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Science 11 April 2008:
Vol. 320. no. 5873, p. 195
DOI: 10.1126/science.1153883
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Brevia

Amplification of Cretaceous Warmth by Biological Cloud Feedbacks

Lee R. Kump1* and David Pollard2

The extreme warmth of particular intervals of geologic history cannot be simulated with climate models, which are constrained by the geologic proxy record to relatively modest increases in atmospheric carbon dioxide levels. Recent recognition that biological productivity controls the abundance of cloud condensation nuclei (CCN) in the unpolluted atmosphere provides a solution to this problem. Our climate simulations show that reduced biological productivity (low CCN abundance) provides a substantial amplification of CO2-induced warming by reducing cloud lifetimes and reflectivity. If the stress of elevated temperatures did indeed suppress marine and terrestrial ecosystems during these times, this long-standing climate enigma may be solved.

1 Department of Geosciences and Earth System Science Center, Pennsylvania State University, University Park, PA 16802, USA.
2 Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA.

* To whom correspondence should be addressed. E-mail: lkump{at}psu.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)