Geologic History: PETM when it really got hot

The Paleocene-Eocene Thermal Maximum (PETM) was a temperature spike that happened about 55 million years ago.  The preceding Cretaceous and early Tertiary periods where hot and steamy with average global temperatures estimated to be at least 10°C (18°F) warmer than now. Atmospheric carbon dioxide was estimated to be at least three times higher than now.  Life was abundant and flourishing.  The Cretaceous has been described as both a “hot house” and as a “garden of Eden.”  There was no ice at the poles.

The PETM temperature spike caused global temperatures to get even warmer.  Drill core data from deep-sea sediments in the Atlantic and Pacific oceans suggested a rapid rise (geologically rapid, i.e., 10,000 years) of 5°C to 9°C (9-16°F) higher than the existing temperature prior to the event, that is, to as much as 34°F warmer than now.  Global temperature stayed at this elevated level for about 100,000 years, then rapidly cooled back to the prevailing normal temperature and then cooled even more.  Atmospheric carbon dioxide is estimated to have risen from the prevailing 1,000 ppm to about 1,700 ppm, more than four times higher than today.

The cause of the temperature spike is controversial.  Theories include volcanic eruption and massive forest fires that could have put large quantities of carbon dioxide into the atmosphere, changes in ocean circulation, and evolution of methane into the atmosphere.  Recent research shows that the amount of carbon dioxide in the atmosphere was insufficient to cause all of the temperature rise (Zeebe et al.), and that warming began before the rise of carbon dioxide (Secord et al.).

The current favored hypothesis is that methane (CH4) was the primary cause of temperature rise.  Methane is a powerful greenhouse gas and its evolution into the atmosphere could have initiated warming.  Carbon dioxide is formed by reaction of methane with oxygen. Under warming conditions carbon dioxide also exsolves from the ocean. Evidence suggests that warming happened in several pulses.  However, once all the methane was destroyed by reaction with oxygen, the planet cooled in spite of there being copious carbon dioxide in the atmosphere.  This shows that the weak warming effect of carbon dioxide is easily overcome by other natural forces.

Where did the methane come from? Let me set the scene. At the time of PETM, the continents were not in their present location.  The North Atlantic was just beginning to open to the Arctic Ocean; this could have changed the ocean circulation and hence the sea temperature. Volcanism and other tectonic disturbances were very active as the Atlantic opened.

There are two potential sources for methane.  One is methane hydrates sequestered in ocean sediments.  Methane hydrates are ice-like compounds of water and methane formed under cold deep sea temperatures and pressure.  Either a change in temperature or a change in pressure would release the methane.

The second, a perhaps more likely source, involves volcanism and organic methane sequestered in deep sea sediments, similar to the oil shale deposits now being explored.  As noted in Geotimes (October 2006), research in the Norwegian sea found thousands of hydrothermal vent complexes that date to the Paleocene-Eocene boundary.  As methane-bearing sediments were subducted deeper and deeper, they came into contact with hot magma from the mantle.  This can cause explosive events and rapid release of methane.  This scenario is supported by the high ratio of Carbon-12 to Carbon-13, indicating microbic generated methane, found at the PETM event.

With rapid warming came both death and opportunity.  Mammal diversity and range exploded as did that for terrestrial plants. The North American horse first appeared at this time.  At the same time, however, deep-dwelling ocean fauna suffered a rapid extinction.

Although the global temperature dropped rapidly after PETM once the methane was used up, another warming spike happened about 40 million years ago in mid-Eocene time, possibly due to a similar cause.  But afterwards another sharp cooling trend began and by 34 million years ago ice began to form in Antarctica.  Global temperatures have been dropping ever since.   We are presently in an interglacial period of an ice age that began about three million years ago.

References:

Ross Secord, Philip D. Gingerich, Kyger C. Lohmann & Kenneth G. MacLeod, 2010, Continental warming preceding the Palaeocene–Eocene thermal maximum, Nature 467,955–958.

Richard E. Zeebe, James C. Zachos & Gerald R. Dickens, 2009, Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming, Nature Geoscience 2, 576 – 580 (2009)

 

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11 comments

  1. Some interesting points here;In spite of much higher CO2 concentrations than present  during the Cretaceous and Early Tertiary (along with hotter temps),  life flourished and the planet survived.   With several times more CO2 concentration,  how is it earth’s temp did not spiral upward out of control, and instead cooled back down  and slipped  into the Pleistocene ice age?  Must have been other factors at work here.  Funny the way nature works, isn’t it?We are currently in another naturally-occuring warming cycle,  known as the Holocene Interglacial, which will continue until the Big Ice event.  Those who think they can halt 10,000 years of interglacial warming are living in self delusion.

  2. Jon–Yesterday you directed to a website that you apparently use to get some of your information. I said I would check it out and I’ve done that. The site is called ‘CO2 Science’.

    Before I address the “hundreds of articles” you say they have that show that Jim Parks, the research specialist at the Laboratory of Tree Ring Research is “out of date”; here’s just a little information about the site:
    CO2 Science is owned and run by Craig Isdo along with his father Sherwood Isdo and brother Keith Isdo.
    The has been set up as a 501c(3) which allows them to keep the sources of there funding from public view.
    Exxon/Mobil’s SEC filings show them to have been a major funder

  3. Jon–Yesterday you directed to a website that you apparently use to get some of your information. I said I would check it out and I’ve done that. The site is called ‘CO2 Science’.

    Before I address the “hundreds of articles” you say they have that show that Jim Parks, the research specialist at the Laboratory of Tree Ring Research is “out of date”; here’s just a little information about the site:
    CO2 Science is owned and run by Craig Isdo along with his father Sherwood Isdo and brother Keith Isdo.
    CO2 has been set up as a 501c(3) which allows them to keep the sources of there funding from public view.
    Exxon/Mobil’s SEC filings show them to have been a major funder.
    The Western Fuels Association, through there front group the so-called “Greening Earth Society” is another known funder, but CO2 will not be transparent about their benefactors. M The Mellon banking family, with large stock holdings in fossil fuels companies, supports CO2 through the Sarah Scaife Foundation.
    Craig Idso was formerly employed by Peabody Energy, one of the world’s largest coal companies.

    Your reader’s can make what they will of this information. Next, the review of the papers. JP

    1. Jon, For a few days I’ve been meaning to apologize for my sloppy grammar and poor proofreading. I’m working from a remote location with only my sat-linked iPad. The text entry box for comments is about the size of four postage stamps and you probably know how the iPad incessantly tries to “assist” me with spelling, which I normally do better without the help. That’s my excuse and I’m stickin’ to it. JP

      1. Jon, Regarding the papers at ‘CO2 Science’ that purport to show a quantitive temperature inrease worldwide during the so-called Medieval Warm Period. First of all there aren’t “hundreds”. I assume that was just a bit of hyperbole on your part and wasn’t meant literally. I counted 92, but in keeping with the incredible sloppiness of their work, two were published twice. I randomly chose five papers to review. This was no mean feat as they, rather than simply publishing the abstract, write their own “Description”. This forced me to access the papers myself, which they know most folks can’t do without incurring substantial costs. Of those five papers, only one reached the conclusion they said it did in the description. One actually reached the exact opposite conclusion they reported!
        In a paper concerning sediment cores from Africa’s Lake Tanginika, here is the final sentence of their description:
        This work revealed the existence of “a period of extended warmth between AD 1100 and 1400,” which clearly represents the Medieval Warm Period. And the peak LST of this period was 1.4°C cooler than the peak LST at the end of the 20th century.
        That’s right, they said “cooler”! And this is their evidence of a paper purporting to show a MWP warmer than today–world wide. I can’t imagine they ever even red the paper and I’ll show you why. Have to break here, will continue below. JP

      2. Once again my iPad “assisted” me by writing ‘red’ instead of ‘read’. Sorry.

        Here’s the last line from the Moburg 2005 paper:
        “Hence, it is not possible to determine if current temperatures have eclipsed those of a thousand years ago or whether they still fall below them; and the fairest thing to do, in our estimation, is to tentatively conclude (for this data set only) that the peak temperatures of both periods are approximately equivalent.”
        This is what ‘CO2’ says is “quantitive level 1” research showing that the MWP was warmer than today. At least this paper address the topic it is purported to by CO2.

        Check out the Hemer and Harris 2003 paper in Geology 31. It’s only five pages long. Not only does it have absolutely nothing to say about about MWP, it doesn’t refer to climate in anyway.

        Of the five papers I reviewed, three had nothing to do with addressing the MVP.

        Arseneault and Payette, 1997 and the Moburg paper are the only ones that even address the topic. Look at the dataset used by Arseneault and tell me what weight you would give to it.
        Jon, I clearly see why you are made the statements about Jim that you did. You were counting on “CO2 Science” to be a reputable source. It most assuredly is not. JP

      3. John,

        This is a reply to several of your posts:

        CO2Science has a new paper review up today which shows the MWP and LIA in Antarctica:
        http://www.co2science.org/articles/V14/N45/C3.php Therefore MWP was not confined to the northern hemisphere.

        CO2Science comments on their policy of funding here: http://www.co2science.org/subject/q/questionsaboutfunding.php And in this section comment specifically about Western Fuels Association funding:
        http://www.co2science.org/subject/questions/1999/morefunding.php

        I think the funding issue is a red herring. Or can I question funding by WWF, Sierra Club, Pew Foundation, Greenpeace etc. Why even the IPCC comes up with a rare true statement: “In climate research and modeling, we should recognize that we are dealing with a coupled non-linear chaotic system, and therefore that the prediction of a specific future climate state is not possible.” — Final chapter, Draft TAR 2000 (Third Assessment Report), IPCC.

        As to CO2Science MWP project, they say:
        “Was there a Medieval Warm Period? YES, according to data published by 1018 individual scientists from 586 research institutions in 44 different countries … and counting! This issue’s Medieval Warm Period Record comes from Victoria Lower Glacier, Ross Sea Region of Antarctica. To access the entire Medieval Warm Period Project’s database, click here.”

        Could all those scientists and institutions be co-opted by Big Oil?

        Moberg (2005) recognizes MWP and Little Ice Age even if he does not call them that. His words also show that the current warming is not unprecedented.

  4. Richard– Noone I know has ever suggested that we try to “stop 10,000 years of interglacial warming”. What would we do, stop the earth from orbiting the sun? You conveniently gloss over what Jon said about the timeframe. We are about to due in 100 years that which nature did in 10,000. To suggest that the former is equivalent to the latter is ridiculous. JP

  5. Jon, Yesterday you posted the following statement from a website you recommended to me: “Was there a Medieval Warm Period? YES, according to data published by 1018 individual scientists from 586 research institutions in 44 different countries … and counting!
    Then you asked, “Could all those scientists and institutions be co-opted by big oil?” I suppose it’s possible they could all be co-opted, but I seriously doubt it. It might be reasonable to think that a large number could be. I believe you think a large number of IPCC scientists have been co-opted. Is that right?
    Now would you answer this question for me Jon: Do you believe that the statement you quoted from the “CO2 Science” website is true? Thanks, JP

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