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...]