Letter abstract
Nature Geoscience 1, 43 - 48 (2008)
Published online: 9 December 2007 | doi:10.1038/ngeo.2007.29
Subject Categories: Palaeoclimate and palaeoceanography | Atmospheric science
Atmospheric carbon dioxide linked with Mesozoic and early Cenozoic climate change
Benjamin J. Fletcher1, Stuart J. Brentnall1, Clive W. Anderson2, Robert A. Berner3 & David J. Beerling1
The relationship between atmospheric carbon dioxide (CO2) and climate in the Quaternary period has been extensively investigated, but the role of CO2 in temperature changes during the rest of Earth's history is less clear1. The range of geological evidence for cool periods during the high CO2 Mesozoic 'greenhouse world'2, 3 of high atmospheric CO2 concentrations, indicated by models4 and fossil soils5, has been particularly difficult to interpret. Here, we present high-resolution records of Mesozoic and early Cenozoic atmospheric CO2 concentrations from a combination of carbon-isotope analyses of non-vascular plant (bryophyte) fossils and theoretical modelling6, 7. These records indicate that atmospheric CO2 rose from 
420 p.p.m.v. in the Triassic period (about 200 million years ago) to a peak of 1,130 p.p.m.v. in the Middle Cretaceous (about 100 million years ago). Atmospheric CO2 levels then declined to 680 p.p.m.v. by 60 million years ago. Time-series comparisons show that these variations coincide with large Mesozoic climate shifts8, 9, 10, in contrast to earlier suggestions of climate–CO2 decoupling during this interval1. These reconstructed atmospheric CO2 concentrations drop below the simulated threshold for the initiation of glaciations11 on several occasions and therefore help explain the occurrence of cold intervals in a 'greenhouse world'3.
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
- Department of Probability and Statistics, University of Sheffield, Sheffield S10 2TN, UK
- Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA
Correspondence to: David J. Beerling1 e-mail: d.j.beerling@sheffield.ac.uk
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