Two proposed natural causes for an observed increase in CO2 around 8000 years ago (natural loss of terrestrial biomass and changes in ocean carbonate chemistry) are considered and rejected. Instead, the rise in CO2

is attributed to the widespread initial pre-industrial forest clearance in Eurasia associated with the expansion of agricultural landscapes (Ruddiman, 2003). This increase in CO2 is characterized as being “imperceptibly gradual, and partially masked by a larger cooling trend” (2003, p. 285). The supporting evidence offered for deforestation associated with agriculture being the cause of the observed CO2 rise at ca. 8000 B.P. is also admittedly limited: “these estimates of land clearance and carbon emissions are obviously just rough first approximations” (2003, p. 277), consisting of general observations regarding the MI-773 purchase initial expansion of agricultural societies out of the Near East into Europe and their subsequent intensification,

as well as similar but less well documented trends in China and India. Like Certini and Scalenghe, ecologists Christopher Doughty, Adam Wolf, and Christopher B. Field (2010) use a pedospheric buy SP600125 indicator to mark the beginning of the Anthropocene, but focus on a much smaller, regional scale of proposed human impact. Their proposed marker for the onset of the Anthropocene is a large increase in Birch (Betula) pollen from Alaska and the Yukon during a narrow 1000 year period at ∼13,800 B.P. They suggest that this increase in Betula modified the land surface

albedo (i.e. reduced reflectivity), resulting in a projected regional warming of up to 1 °C. Given the general temporal correlation between this documented increase in Betula and the extinction of mammoths, they hypothesize that reduced herbivory associated with the disappearance of megafauna played a causal role in the expansion of birch forests and the resultant rise in regional temperature levels. The extinction of mammoths is then linked to human predation, and they propose that humans contributed to global warming: We hypothesize that the extinction of mammoths increased ifoxetine Betula cover, which would have warmed Siberia and Beringia by on average 0.2 degrees C, but regionally by up to 1 degree C. If humans were partially responsible for the extinction of mammoths, then human influences on global climate predate the origin of agriculture. ( Doughty et al., 2010) They go on to conclude that this anthropogenic regional warming trend represents the onset of the Anthropocene: “Together, these results suggest that the human influence on climate began even earlier than previously believed (Ruddiman, 2003), and that the onset of the Anthropocene should be extended back many thousand years.” (Doughty et al., 2010).