As reported last month in Nature,
Scientists have come up with new evidence in support of the controversial idea that humanity's influence on climate began not during the industrial revolution, but thousands of years ago.
Arguably, the most significant new insight emerging from this issue comes from several papers that converge on a view of pre-industrial land use that is very different from the one that has prevailed until recently. Most previous modeling simulations relied on the simplifying assumption that per-capita clearance and cultivation remained small and nearly constant during the late Holocene, but historical and archeological data now reveal much larger earlier per-capita land use than used in these models.
Why is this important? As a recent article in Science News (previewing some of the new research) puts it:
Climate scientists often select 1850 as the putative start of the industrial revolution. But the world in 1850 was not a pristine globe untouched by human hands.
Ruddiman acknowledges in his Real Climate post that debate on the early anthropocene hypothesis is far from over. Still, he writes:
the new evidence points the way toward three avenues of exploration that promise to deliver a resolution of this issue: (1) more thorough investigation of historical records of pre-industrial land use; (2) additional archeological work to fill in gaps in spatial/temporal coverage of the spread of agriculture, and (3) further modeling work to transform historical and archeological data into quantitative estimates of the effects of early agriculture on atmospheric CO2 and CH4 concentrations.
It's pretty neat that environmental history and archaeology--two disciplines of great interest to me--are being seen as increasingly important contributors to climate science debates.