El Niño/Southern Oscillation (ENSO) is the primary mode of interannual climate variability, and understanding its response to climate change is critical, but research remains divided on the direction and magnitude of that response. Some twenty-first-century simulations suggest that increased CO2 strengthens ENSO, but studies suggest that on palaeoclimate timescales higher temperatures are associated with a reduced ENSO amplitude and a weaker Pacific zonal temperature gradient, sometimes termed a ‘permanent El Niño’. Internal variability complicates this debate by masking the response of ENSO to forcing in centennial-length projections. Here we exploit millennial-length climate model simulations to disentangle forced changes to ENSO under transient and equilibrated conditions. On transient timescales, models show a wide spread in ENSO responses but, on millennial timescales, nearly all of them show decreased ENSO amplitude and a weakened Pacific zonal temperature gradient. Our results reconcile differences among twenty-first-century simulations and suggest that CO2 forcing dampens ENSO over the long term.
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All processed data required to reproduce the results of this study are available at https://github.com/ccallahan45/Callahan-et-al_NCC_2021/, archived on Zenodo at https://doi.org/10.5281/zenodo.4718010 (ref. 74). Raw LongRunMIP data are not provided due to large file sizes, but these data are publicly available at https://data.iac.ethz.ch/longrunmip/, with further information available at http://www.longrunmip.org.
Analysis code required to reproduce the results of this study is available at https://github.com/ccallahan45/Callahan-et-al_NCC_2021/, archived on Zenodo at https://doi.org/10.5281/zenodo.4718010 (ref. 74).
Cayan, D. R., Redmond, K. T. & Riddle, L. G. ENSO and hydrologic extremes in the Western United States. J. Clim. 12, 2881–2893 (1999).
Lehodey, P., Bertignac, M., Hampton, J., Lewis, A. & Picaut, J. El Niño Southern Oscillation and tuna in the western Pacific. Nature 389, 715–718 (1997).
Harger, J. R. E. ENSO variations and drought occurrence in Indonesia and the Philippines. Atmos. Environ. 29, 1943–1955 (1995).
McPhaden, M. J., Zebiak, S. E. & Glantz, M. H. ENSO as an integrating concept in Earth science. Science 314, 1740–1745 (2006).
Philip, S. & Oldenborgh, G. J. V. Shifts in ENSO coupling processes under global warming. Geophys. Res. Lett. 33, L11704 (2006).
Cai, W. et al. ENSO and greenhouse warming. Nat. Clim. Change 5, 849–859 (2015).
Collins, M. et al. The impact of global warming on the tropical Pacific Ocean and El Nino. Nat. Geosci. 3, 391–397 (2010).
Cai, W. et al. Increasing frequency of extreme El Niño events due to greenhouse warming. Nat. Clim. Change 4, 111–116 (2014).
Cai, W. et al. Increased frequency of extreme La Niña events under greenhouse warming. Nat. Clim. Change 5, 132–137 (2015).
Cai, W. et al. Increased variability of eastern Pacific El Niño under greenhouse warming. Nature 564, 201–206 (2018).
Rashid, H. A., Hirst, A. C. & Marsland, S. J. An atmospheric mechanism for ENSO amplitude changes under an abrupt quadrupling of CO2 concentration in CMIP5 models. Geophys. Res. Lett. 43, 1687–1694 (2016).
Kohyama, T. & Hartmann, D. L. Nonlinear ENSO warming suppression. J. Clim. 30, 4227–4251 (2017).
Wittenberg, A. T. Are historical records sufficient to constrain ENSO simulations? Geophys. Res. Lett. 36, L12702 (2009).
Chen, C., Cane, M. A., Wittenberg, A. T. & Chen, D. ENSO in the CMIP5 simulations: life cycle, diversity, and responses to climate change. J. Clim. 30, 775–801 (2017).
Maher, N., Matei, D., Milinski, S. & Marotzke, J. ENSO change in climate projections: forced response or internal variability? Geophys. Res. Lett. 45, 11390–11398 (2018).
Sun, C. et al. Uncertainties in simulated El Niño–Southern Oscillation arising from internal climate variability. Atmos. Sci. Lett. 19, e805 (2018).
Zheng, X.-T., Hui, C. & Yeh, S.-W. Response of ENSO amplitude to global warming in CESM large ensemble: uncertainty due to internal variability. Clim. Dyn. 50, 4019–4035 (2018).
Meehl, G. A. & Washington, W. M. El Niño-like climate change in a model with increased atmospheric CO2 concentrations. Nature 382, 56–60 (1996).
Vecchi, G. A. & Soden, B. J. Global warming and the weakening of the tropical circulation. J. Clim. 20, 4316–4340 (2007).
An, S.-I., Kug, J.-S., Ham, Y.-G. & Kang, I.-S. Successive modulation of ENSO to the future greenhouse warming. J. Clim. 21, 3–21 (2008).
Wara, M. W., Ravelo, A. C. & Delaney, M. L. Permanent El Niño-like conditions during the Pliocene warm period. Science 309, 758–761 (2005).
Fedorov, A. V. et al. The Pliocene paradox (mechanisms for a permanent El Niño). Science 312, 1485–1489 (2006).
Zhang, Y. G., Pagani, M. & Liu, Z. A 12-million-year temperature history of the tropical Pacific Ocean. Science 344, 84–87 (2014).
Yang, H. & Zhang, Q. Anatomizing the ocean’s role in ENSO changes under global warming. J. Clim. 21, 6539–6555 (2008).
Ivany, L. C., Brey, T., Huber, M., Buick, D. P. & Schone, B. R. El Niño in the Eocene greenhouse recorded by fossil bivalves and wood from Antarctica. Geophys. Res. Lett. 38, L16709 (2011).
Seager, R. et al. Strengthening tropical Pacific zonal sea surface temperature gradient consistent with rising greenhouse gases. Nat. Clim. Change 9, 517–522 (2019).
Chung, E.-S. et al. Reconciling opposing Walker circulation trends in observations and model projections. Nat. Clim. Change 9, 405–412 (2019).
Rugenstein, M. et al. LongRunMIP: motivation and design for a large collection of millennial-length AOGCM simulations. Bull. Am. Meteorol. Soc. 100, 2551–2570 (2019).
McPhaden, M. J., Lee, T. & McClurg, D. El Niño and its relationship to changing background conditions in the tropical Pacific Ocean. Geophys. Res. Lett. 38, L15709 (2011).
Stevenson, S., Wittenberg, A. T., Fasullo, J., Coats, S. & Otto-Bliesner, B. Understanding diverse model projections of future extreme El Niño. J. Clim. 34, 449–464 (2020).
Wang, B. et al. Historical change of El Niño properties sheds light on future changes of extreme El Niño. Proc. Natl Acad. Sci. USA 116, 22512–22517 (2019).
Ng, B., Cai, W., Cowan, T. & Bi, D. Impacts of low-frequency internal climate variability and greenhouse warming on the El Niño-Southern Oscillation. J. Clim. 34, 2205–2218 (2020).
Wyman, D. A., Conroy, J. L. & Karamperidou, C. The tropical pacific ENSO–mean state relationship in climate models over the last millennium. J. Clim. 33, 7539–7551 (2020).
Kohyama, T., Hartmann, D. L. & Battisti, D. S. La Niña-like mean-state response to global warming and potential oceanic roles. J. Clim. 30, 4207–4225 (2017).
Knutson, T. R. & Manabe, S. Time-mean response over the tropical Pacific to increased CO2 in a coupled ocean–atmosphere model. J. Clim. 8, 2181–2199 (1995).
Zhang, L. & Karnauskas, K. B. The role of tropical interbasin SST gradients in forcing Walker circulation trends. J. Clim. 30, 499–508 (2017).
Coats, S. & Karnauskas, K. A role for the equatorial undercurrent in the ocean dynamical thermostat. J. Clim. 31, 6245–6261 (2018).
Olonscheck, D., Rugenstein, M. & Marotzke, J. Broad consistency between observed and simulated trends in sea surface temperature patterns. Geophys. Res. Lett. 47, e2019GL086773 (2020).
Chemke, R. & Polvani, L. M. Opposite tropical circulation trends in climate models and in reanalyses. Nat. Geosci. 12, 528–532 (2019).
Lloyd, J., Guilyardi, E., Weller, H. & Slingo, J. The role of atmosphere feedbacks during ENSO in the CMIP3 models. Atmos. Sci. Lett. 10, 170–176 (2009).
Lloyd, J., Guilyardi, E. & Weller, H. The role of atmosphere feedbacks during ENSO in the CMIP3 models. Part III: the shortwave flux feedback. J. Clim. 25, 4275–4293 (2012).
Wang, G. et al. Continued increase of extreme El Niño frequency long after 1.5 C warming stabilization. Nat. Clim. Change 7, 568–572 (2017).
Guilyardi, E. et al. Atmosphere feedbacks during ENSO in a coupled GCM with a modified atmospheric convection scheme. J. Clim. 22, 5698–5718 (2009).
Middlemas, E. A., Clement, A. C., Medeiros, B. & Kirtman, B. Cloud radiative feedbacks and El Niño–Southern Oscillation. J. Clim. 32, 4661–4680 (2019).
Bloch-Johnson, J., Rugenstein, M. & Abbot, D. S. Spatial radiative feedbacks from internal variability using multiple regression. J. Clim. 33, 4121–4140 (2020).
Cai, W. et al. Butterfly effect and a self-modulating El Niño response to global warming. Nature 585, 68–73 (2020).
Tierney, J. E., Haywood, A. M., Feng, R., Battacharya, T. & Otto-Bleisner, B. L. Pliocene warmth consistent with greenhouse gas forcing. Geophys. Res. Lett. 46, 9136–9144 (2019).
Stevenson, S., Fox-Kemper, B., Jochum, M., Rajagopalan, B. & Yeager, S. G. ENSO model validation using wavelet probability analysis. J. Clim. 23, 5540–5547 (2010).
Yeager, S. G., Shields, C. A., Large, W. G. & Hack, J. J. The low-resolution CCSM3. J. Clim. 19, 2545–2566 (2006).
Danabasoglu, G. & Gent, P. R. Equilibrium climate sensitivity: is it accurate to use a slab ocean model? J. Clim. 22, 2494–2499 (2009).
Gent, P. R. et al. The Community Climate System Model version 4. J. Clim. 24, 4973–4991 (2011).
Danabasoglu, G. et al. The CCSM4 ocean component. J. Clim. 25, 1361–1389 (2012).
Rugenstein, M. A. A., Sedlacek, J. & Knutti, R. Nonlinearities in patterns of long-term ocean warming. Geophys. Res. Lett. 43, 3380–3388 (2016).
Voldoire, A. et al. Evaluation of CMIP6 DECK experiments with CNRM-CM6-1. J. Adv. Model. Earth Syst. 11, 2177–2213 (2019).
Donner, L. J., Wyman, B. L. & Hemler, R. S. et al. The dynamical core, physical parameterizations, and basic simulation characteristics of the atmospheric component AM3 of the GFDL Global Coupled Model CM3. J. Clim. 24, 3484–3519 (2011).
Paynter, D., Frolicher, T. L., Horowitz, L. W. & Silvers, L. G. Equilibrium climate sensitivity obtained from multimillennial runs of two GFDL climate models. J. Geophys. Res. Atmos. 123, 1921–1941 (2018).
Dunne, J. P. et al. GFDL’s ESM2 global coupled climate-carbon earth system models. Part I: physical formulation and baseline simulation characteristics. J. Clim. 25, 6646–6665 (2012).
Miller, R. L. et al. CMIP5 historical simulations (1850–2012) with GISS ModelE2. J. Adv. Model. Earth Syst. 6, 441–478 (2014).
Nazarenko, L. et al. Future climate change under RCP emission scenarios with GISS ModelE2. J. Adv. Model. Earth Syst. 7, 244–267 (2015).
Rind, D. et al. Multicentury instability of the Atlantic meridional circulation in rapid warming simulations with GISS ModelE2. J. Geophys. Res. Atmos. 123, 6331–6355 (2018).
Schmidt, G. A. et al. Configuration and assessment of the GISS ModelE2 contributions to the CMIP5 archive. J. Adv. Model. Earth Syst. 6, 141–184 (2014).
Cox, P. M., Betts, R. A., Jones, C. D., Spall, S. A. & Totterdell, I. J. Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature 408, 184–187 (2000).
Cao, L., Duan, L., Bala, G. & Caldeira, K. Simulated long-term climate response to idealized solar geoengineering. Geophys. Res. Lett. 43, 2209–2217 (2016).
Dufresne, J.-L., Foujols, M.-A. & Denvil, S. et al. Climate change projections using the IPSL-CM5 Earth System Model: from CMIP3 to CMIP5. Clim. Dyn. 40, 2123–2165 (2013).
Hasumi, H. & Emori, S. K-1 coupled GCM (MIROC) description. https://ccsr.aori.u-tokyo.ac.jp/~hasumi/miroc_description.pdf (2004).
Yamamoto, A. et al. Global deep-ocean oxygenation by enhanced ventilation in the Southern Ocean under long-term global warming. Glob. Biogeochem. Cycles 29, 1801–1815 (2015).
Yoshimori, M. et al. A review of progress towards understanding the transient global mean surface temperature response to radiative perturbation. Prog. Earth Planet. Sci. 3, 21 (2016).
Mauritsen, T. et al. Developments in the MPI-M Earth System Model version 1.2 MPI-ESM1.2 and its response to increasing CO2. J. Adv. Model. Earth Syst. 11, 998–1038 (2019).
Rohrschneider, T., Stevens, B. & Mauritsen, T. On simple representations of the climate response to external radiative forcing. Clim. Dyn. 53, 3131–3145 (2019).
Vecchi, G. A. et al. Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing. Nature 441, 73–76 (2006).
Rugenstein, M. et al. Equilibrium climate sensitivity estimated by equilibrating climate models. Geophys. Res. Lett. 47, e2019GL083898 (2020).
Huang, P. W. et al. NOAA Extended Reconstruction Sea Surface Temperature (ERSST), Version 5. NOAA National Centers for Environmental Information https://doi.org/10.7289/V5T72FNM (2017).
Rayner, N. A. et al. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res. 108, 4407 (2003).
Callahan, C. W. Robust decrease in ENSO amplitude under long-term warming. Zenodo https://zenodo.org/record/4718010 (2021).
We thank M. Jansen, N. Maher, J. Franke and K. Schwarzwald for helpful discussions and insights. This research was performed as part of the Center for Robust Decision-making on Climate and Energy Policy at the University of Chicago, funded by NSF through the Decision Making Under Uncertainty programme (grant no. SES-1463644 to E.J.M.). Computing resources were provided by the University of Chicago Research Computing Center and Dartmouth College Research Computing. M.R. is funded by the Alexander von Humboldt foundation. This project received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 786427, project Couplet) to J.B.-J. Finally, this work would not have been possible without the efforts of the contributors to the LongRunMIP project.
The authors declare no competing interests.
Peer review information Nature Climate Change thanks the anonymous reviewers for their contribution to the peer review of this work.
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Callahan, C.W., Chen, C., Rugenstein, M. et al. Robust decrease in El Niño/Southern Oscillation amplitude under long-term warming. Nat. Clim. Chang. 11, 752–757 (2021). https://doi.org/10.1038/s41558-021-01099-2
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