Ruddiman’s (2003:265–268) argument for an early start date for the Anthropocene is based on the detection of anomalous CO2 levels beginning about 8000 years ago, which increased steadily in value through the Late selleck chemicals Holocene to about 2000 BP. He argued that this distinctive rise in greenhouse gases may have been the product of ancient land clearance practices associated with early agrarian production. More recently, Dull et al. (2010) presented convincing paleoenvironmental

and archeological data sets to argue for extensive anthropogenic burning in the Neotropics of the Americas in the Late Holocene, which they believe must have greatly increased SRT1720 ic50 CO2 concentrations in the atmosphere. They contended that early colonial

encounters beginning about A.D. 1500, which brought disease, accelerated violence and death to the Neotropics, lead to a marked decrease in indigenous burning. This significant transformation in the regional fire regime, coupled with the reforestation of once cleared lands, reversed the amount of CO2 and other gases being emitted into the atmosphere. It is possible, as articulated by Dull and others, that these changes in greenhouse gas emissions may have amplified the cooling conditions of the Little Ice Age from AD 1500–1800. We believe that estimates for anthropogenic carbon emissions described by Ruddiman (2003:277–279) and Dull et al. (2010) may, in fact, be underestimating the degree

to which CO2 and other greenhouse gases were being introduced into the atmosphere in Late Holocene times. Both studies, by focusing primarily on anthropogenic burning by native farmers, do not fully consider the degree to which hunter-gatherers and other low level food producers were involved in prescribed burning, landscape management practices, and the discharge of greenhouse gases, as exemplified by recent research on the Pacific Coast of North America. For example, recent studies along the central coast of California have identified fire regimes in the else Late Holocene with “fire return intervals” at a frequency considerably greater than that expected from natural ignitions alone (Greenlee and Langenheim, 1990, Keeley, 2002 and Stephens and Fry, 2005). These findings support a recent synthesis for the state that estimates that six to 16 percent of California (excluding the southern deserts) was annually burned in prehistoric times, an area calculated to be somewhere between two million to five million hectares. The annual burns are argued to have produced emissions at levels high enough to produce smoky or hazy conditions in the summer and fall months in some areas of the state (i.e., Great Central Valley), not unlike what we experience today (Stephens et al., 2007).