11. Graham D. Farquhar, "Carbon Dioxide and Vegetation," Science, 278, 1411 (21 Nov 97).This article contrasts the processing of carbon dioxide to form vegetation at the Last Glacial Maximum, 20,000 years ago, when the concentration was only 180 ppm, and the Early Interglacial, 10,000 years ago, when the concentration had risen to 270 ppm. The limited carbon dioxide available at the Last Glacial Maximum sufficed only to form grasses, via the C4 pathway. The increased carbon dioxide concentration at the Early Interglacial produced more vegetation, specifically trees, through the C3 pathway, which requires only half as much water (thus producing the effect of greater rainfall). The C3 pathway also produces a different isotopic distribution of carbon in vegetation than C4. This trend of effectively increasing the amount of water for vegetation growth with increased carbon dioxide concentration is expected to continue, but perhaps not so strongly.
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