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Pushing back the Anthropocene at the AGU

Thursday, December 25, 2008

The Early Anthropocene Hypothesis holds that human alteration of climate began with forest clearing and rice production more than 6 thousand years ago.  Here are my personal impressions of recent work supporting this hypothesis, from last week's annual meeting of the American Geophysical Union (AGU) in San Francisco (a conference of 15,000- so big its like Woodstock for Earth scientists).

It all started Monday morning (12/14) when I presented my poster on global changes in the biosphere converting biomes to anthromes during the Industrial Revolution ("Anthropogenic Transformation of the Biomes, 1700 to 2000"; collaborative work with Kees Klein GoldewijkStefan Siebert and Navin Ramankutty.  My student, Jonathan Dandois, was also there presenting a poster, and so was Kees, presenting his work on trends in land use and population during the entire Holocene (provocatively entitled: Anthropocene Holocene?)  I soon ran into Jan Zalasiewicz - whose poster next to mine described his work dating the Anthropocene to the beginning of the Industrial Revolution- and Mark Williams as well.

But things really started cooking when Bill Ruddiman, originator of the Early Anthropocene Hypothesis, arrived unexpectedly and jumped right into a discussion of prehistoric populations, land use and climate change!  This led to a really fun lunch with Bill, Kees, Jonathan and I, where Bill laid out the most recent evidence and revisions of his hypothesis- a prelude of what he and others would present later and a very exciting lesson on climatology and long-term climate dynamics.

The next day, we held an oral session, Earth System Science for the Anthropocene, together with Jan and Alan Haywood, with great speakers, including Jon Foley and Pam Matson, followed by another great lunch and discussion with the speakers and hosts at my favorite dim sum place in San Francisco.  At the session Jan got lots of interest about his new book, "The Earth After Us: What Legacy Will Humans Leave in the Rocks", from a Wired reporter, leading to a live Wired event that evening (I've just purchased up a copy - should be a fascinating read.

Finally, there was Bill Ruddiman's session, which included talks describing new results investigating early human impacts on global climate by a variety of climate scientists, including work using couple climate/biosphere models  and ice core records.  Most of the work was strongly in support of the hypothesis that natural climate forces similar to those of prior interglacial periods cannot explain the sustained warming trends observed during our current interglacial period (the Holocene), and that the release of methane and carbon dioxide caused by land clearing and paddy rice, together with ocean feedbacks on these climate forcings, are the best supported explanation for observed climate and greenhouse gas trends during the Holocene.   Overall, it appears that prehistoric agriculture likely caused at least 1/3 of the total global warming that humans have caused.

By the end of Bill's session, it really did feel like a scientific revolution had occurred- that the weight of evidence had shifted to those supporting his Early Anthropocene Hypothesis.  I would bet that in the future we will look back on this session as a turning point for our perception of humans in nature: we have been major drivers of climate change ever since we began deforesting and farming, even before the Industrial Revolution.  So it sounds like Kees is right- Holocene may really = Anthropocene!

Here's my video blog post about this: http://www.youtube.com/watch?v=6lX06bZNk8E


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