Effects of Syn-Pandemic Reforestation on Atmospheric Carbon Dioxide From 1500 to 1700 A.D.
Abstract
Recent analysis of paleoclimate proxies suggests that biomass burning by humans during the past eight millennia produced quantities of CO2 sufficient to counteract the effects of decreasing insolation driven by orbital variations and thus prevented ice sheet expansion. Correlation between periods of declining population and biomass burning, such as implied by the synchroneity of the American pandemics and decreasing atmospheric CO2 concentration during the 16th-18th centuries, provides an important test of the extent to which pre-industrial anthropogenic activity affected the atmospheric greenhouse gas budget. Numerous studies have attributed the ~5 ppm decline of atmospheric CO2 concentration, as well as the synchronous ~0.1 per mil increase of the δ13C of atmospheric CO2 between 1500 and 1700 A.D., to the effects of Little Ice Age cooling. However, this interpretation is not supported by recent multiproxy-based surface temperature reconstructions, which demonstrate a diminutive global temperature anomaly of ~0.1 C that was unlikely to have independently produced the distinct effect observed in atmospheric CO2 concentration. Alternatively, it is possible that a decline in CO2 concentration driven by massive reforestation produced cooling as a by-product. The timing and magnitude of changes in both the concentration and carbon-isotope composition of atmospheric CO2 recorded by globally distributed climate proxies from the tropics (sponges), temperate latitudes (tree rings), and polar regions (ice cores) are compatible with fixation of >10 Gt C due to reforestation. Reforestation, which explains pre-industrial atmospheric CO2 variations between 1500 and 1700 A.D. in a manner more consistent with the global surface temperature record than explanations requiring substantial cooling, presumably occurred on lands that were cultivated and seasonally burned, then subsequently abandoned, by indigenous Americans who perished in pandemics during European conquest. The present proxy data point to reforestation in the wake of the American pandemic, with its consequent affects on atmospheric CO2, as unique in human history. These findings redefine the duration and extent of human activities affecting composition of the atmosphere during the past millennium. The anthropogenic influence on the partial pressure of atmospheric CO2 since ~1800 A.D. is well documented by the exponential rise in concentration and simultaneous decline in δ13C of atmospheric CO2, but these recent trends represent dramatic reversals in the behavior of atmospheric CO2 concentration and δ13C prior to the Industrial Revolution between 1500 and 1700. During this time the concentration of atmospheric CO2 decreased and its δ13C increased due to land use changes resulting from pandemics that killed ~90% of the indigenous American population (~50 million people).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMPP51B0589N
- Keywords:
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- 1616 Climate variability (1635;
- 3305;
- 3309;
- 4215;
- 4513);
- 1631 Land/atmosphere interactions (1218;
- 1843;
- 3322);
- 4902 Anthropogenic effects (1803;
- 4802);
- 4930 Greenhouse gases;
- 4932 Ice cores (0724)