Post by Swamp Gas on Apr 14, 2007 12:03:46 GMT -5
stephenschneider.stanford.edu/Publications/PDF_Papers/Ruddiman2003.pdf
Abstract. The anthropogenic era is generally thought to have begun 150 to 200 years ago, when
the industrial revolution began producing CO2 and CH4 at rates sufficient to alter their compositions
in the atmosphere. A different hypothesis is posed here: anthropogenic emissions of these gases
first altered atmospheric concentrations thousands of years ago. This hypothesis is based on three
arguments. (1) Cyclic variations in CO2 and CH4 driven by Earth-orbital changes during the last
350,000 years predict decreases throughout the Holocene, but the CO2 trend began an anomalous
increase 8000 years ago, and the CH4 trend did so 5000 years ago. (2) Published explanations for
these mid- to late-Holocene gas increases based on natural forcing can be rejected based on paleoclimatic
evidence. (3) A wide array of archeological, cultural, historical and geologic evidence points
to viable explanations tied to anthropogenic changes resulting from early agriculture in Eurasia,
including the start of forest clearance by 8000 years ago and of rice irrigation by 5000 years ago. In
recent millennia, the estimated warming caused by these early gas emissions reached a global-mean
value of ?0.8 ?C and roughly 2 ?C at high latitudes, large enough to have stopped a glaciation of
northeastern Canada predicted by two kinds of climatic models. CO2 oscillations of ~10 ppm in the
last 1000 years are too large to be explained by external (solar-volcanic) forcing, but they can be
explained by outbreaks of bubonic plague that caused historically documented farm abandonment
in western Eurasia. Forest regrowth on abandoned farms sequestered enough carbon to account for
the observed CO2 decreases. Plague-driven CO2 changes were also a significant causal factor in
temperature changes during the Little Ice Age (1300–1900 AD).
Abstract. The anthropogenic era is generally thought to have begun 150 to 200 years ago, when
the industrial revolution began producing CO2 and CH4 at rates sufficient to alter their compositions
in the atmosphere. A different hypothesis is posed here: anthropogenic emissions of these gases
first altered atmospheric concentrations thousands of years ago. This hypothesis is based on three
arguments. (1) Cyclic variations in CO2 and CH4 driven by Earth-orbital changes during the last
350,000 years predict decreases throughout the Holocene, but the CO2 trend began an anomalous
increase 8000 years ago, and the CH4 trend did so 5000 years ago. (2) Published explanations for
these mid- to late-Holocene gas increases based on natural forcing can be rejected based on paleoclimatic
evidence. (3) A wide array of archeological, cultural, historical and geologic evidence points
to viable explanations tied to anthropogenic changes resulting from early agriculture in Eurasia,
including the start of forest clearance by 8000 years ago and of rice irrigation by 5000 years ago. In
recent millennia, the estimated warming caused by these early gas emissions reached a global-mean
value of ?0.8 ?C and roughly 2 ?C at high latitudes, large enough to have stopped a glaciation of
northeastern Canada predicted by two kinds of climatic models. CO2 oscillations of ~10 ppm in the
last 1000 years are too large to be explained by external (solar-volcanic) forcing, but they can be
explained by outbreaks of bubonic plague that caused historically documented farm abandonment
in western Eurasia. Forest regrowth on abandoned farms sequestered enough carbon to account for
the observed CO2 decreases. Plague-driven CO2 changes were also a significant causal factor in
temperature changes during the Little Ice Age (1300–1900 AD).