the extinction of megafauna coincident with human colonization of the Americas may be related to a reduction of atmospheric methane levels.”
That references a 2010 paper in which the researchers estimated the amount of methane produced by mammoths and other large herbivores. They speculate that the arrival of humans in North America and the subsequent disappearance of these animals reduced methane emissions and led to an abrupt cooling period, the Younger Dryas, about 12,800 years ago.
At the end of the Younger Dryas, the global temperatures and atmospheric methane both rose rapidly. So where did the methane come from since those flatulent mammoths were no more? The mammoth fart theory fails to explain previous similar abrupt cooling and warming in the Older Dryas period and the Oldest Dryas period, nor a subsequent similar event about 8,200 years ago.
Both of these papers present interesting stories, but they both fail upon close inspection. Still, science is speculative and the stories make headlines and get the authors published.
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