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Snyder replies

Nature volume 547, pages E17–E18 (2017)Cite this article

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Replying to G. A. Schmidt et al. Nature 547, 10.1038/nature22803 (2017)

The Earth system sensitivity (ESS) summarizes the feedback behaviour of Earth’s climate system and includes ice sheets, vegetation and dust as internal feedbacks. This definition of the ESS is in contrast to that of the equilibrium climate sensitivity (ECS), for which those feedbacks are considered external forcings1,2. As previously quantified from palaeoclimate records, the ESS3,4,5,6,7 and palaeoclimate sensitivity parameter S[GHG] (ref. 2) do not test causation, but summarize the past aggregate, correlational relationships among those feedbacks. In the accompanying Comment8, Schmidt et al. contend that I miscalculated the ESS by defining it to include all changes to ice sheets as internal feedbacks9. However, previous research had applied the same definition of the ESS3,4,5,6,7 or S[GHG] (ref. 2), yielding estimates of the ESS of 8.6 ± 2.8 °C (1σ)2, 7.4 °C (6.2–9.1 °C, 95% confidence interval)3 and 6 °C (refs 4, 5) from the late Pleistocene and exceeding 6 °C from Cenozoic periods with large ice sheets6. These values are comparable to my estimate of 9 °C (7–13 °C, 95% credible interval)9. Moreover, my estimates of the ESS9 are consistent with recent IPCC estimates of the ECS1.

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  1. Interdisciplinary Program in Environment and Resources, Stanford University, Stanford, 94305, California, USA

    Carolyn W. Snyder

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Snyder, C. Snyder replies. Nature 547, E17–E18 (2017). https://doi.org/10.1038/nature22804

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