Proxy evidence for state-dependence of climate sensitivity in the Eocene greenhouse

E. Anagnostou*, E. H. John, T. L. Babila, P. F. Sexton, A. Ridgwell, D. J. Lunt, P. N. Pearson, T. B. Chalk, R. D. Pancost, G. L. Foster

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

62 Citations (Scopus)


Despite recent advances, the link between the evolution of atmospheric CO2 and climate during the Eocene greenhouse remains uncertain. In particular, modelling studies suggest that in order to achieve the global warmth that characterised the early Eocene, warmer climates must be more sensitive to CO2 forcing than colder climates. Here, we test this assertion in the geological record by combining a new high-resolution boron isotope-based CO2 record with novel estimates of Global Mean Temperature. We find that Equilibrium Climate Sensitivity (ECS) was indeed higher during the warmest intervals of the Eocene, agreeing well with recent model simulations, and declined through the Eocene as global climate cooled. These observations indicate that the canonical IPCC range of ECS (1.5 to 4.5 °C per doubling) is unlikely to be appropriate for high-CO2 warm climates of the past, and the state dependency of ECS may play an increasingly important role in determining the state of future climate as the Earth continues to warm.

Original languageEnglish
Article number4436
JournalNature Communications
Issue number1
Publication statusPublished - 1 Dec 2020


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