Return of the Early Anthropocene?

Most if not all readers of blogs like this one are at least passingly familiar with the concept of the Anthropocene, coined by Paul Crutzen – the idea that human impacts across the planet are so widespread as to constitute a new geological epoch of the same name. Most are also probably familiar with Bill Ruddiman’s “Early Anthropocene” hypothesis (RealClimate did a brief rundown a few years ago, and John Mashey has used it over at Deltoid as an illustration of the scientific process “in action”), which Ruddiman believes began some 8,000 years ago due to widespread deforestation and subsequent rice cultivation.

Images courtesy of Flickr users Okinawa Soba (above) and cuellar (below) used under Creative Commons

Ruddiman’s Early Anthropocene recently made an appearance at the Fall 2008 AGU conference – in a presentation by Vavrus, Kutzbach & Philippon (after Vavrus’ presentation Climate Model Tests of the Early Anthropogenic Hypothesis (Vavrus, Ruddiman & Kutzbach 2008)).Vavrus’ group claims that their findings support the controversial idea that early anthropogenic perturbation of the carbon cycle may have prevented an impending/overdue glaciation (Wally Broecker is an especially vocal critic of this notion, pointing out seemingly opposing oceanic and orbital paleo evidence that indicate a natural source for the CO2 rise as well as a lengthy interglacial; also here and here).

Also at the AGU conference, a different group expanded on one aspect of Ruddiman’s hypothesis (pandemics = lower CO2 due to a reduction in biomass burning + reforestation), finding widespread deaths among indigenous groups due to pandemics spread by the European “Conquest” of the Americas dramatically reduced CO2 levels, acting as a “first-order” contributor to the so-called Little Ice Age.

It will be interesting to see if these prove to be supporting “bricks”  (to borrow John Mashey’s phrasing) for the Early Anthropocene hypothesis, or whether they will be “kicked away” by future studies. In either case, at least for now, Ruddiman’s idea seems to have plenty of life in it yet.

[UPDATE: It seems I’m not the only one with Ruddiman on the brain of late…]

5 responses to “Return of the Early Anthropocene?

  1. Thanks for the interesting pointers. I found Ruddiman thanks to Mashey. This provides a wonderful opportunity to watch real science evolve before our eyes.

    Paul

  2. 1) There are of course 3 hypotheses, 2 of which are related (early CO2 & CH4). See especially the two key charts on page 5 of Vavrus presentation mentioned by ThingsBreak. I.e., the red lines are the Holocene CH4 and CO2, compared to earlier stages.

    Also, see the chart C on page 6: this is from a recent archaeology paper by Li et al on the growth of Chinese rice acreage. There’s also Early rice farming and anomalous methane trends. (subs rqd)

    The big Chines ricegrowth spurt ~coincides with the CH4 trend reversal on page 5. Of course, correlation is not causation, but this is fascinating timing.

    2)For the third hypothesis:
    I think the “New archeological discoveries revealing extensive networks of geoglyphs and urban polities in Pre-Columbian Amazonia suggest that our estimates of reforestation, and consequent effects on atmospheric CO2, may be conservative. ” comment refers to work like “Ancient Earthmovers of the Amazon”
    Charles C. Mann, in August Science (subs rqd):

    “The forested western Amazon was once thought barren of complex human culture. But researchers are now uncovering enigmatic earthworks left by large, organized societies that once lived and farmed here.”

    3) A Broecker/Ruddiman debate, with the current data in hand, would be quite interesting. The Broecker EOS piece mentioned above was ~3 years ago. Ruddiman had this in Reviews of Geophysics about a year ago.

    At some point, I may put together a timeline illustrating the tos-and-fros: as Paul says, a wonderful opportunity, especially as it’s a *real* science controversy taht is much more accessible than many to us laypeople!

  3. Great summary. Broecker makes clear how complicated this gets — because at the slow rate of change in past events the ocean has a chance to be fully involved, and over those long time spans orbital forcings also change.

    It’s helpful as a reminder how incredibly fast the Anthropocene change is happening in the atmosphere — so fast it can’t propagate through the rest of the biogeochemical cycle as before.

    Broecker:
    “… Both fragmentation and shell
    weight indices of CaCO3 dissolution show an
    early Holocene preservation maximum followed
    by a pronounced increase in the extent
    of dissolution [Broecker et al., 2001].
    But, as Ruddiman’s scenario also calls for
    a preservation event, this result does not allow
    the two scenarios to be distinguished. It does,
    however, rule against explanations involving a
    weakening of the ocean’s biological pump or
    a warming of the sea surface.
    Ruddiman’s reply to this would surely be,
    But what about the previous interglacials?
    Why do they not show a rise in atmospheric
    CO2 content as a result of calcium carbonate
    compensation? The explanation likely lies in
    the current small magnitude of the eccentricity
    of the Earth’s orbit compared with that during
    the previous three interglacials….”

  4. For anyone in the vicinity, Ruddiman is presenting as part of the U of Toronto “Center for Global Change Science” Distinguished Lecturer series on Feb. 10. “Pre-industrial Agriculture Prevented Present-Day Glaciation”

    http://www.cgcs.utoronto.ca/Seminars.htm

    The whole series has been great.

  5. Pingback: Return of the Early Anthropocene? « The Way Things Break | UNDERSTOREY

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s