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# Implications for climate sensitivity from the response to individual forcings

## Abstract

Climate sensitivity to doubled CO2 is a widely used metric for the large-scale response to external forcing. Climate models predict a wide range for two commonly used definitions: the transient climate response (TCR: the warming after 70 years of CO2 concentrations that rise at 1% per year), and the equilibrium climate sensitivity (ECS: the equilibrium temperature change following a doubling of CO2 concentrations). Many observational data sets have been used to constrain these values, including temperature trends over the recent past1,2,3,4,5,6, inferences from palaeoclimate7,8 and process-based constraints from the modern satellite era9,10. However, as the IPCC recently reported11, different classes of observational constraints produce somewhat incongruent ranges. Here we show that climate sensitivity estimates derived from recent observations must account for the efficacy of each forcing active during the historical period. When we use single-forcing experiments to estimate these efficacies and calculate climate sensitivity from the observed twentieth-century warming, our estimates of both TCR and ECS are revised upwards compared to previous studies, improving the consistency with independent constraints.

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## Change history

• ### 10 March 2016

In the version of this Letter originally published online, there was an error in the definition of $F 2 × CO 2$ in equation (2). The historical instantaneous radiative forcing time series was also updated to reflect land use change, which was inadvertently excluded from the forcing originally calculated from ref. 22. This has resulted in minor changes to data in Figs 1 and 2, as well as in the corresponding main text and Supplementary Information. In addition, the end of the paragraph beginning' Scaling ΔF for each of the single-forcing runs...' should have read '...the CO2-only runs' (not 'GHG-only runs'). The conclusions of the Letter are not affected by these changes. All errors have been corrected in all versions of the Letter. The authors thank Nic Lewis for his careful reading of the original manuscript that resulted in the identification of these errors.

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## Acknowledgements

Climate modelling at GISS is supported by the NASA Modeling, Analysis and Prediction Program and resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Center for Climate Simulation (NCCS) at Goddard Space Flight Center. The authors thank D. McNeall and E. Hawkins for advice on figures, and E. Hawkins, J. Gregory, M. Webb, K. Taylor and R. Pincus for helpful discussions.

## Author information

Authors

### Contributions

K.M. and G.A.S. designed the research and wrote the paper, with input from R.L.M. R.L.M. and L.S.N. provided the forcing data. L.S.N. ran the climate model experiments. All authors contributed to the interpretation of the results.

### Corresponding authors

Correspondence to Kate Marvel, Gavin A. Schmidt or Ron L. Miller.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

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Marvel, K., Schmidt, G., Miller, R. et al. Implications for climate sensitivity from the response to individual forcings. Nature Clim Change 6, 386–389 (2016). https://doi.org/10.1038/nclimate2888

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