Overestimate of committed warming

Gavin A Schmidt; Jeff Severinghaus; Ayako Abe-Ouchi; Richard B Alley; Wallace Broecker; Ed Brook; David Etheridge; Kenji Kawamura; Ralph F Keeling; Margaret Leinen; Kate Marvel; Thomas F Stocker

doi:10.1038/nature22803

Overestimate of committed warming

Nature. 2017 Jul 12;547(7662):E16-E17. doi: 10.1038/nature22803.

Authors

Gavin A Schmidt¹, Jeff Severinghaus², Ayako Abe-Ouchi^{3

4}, Richard B Alley⁵, Wallace Broecker⁶, Ed Brook⁷, David Etheridge⁸, Kenji Kawamura^{9

10

11}, Ralph F Keeling², Margaret Leinen², Kate Marvel^{1

12}, Thomas F Stocker¹³

Affiliations

¹ NASA Goddard Institute for Space Studies, New York, New York 10025, USA.
² Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA.
³ Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan.
⁴ Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, Japan.
⁵ Department of Geosciences, Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
⁶ Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, New York 10964, USA.
⁷ College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA.
⁸ CSIRO Climate Science Centre, Aspendale, Victoria, Australia.
⁹ National Institute for Polar Research, Tachikawa, Tokyo 190-8518, Japan.
¹⁰ Department of Polar Science, SOKENDAI (The Graduate University for Advanced Studies), Tachikawa, Tokyo 190-8518, Japan.
¹¹ Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan.
¹² Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10025, USA.
¹³ Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.

Abstract

Palaeoclimate variations are an essential component in constraining future projections of climate change as a function of increasing anthropogenic greenhouse gases. The Earth System Sensitivity (ESS) describes the multi-millennial response of Earth (in terms of global mean temperature) to a doubling of CO₂ concentrations. A recent study used a correlation of inferred temperatures and radiative forcing from greenhouse gases over the past 800,000 years to estimate the ESS from present day CO₂ is about 9°C, and to imply a long-term commitment of 3–7°C even if greenhouse gas levels remain at present-day concentrations. However, we demonstrate that the methodology of ref. does not reliably estimate the ESS in the presence of orbital forcing of ice age cycles and therefore conclude that the inferred present-day committed warming is considerably overestimated. There is a Reply to this Comment by Snyder, C. W. Nature 547, http://dx.doi.org/10.1038/nature22804 (2017).