# Emergent constraints on Earth’s transient and equilibrium response to doubled CO2 from post-1970s global warming

## Abstract

Future global warming is determined by both greenhouse gas emission pathways and Earth’s transient and equilibrium climate response to doubled atmospheric CO2. Energy-balance inference from the instrumental record typically yields central estimates for the transient response of around 1.3 K and the equilibrium response of 1.5–2.0 K, which is at the lower end of those from contemporary climate models. Uncertainty arises primarily from poorly known aerosol-induced cooling since the early industrialization era and a temporary cooling induced by evolving sea surface temperature patterns. Here we present an emergent constraint on post-1970s warming, taking advantage of the weakly varying aerosol cooling during this period. We derive a relationship between the transient response and the post-1970s warming in Coupled Model Intercomparison Project Phase 5 (CMIP5) models. We thereby constrain, with the observations, the transient response to 1.67 K (1.17–2.16 K, 5–95th percentiles). This is a 20% increase relative to energy-balance inference stemming from previously neglected upper-ocean energy storage. For the equilibrium climate sensitivity we obtain a best estimate of 2.83 K (1.72–4.12 K) contingent on the temporary pattern effects exhibited by climate models. If the real world’s surface temperature pattern effects are substantially stronger, then the upper-bound equilibrium sensitivity may be higher than found here.

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## Data availability

CMIP5 data can be accessed through ESGF nodes. HadCRUT4 data are provided by the UK Met Office Hadley Centre. The NOAA/OAR/ESRL PSD dataset website provided the NOAA GlobalTemp dataset as well as the GISTEMP dataset. BEST was downloaded from the Berkeley Earth website. The Cowtan and Way 2.0 dataset is available from the author’s website (https://www-users.york.ac.uk/~kdc3/papers/coverage2013/series.html). Forcing data comes from the IPCC AR5 WG1 report24.

## Code availability

An archive with scripts to conduct the data download, preprocess the data, analyse them and obtain the figures supporting this study is archived by the Max Planck Institute for Meteorology and can be obtained by contacting either the corresponding author or publications@mpimet.mpg.de.

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## Acknowledgements

D.J.-d.-l.-C. and T.M. were supported by the Max-Planck-Gesellschaft, and T.M. received funding from European Research Council Consolidator Grant No. 770765 and European Union Horizon 2020 project no. 820829. The study benefitted from comments and input from K. Armour, S. Bühler, A. Dessler, S. Fiedler, P. Forster, R. Pincus, B. Stevens and M. Watanabe. Computational resources were made available by Deutsches Klimarechenzentrum through support from Bundesministerium für Bildung und Forschung.

## Author information

D.J.-d.-l.-C. and T.M. developed the methodology and wrote the manuscript.

Correspondence to Diego Jiménez-de-la-Cuesta.

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### Competing interests

The authors declare no competing interests.

Peer review information Primary Handling Editor(s): Heike Langenberg.

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## Supplementary information

### Supplementary Information

Supplementary figures and tables.

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Jiménez-de-la-Cuesta, D., Mauritsen, T. Emergent constraints on Earth’s transient and equilibrium response to doubled CO2 from post-1970s global warming. Nat. Geosci. 12, 902–905 (2019) doi:10.1038/s41561-019-0463-y