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Updated: Jul 17, 2026

A CO2 Concentration Gradient Facility for Testing CO2 Enrichment and Soil Effects on Grassland Ecosystem Function
Published on: November 21, 2015
Late miocene atmospheric CO(2) concentrations and the expansion of C(4) grasses
1Department of Geosciences, The Pennsylvania State University, University Park, PA 16872, USA.
Abstract:
The global expansion of C(4) grasslands in the late Miocene has been attributed to a large-scale decrease in atmospheric carbon dioxide (CO(2)) concentrations. This triggering mechanism is controversial, in part because of a lack of direct evidence for change in the partial pressure of CO(2) (pCO(2)) and because other factors are also important determinants in controlling plant-type distributions. Alkenone-based pCO(2) estimates for the late Miocene indicate that pCO(2) increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago. The estimates presented here provide no evidence for major changes in pCO(2) during the late Miocene. Thus, C(4) plant expansion was likely driven by additional factors, possibly a tectonically related episode of enhanced low-latitude aridity or changes in seasonal precipitation patterns on a global scale (or both).
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