Flatulent Fauna Fables and climate

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.

See also(links updated):

Arizona Geological History Chapter 5: Jurassic Time

Ice Ages and Glacial Epochs

Research Review 3 Climate cycles and a Mammoth Mystery

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13 comments

  1. Jon asks, “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?”

    Well, maybe because nearly everything about the Earth’s environment was markedly different than today. You’d think that a geologist might be aware of that. From the University of California Museum of Paleontology:

    “As with almost any other period of the Earth’s history, the Triassic had a unique climate and biota indigenous to that time. The paleoclimate was influenced largely by tectonic events that never existed before or since.” Subsequent major transformations of Earth’s biota and oceans, leading into the Jurassic, had major impacts on the atmosphere and hence the climate. To assume or represent that present conditions are equivalent to the Jurassic would be specious if proffered by a laymen. For a geologist to do so can only be described as deceitful.

    He goes on to say, “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.”

    Here’s what communications specialist James Hrynyshyn had to say about the Smith paper Jon tries to spin:  “A paper in Nature Geoscience published early this month was much derided by the usual suspects in the pseudoskeptic community. Contrary to what many critics of “Methane emissions from extinct megafauna” claim, the research does NOT lead to the conclusion that humans are solely responsible for a global cooling event known as the Younger Dryas, which saw a brief reversal in the warming trend that brought the last ice age to an end.” Given his record here, I guess Jon qualifies as one of the ‘usual suspects’. The lead author clarifies:   “The attribution and magnitude of the Younger Dryas temperature shift, however, remain unclear. Nevertheless, our calculations suggest that decreased methane emissions caused by the extinction of the New World megafauna COULD HAVE PLAYED A ROLE in the Younger Dryas cooling event.” (my emphasis). Quite a different picture than the simplistic conclusion Jon draws.

    “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?” Well where does increased atmospheric methane come from when temperatures warm? Presently they are coming from thawing permafrosts and methane hydrates. Not such a big mystery now, is it.

    “The mammoth fart theory fails to explain previous similar abrupt cooling and warming…”

    That might be because ‘similar abrupt cooling and warming’ periods had many different forcings and feedbacks interacting in complex ways. And doing so on a world very much different than the one we know today. A geologist would know that. And one without an ideological agenda would let you know it.   JP

    By the way, the link to the Star article is broken. You can see it here:  http://azstarnet.com/news/science/flatulent-dinosaurs-helped-warm-earth-study-says/article_a6d54101-87c6-53d3-bda4-054eae47aee9.html

  2. In spite of John’s name-calling, his comment is useful because it  demonstrates several things:

    First, his statement “That might be because ‘similar abrupt cooling and warming’ periods had many different forcings and feedbacks interacting in complex ways” is finally an admission that greenhouse gases, whether carbon dioxide or methane, play a very minor role in climate change no matter what the conditions are.  But John likes to ignore the many different forcings and feedbacks when it comes to AGW contentions.

    John uses his criticism of my mention of methane emissions from dinosaurs to set up a straw man.  I do not assume conditions were the same, but John would have you believe so. I did, however, point out that current methane emissions don’t seem to have much effect.

    John’s quote from the California Museum of Paleontology is correct but a misleading buildup to his straw man.  At the beginning of the Triassic, all the continents were clumped together in an super-continent called Pangea.  By late Jurassic time, Pangea had broken up into several continents, thus allowing changes in ocean circulation patterns which had an effect on climate.

    The causes of the several Dryas cooling events are still controversial.  Among the proposed causes are change in albedo due to vegetative changes after demise of the mammoths and a change in the Atlantic thermohaline circulation, probably due to a massive influx of glacial melt water from the North American ice sheet. 

    I see that John has invoked a “communications specialist”(i.e., spinner?) to explain science to us.  I wrote that the Smith paper authors speculate about cause.  In fact they wrote: “We find that the loss of megafauna could explain 12.5% to 100% of the atmospheric decrease in methane observed at the onset of the Younger Dryas.”  John’s use of a communications specialist implies that skeptics claim the paper said change in methane was the “sole” cause of change in climate.  I did not say that, and John, your straw man is dishonest.

    Finally, in answer to my question:‘So where did the methane come from since those flatulent mammoths were no more?’ John wrote “Well where does increased atmospheric methane come from when temperatures warm? Presently they are coming from thawing permafrosts (sic) and methane hydrates. Not such a big mystery now, is it.”  Cause and effect John, again you show that greenhouse gases result from warming rather than cause it.

  3. Saying GHG’s play  “a very minor role in climate change” is like saying that the gallon of gasoline played a minor role in burning down the warehouse.

    You conflate “cause and effect” with forcing and feedback.

    You said, “Both of these papers present interesting stories, but they both fail upon close inspection.” If I set up a straw man, what did these papers “fail” to do? JP

    1. They fail to present strong evidence to support their speculation.  And you still haven’t presented any physical evidence to show that GHGs play anything but a minor role in climate change.  And, you should know that argument by analogy is invalid.

      1. Scores of commenters have presented volumes of evidence to you. You just don’t accept it. JP

      2. Oh yeah. You warned me many months ago. I only have myself to blame. (secret commie handshake) JP

      3. You’ve apparently missed a lot. Evidence doesn’t disappear because it’s inconvenient for Jonathan DuHamel. For example, I call your attention to the first couple of weeks of November, last year. One of your posts was picked up by Google News and reached a much wider than normal readership. During the following couple of weeks, hundreds of thoughtful posts presented the evidence you’ve often called for. Yes, it was ‘scores’ of people. And yes, it was ‘volumes’ of evidence. Look it up. it’s in your own archives. You may not like it. You may not accept it. But it’s there. JP

      4. The post John is referring to is When Antarctica Freezes over. You can go to the Article Index page to find it.  There were 108 comments.  None presented any credible evidence to support AGW.

      5. No, I was referring to earlier comments, particularly Nov. 9-14. No one reading those posts could fairly say that the evidence was not presented. Whether or not you “see” it is another matter.   JP

      6. I’m not sure what you are referring to.  Perhaps you should specifically state what data you think is evidence.

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