HR: 0800h
AN: PP51B-0589    [Abstracts]
TI: Effects of Syn-Pandemic Reforestation on Atmospheric Carbon Dioxide From 1500 to 1700 A.D.
AU: * Nevle, R J
EM: rnevle@bcp.org
AF: Bellarmine College Preparatory, 960 West Hedding, San Jose, CA 95126-1215 United States
AU: Bird, D K
PP51B-0589 AF: Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Braun Hall, Building 320, Stanford, CA 94305-2115 United States
AB: 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 16^th-18^th 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).
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 4902 Anthropogenic effects (1803, 4802)
DE: 4930 Greenhouse gases
DE: 4932 Ice cores (0724)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005