Using Fossil Leaves for the Reconstruction of Cenozoic Paleoatmospheric CO2 Concentrations
Wolfram M. Kürschner, Friederike Wagner, David L. Dilcher, Henk Visscher, 2001. "Using Fossil Leaves for the Reconstruction of Cenozoic Paleoatmospheric CO2 Concentrations", Geological Perspectives of Global Climate Change, Lee C. Gerhard, William E. Harrison, Bernold M. Hanson
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In the present contribution, we address the relationship between climate and atmospheric carbon-dioxide (CO2) concentration on different timescales, from long-term trends through the Cenozoic to short-term variations in the recent past. The inverse relationship between stomatal frequency of angiosperm leaves and the CO2 concentration of the ambient air is used as a robust method for quantifying paleoatmospheric CO2 levels. Short-term, century-scaled CO2 fluctuations are reflected in the stomatal frequency pattern of early Holocene birch leaves. Changes in paleoatmospheric CO2 correlate with major environmental and climatic changes, indicated in the terrestrial palynological record and by δ18O fluctuations in polar ice. Further evidence for significant perturbations in the global carbon cycle during the early Holocene is revealed by concomitant changes in atmospheric radiocarbon (14C) content. Warm climatic phases during the Cenozoic represent a particularly challenging test of our understanding of stomatal frequency response to past CO2 concentrations. The principal question is whether an enhanced greenhouse effect was responsible for these periods of increased global temperature. The data available so far indicate that during the late Neogene, when the temperature was significantly increased for the last time in the geological history, the paleoatmospheric CO2 concentration was close to the present level of about 360 parts per million volume (ppmv). During the peak warmth of the early middle Eocene, however, paleoatmospheric CO2 concentration was significantly elevated, to about 500 ppmv.