Cited by 263Climate variability and modelsGeology and Paleoclimatology ResearchClimate Change and Environmental Impact

Increased ENSO sea surface temperature variability under four IPCC emission scenarios

Open access
Cai, Wenju, Ng, Benjamin, Wang, Guojian, Santoso, Agus, Wu, Lixin, Yang, Kai·2022·Nature Climate Change

Abstract

Sea surface temperature (SST) variability of El Niño–Southern Oscillation (ENSO) underpins its global impact, and its future change is a long-standing science issue. In its sixth assessment, the IPCC reports no systematic change in ENSO SST variability under any emission scenarios considered. However, comparison between the 20th and 21st century shows a robust increase in century-long ENSO SST variability under four IPCC plausible emission scenarios.

AI snapshot

Written from the paper’s full text.

TL;DR

Using CMIP6 models, the paper finds a robust inter-model consensus that ENSO SST variability increases in the 21st century relative to the 20th century under all four IPCC SSP scenarios, contrary to the IPCC AR6 assessment of no systematic change. The increase is statistically significant in multi-model means and is linked to stronger nonlinear Bjerknes feedback and air–sea coupling.

Key findings

  • Under SSP585, 38 out of 43 (88.4%) CMIP6 models show greater Niño3.4 SST variability in 2000–2099 than in 1900–1999; the multi-model ensemble mean increase is 16.1%, statistically significant by a bootstrap test, and 15.7% when inter-model differences in ENSO amplitude are removed.
  • Under SSP126, 34 out of 39 (87.2%) models show an increase in Niño3.4 SST variability, with a statistically significant multi-model mean increase of 11.7%.
  • Across the four SSP scenarios, inter-model consensus ranges are 78.6–88.4% for Niño3.4, 76.2–81.6% for Niño3, and 73.8–81.4% for Niño4.
  • With 50-year periods, 34 out of 43 (79.1%) models under SSP585 and 27 out of 39 (69.2%) under SSP126 produce increased ENSO SST variability; the relationship between stronger nonlinear Bjerknes feedback and greater future ENSO variability is statistically significant above the 99% confidence level.

Methods

  • Analyzed all available CMIP6 SST outputs under SSP126 (39 models), SSP245 (42), SSP370 (38), and SSP585 (43), each covering 1900–2099, using one experiment per model; historical forcing was applied to 2014 and scenario forcing thereafter.
  • Constructed monthly climatology over 1900–1999, computed SST anomalies, quadratically detrended them over the full 200 years, and calculated standard deviations over Niño3, Niño4, and Niño3.4 regions; compared 2000–2099 versus 1900–1999 and 2050–2099 versus 1965–2014.
  • Used a bootstrap method with 10,000 resamples to test whether multi-model mean increases exceed internal variability at the 95% confidence level; an alternative normalization by each model’s full 200-year standard deviation was also applied.

Limitations

  • Stated: the results are based on IPCC 21st-century transient warming scenarios, whereas studies showing decreased ENSO variability after instantaneous CO2 doubling/quadrupling concern equilibrium states; ocean mesoscale eddy-induced vertical heat transport is not resolved in CMIP6, so its effect is unknown.
  • Stated: the conclusion is based solely on CMIP6 models, while a study using 36 CMIP5 and 20 CMIP6 models finds a large spread with no inter-model consensus, suggesting sensitivity to model generation; the result is also opposite to an observed ENSO variability decline since 1999/2000, which might be masked by decadal variability and not yet detectable.
  • Evident from the text: short 30-year sampling periods, such as those used in the AR6 assessment, are strongly influenced by decadal climate fluctuations, stochastic noise, and the butterfly effect, which can obscure greenhouse-forced changes; the paper addresses this by using 100-year and 50-year periods.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1038/s41558-022-01282-z

Cites

28 of 28 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

17 of 37 cited sources checked · 12 supported · 0 flagged · accuracy not yet measured

  • Premisecitation
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    Studies based on CMIP5 models alone, or on a combination of CMIP5 and a smaller set of earlier available CMIP6 models, have found that models better simulating ENSO dynamics tend to generate increased ENSO SST variability.

    “Studies based on CMIP5 models alone, or on a combination of CMIP5 and a smaller set of earlier available CMIP6 models 9,10 , have found that models better simulating ENSO dynamics tend to generate increased ENSO SST variability.”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [9] Cai, W. et al. ENSO and greenhouse warming. Nat. Clim. Change 5, 849–859 (2015). source
    • cites [10] Cai, W. et al. Increased variability of eastern Pacific El Niño under greenhouse warming. Nature 564, 201–206 (2018). source
  • Premisecitation
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    Under greenhouse warming, an increased air-sea coupling arising from an enhanced upper equatorial ocean stratification underpins the increase in ENSO variability.

    “Under greenhouse warming, an increased air-sea coupling arising from an enhanced upper equatorial ocean stratification underpins the increase in ENSO variability 10 .”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [10] Cai, W. et al. Increased variability of eastern Pacific El Niño under greenhouse warming. Nature 564, 201–206 (2018). source

      The paper’s summary states that enhanced upper-equatorial-Pacific stratification under greenhouse warming strengthens wind–ocean coupling and increases eastern Pacific El Niño SST variance. The citing sentence broadens this specific finding to ENSO variability generally; the passage does not establish that all ENSO variability increases. (LLM, conf=0.85)

      Experimental — accuracy not yet measured
  • Premisecitation
    § Abstract

    The IPCC AR6 statement on ENSO SST variability is contrary to studies 5-7 based on CMIP6 climate models.

    “The IPCC AR6 statement on ENSO SST variability is contrary to studies 5-7 based on climate models participating in the sixth phase of the Coupled Model Intercomparison Project 8 (CMIP6).”
    Quote in the paperSubstantial claim3 of 4 sources checked
    • cites [5] Fredriksen, H.-B., Berner, J., Subramanian, A. C. & Capotondi, A. How does El Niño-Southern Oscillation change under global warming – a first look at CMIP6. Geophys. Res. Lett. 47, e2020GL090640 (2020). source

      The Results (§3.2) and Summary and Conclusion (§4) report increased ENSO-related SST variance in most of the 11 CMIP6 models, supporting the description of this paper as a CMIP6 study of ENSO SST variability. The paper does not discuss the IPCC AR6 statement or establish that its findings are contrary to it; that comparison is the citing authors’ framing. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites [6] Yang, Y. et al. Greenhouse warming intensifies north tropical Atlantic climate variability. Sci. Adv. 7, eabg9690 (2021). source
    • cites [7] Cai, W. et al. Changing El Niño–Southern Oscillation in a warming climate. Nat. Rev. Earth Environ. https://doi.org/10.1038/s43017-021-00199-z (2021). source
    • cites [8] Eyring, V. et al. Overview of the Coupled Model Intercomparison Project Phase 6 (CMIP6) experimental design and organization. Geosci. Model Dev. 9, 1937–1958 (2016). source
  • Premisecitation
    § Abstract

    There was a lack of inter-model consensus among CMIP5 models unless model selection was applied on the basis of the realism of the simulated ENSO.

    “There was a lack of inter-model consensus among available models that participated in the previous instalments of CMIP5, unless model selection was applied on the basis of the realism of the simulated ENSO 9,10 .”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [9] Cai, W. et al. ENSO and greenhouse warming. Nat. Clim. Change 5, 849–859 (2015). source
    • cites [10] Cai, W. et al. Increased variability of eastern Pacific El Niño under greenhouse warming. Nature 564, 201–206 (2018). source

      The main text says earlier assessments lacked inter-model consensus on the response of Niño3 SST variability, and the model-selection analysis says selecting models that better simulate ENSO enhanced consensus. But the same analysis reports reasonable consensus for increased E-index variance even without selection: 24 of 34 CMIP5 models (71%). The claim therefore overstates selection as necessary for consensus in general. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
  • Premisecitation
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    An inter-model consensus of increased ENSO SST variability emerges in a subset of models that simulate a reasonably realistic nonlinear positive feedback.

    “As a result, an inter-model consensus of increased ENSO SST variability emerges in a subset of models that simulate a reasonably realistic nonlinear positive feedback 10 .”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [10] Cai, W. et al. Increased variability of eastern Pacific El Niño under greenhouse warming. Nature 564, 201–206 (2018). source
  • Classified as probably not a substantial claim. 8
  • May combine two claims. 8
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    More CMIP6 models simulate realistic ENSO nonlinear feedbacks.

    “Besides some improvements in the representation of the tropical Pacific climate 20 , more CMIP6 models simulate realistic ENSO nonlinear feedbacks 7 .”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [20] Planton, Y. et al. Evaluating climate models with the CLIVAR 2020 ENSO metrics package. Bull. Am. Meteorol. Soc. 102, E193–E217 (2021). source

      The Summary reports improved ENSO patterns and other metrics in CMIP6, but it does not establish that more models simulate realistic nonlinear feedbacks. The Evaluation of ENSO processes says none of its five feedback-process metrics improved significantly from CMIP5 to CMIP6, and one degraded; it also notes that numerous nonlinear processes were not included in that short metric list. (LLM, conf=0.83)

      Experimental — accuracy not yet measured
    • cites [7] Cai, W. et al. Changing El Niño–Southern Oscillation in a warming climate. Nat. Rev. Earth Environ. https://doi.org/10.1038/s43017-021-00199-z (2021). source
  • May combine two claims.

    Premisecitation
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    Nonlinear Bjerknes feedback is particularly important: once warm SST anomalies establish deep atmospheric convection in the equatorial eastern Pacific, the response of equatorial zonal wind anomalies increases nonlinearly to further sea surface warming, amplifying El Niño growth.

    “Nonlinear Bjerknes feedback is particularly important, in which once warm SST anomalies establish deep atmospheric convection in the equatorial eastern Pacific, the response of equatorial zonal wind anomalies increases nonlinearly to further sea surface warming 19 , amplifying El Niño growth 10 .”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [19] Dommenget, D., Bayr, T. & Frauen, C. Analysis of the non-linearity in the pattern and time evolution of El Niño–Southern Oscillation. Clim. Dyn. 40, 2825–2847 (2013). source
    • cites [10] Cai, W. et al. Increased variability of eastern Pacific El Niño under greenhouse warming. Nature 564, 201–206 (2018). source
  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    A recent study based on 36 CMIP5 models and 20 CMIP6 models finds a large spread in the projected ENSO change with no inter-model consensus.

    “In addition, our conclusion is based solely on CMIP6 models, but a recent study based on 36 CMIP5 models and 20 CMIP6 models 23 finds a large spread in the projected ENSO change with no inter-model consensus; the discrepancy suggests a sensitivity of our result to model generations.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [23] Beobide-Arsuaga, G. et al. Uncertainty of ENSO-amplitude projections in CMIP5 and CMIP6 models. Clim. Dyn. 56, 3875–3888 (2021). source
  • Classified as probably not a substantial claim.

    Premisecitation
    § Bootstrap test.

    SST skewness in the eastern equatorial Pacific is an integral component of a parameter that also encapsulates skewness in the central Pacific to depict ENSO nonlinearity as a whole.

    “SST skewness in the eastern equatorial Pacific is an integral component of a parameter that also encapsulates skewness in the central Pacific to depict ENSO nonlinearity as a whole 7,10 .”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [7] Cai, W. et al. Changing El Niño–Southern Oscillation in a warming climate. Nat. Rev. Earth Environ. https://doi.org/10.1038/s43017-021-00199-z (2021). source
    • cites [10] Cai, W. et al. Increased variability of eastern Pacific El Niño under greenhouse warming. Nature 564, 201–206 (2018). source
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Abstract

    Previous studies found a stronger rainfall response to ENSO SST variability even if ENSO SST variability itself does not change.

    “consistent with findings by previous studies of a stronger rainfall response to ENSO SST variability even if ENSO SST variability itself does not change 2-4 .”
    Quote in the paperNot a substantial claim1 of 3 sources checked
    • cites [2] Power, S. B., Delage, F., Chung, C., Kociuba, G. & Keay, K. Robust twenty-first century projections of El Niño and related precipitation variability. Nature 502, 541–545 (2013). source
    • cites [3] Cai, W. et al. Increasing frequency of extreme El Niño events due to greenhouse warming. Nat. Clim. Change 4, 111–116 (2014). source
    • cites [4] 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). source
  • May combine two claims.

    Findingown data
    § Abstract

    The multi-model ensemble mean increase in Niño3.4 SST variability under SSP585 is 16.1% and statistically significant according to a Bootstrap method.

    “The multi-model ensemble mean increase (16.1%) is statistically significant according to a Bootstrap method 18 (see 'Bootstrap test' in Methods and Extended Data Fig. 1).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [18] Austin, P. C. & Tu, J. V. Bootstrap methods for developing predictive models. Am. Stat. 58, 131–137 (2004). source
  • May combine two claims.

    Findingown data
    § Abstract

    The multi-model ensemble mean increase in Niño3.4 SST variability under SSP126 is 11.7% and statistically significant.

    “The multi-model ensemble mean increase (11.7%) is statistically significant.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    Using 50-year periods (current climate 1965-2015 and future climate 2050-2099), an inter-model consensus emerges: 34 out of 43 (79.1%) models under SSP585 and 27 out of 39 (69.2%) models under SSP126 generate an increase in Niño3.4 SST variability.

    “Using statistics over another longer period, for example, 50 years of the current climate of 1965-2015 and the future climate of 2050-2099, an inter-model consensus emerges, with a total of 34 out of 43 (79.1%)models under SSP585, and 27 out of 39 (69.2%) models under SSP126, generating an increase in Niño3.4SST variability (Fig. 2a,b).”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingreasoning
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    The skewness in three model outliers that project a decrease in ENSO variability in Figs. 1 and 2 is either small (UKESM1-0-LL) or negative (BCC-CSM2-MR, CESM2).

    “As such, the skewness in three model outliers that project a decrease in ENSO variability in Figs. 1 and 2 is either small (UKESM1-0-LL) or negative (BCC-CSM2-MR, CESM2).”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data
    § Abstract

    Inter-model consensus for increased ENSO SST variability is seen in all four SSP emission scenarios, ranging between 78.6-88.4% for Niño3.4, 76.2-81.6% for Niño3, and 73.8-81.4% for Niño4 across emission scenarios.

    “Inter-model consensus is seen in all four SSP emission scenarios (Extended Data Figs.3, 4 and 5), ranging between 78.6-88.4% for Niño3.4,76.2-81.6% for Niño3, and 73.8-81.4% for Niño4 across emission scenarios.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Abstract

    Even on centennial timescales, ENSO variability is influenced by internal climate fluctuations.

    “Even on centennial timescales, ENSO variability is influenced by internal climate fluctuations 17 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [17] Li, J. et al. Interdecadal modulation of El Niño amplitude during the past millennium. Nat. Clim. Change 1, 114–118 (2011). source
  • May combine two claims.

    Interpretationown data
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    As the period for calculating ENSO statistics lengthens, the influence of internal variability tapers off, whereas the effect of greenhouse warming is better diagnosed.

    “Thus, as the period for calculating ENSO statistics lengthens, the influence of internal variability tapers off, whereas the effect of greenhouse warming is better diagnosed.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    Any greenhouse warming-induced ENSO variability change in the two decades since 1999/2000 might be masked by decadal variability and not yet detectable.

    “We also note that our result is opposite to an observed decline in ENSO variability since 1999/2000 (ref.24 ); however, any greenhouse warming-induced ENSO variability change in the two decades since 1999/2000 might be masked by decadal variability and not yet detectable.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    Ocean mesoscale eddy-induced vertical heat transport is part of ENSO dynamics.

    “Further, ocean mesoscale eddy-induced vertical heat transport is part of ENSO dynamics 22 , but is not resolved in CMIP6 models; as such, whether or how incorporation of ocean mesoscale eddies alters our conclusion is not known.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [22] Wengel, C. et al. Future high-resolution El Niño/Southern Oscillation dynamics. Nat. Clim. Change 11, 758–765 (2021). source
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Increased ENSO sea surface temperature variability under four IPCC emission scenarios

    Findings of decreased ENSO variability in equilibrium state after an instantaneous doubling/quadrupling of CO2 seemingly contradict the paper's conclusion.

    “we note findings of decreased ENSO variability 21,22 in equilibrium state after an instantaneous doubling/quadrupling of CO 2 , which seemingly contradict our conclusion”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [21] Callahan, C. W. et al. Robust decrease in El Niño/Southern Oscillation amplitude under long-term warming. Nat. Clim. Change 11, 752–757 (2021). source
    • cites [22] Wengel, C. et al. Future high-resolution El Niño/Southern Oscillation dynamics. Nat. Clim. Change 11, 758–765 (2021). source
15 of 15
  • The paper relies on this without support.

    A long analysis period reduces the effect of internal variability, allowing a better detection of the greenhouse-forced effect.

    “A long analysis period reduces the effect of internal variability, allowing a better detection of the greenhouse-forced effect.”
1 of 1

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Current-climate comparison period has two end dates

    Minor

    The text gives the current-climate period for the 50-year comparison as 1965-2015, while Methods gives it as 1965-2014. Only the latter spans 50 years when both endpoints are included.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 1

  1. IPCC Climate Change 2021: The Physical Science Basis (eds Masson-Delmotte, V. et al.) (Cambridge Univ. Press, in the press).

Cited by

Sorted by citations

Authors
Cai, W., Ng, B., Wang, G., Santoso, A., Wu, L., & Yang, K.
Venue
Nature Climate Change
Published
2022-01-31
Volume
12
Issue
3
Pages
228-231
ISSN
  • 1758-678X (ISSN-L)
  • 1758-6798
OpenAlex
W4210819470
Cited by
263
References
24
Citations by year
2026: 40 · 2025: 61 · 2024: 77 · 2023: 60 · 2022: 25
FWCI
21.85
Type
journal article
Language
en
Open access
Locations
  • Nature Climate Change (publishedVersion, cc-by)
  • RePEc: Research Papers in Economics (submittedVersion)
Funders
  • Australian Government
  • Commonwealth Scientific and Industrial Research Organisation
  • Chinese Academy of Sciences (XDB40030000, 2019YFC1509100)
  • Centre for Southern Hemisphere Oceans Research
  • Joint Research Centre
  • National Key Research and Development Program of China (2019YFC1509100)
Topics
  • Physical Sciences › Environmental Science › Global and Planetary Change › Climate variability and models
  • Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Geology and Paleoclimatology Research
  • Physical Sciences › Environmental Science › Global and Planetary Change › Climate Change and Environmental Impact
Keywords
ENSO, sea surface temperature variability, IPCC climate scenarios, climate change projections

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