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Supplementary material
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The Kiel Climate Model (KCM, Park et al. 2009) consists of the ECHAM5 atmosphere
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general circulation model on a T31 horizontal grid (3.75° x 3.75°) with 19 vertical levels,
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which is coupled through the OASIS coupler to the NEMO ocean-sea ice model on a 2˚
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Mercator mesh amounting on average to 1.3°. Enhanced meridional resolution of 0.5° is
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employed in the equatorial region and the ocean model is run with 31 levels. A list of
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references can be obtained from http://www.geomar.de/en/research/fb1/fb1-me/research-
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topics/climate-modelling/kcms/. Annual-mean SST biases (Fig. S1), although significant, are
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typical for state-of-the-art climate models. The spectrum of monthly-mean SST anomalies in
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the Niño3 region (150°W-90°W, 5°S-5°N) compares well to that calculated from observations
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(Fig. S2). In comparison to the models participating in Coupled Model Intercomparison
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Project Phase 5 (CMIP5, Taylor et al. 2012), the KCM is well within the multi-model
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distributions concerning gross indices: SST in the Niño4 region (160°E-150°W, 5°S-5°N),
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equatorial Pacific zonal SST contrast (Niño4-Niño3), and standard deviation of SST
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anomalies in the Niño3 region (Figs. S3A, B). The variability is somewhat overestimated and
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it also extends too far westward (Fig. S4), biases also seen in many other models. Consistent
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with previous studies (e.g., Wittenberg et al. 2009), a strong decadal to centennial modulation
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of ENSO amplitude is simulated in the control integration of the KCM (Fig. 1), in which
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atmospheric CO2 is constant at 348 ppm.
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Supplementary figures
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Figure S1: Sea surface temperature (°C) bias in the Kiel Climate Model (KCM) using all
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years from the 1,000-yr long control run relative to observations (HadISST 1870-2010).
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Figure S2: Spectra of observed monthly-mean Niño3 SST anomalies from observations
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(HadISST, 1870-2010) and the control integration of the KCM (blue) using all 1,000 years.
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B
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Figure S3: Change in SST variability in the Niño3 region as measured by the standard
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deviation (K) as a function of (A) the absolute Niño4 SST (K) and (B) zonal SST contrast (K)
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defined as the difference between the Niño3 and Niño4 SSTs. The circles denote the initial
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states and lines the tendencies. The KCM results (average over the first 30 years) are given by
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the bold red circles. The black crosses denote observations (HadISST1, 1870-2010). The
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different CMIP5 models forced by the RCP8.5 scenario are in given by thin circles and lines.
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Figure S4: Standard deviations (°C) of observed monthly-mean SST anomalies from (A)
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observations (HadISST, 1870-2010) and (B) the control integration of the KCM using all
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1,000 years.
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Figure S5: Annual-mean SST anomalies in the Niño3 region from the CMIP5 models for two
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scenarios: (upper) RCP4.5, (lower) RCP8.5. High-variability models are indicated by legends.
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Figure S6: (A) Precipitation and (B) SAT in Western India (15°N-25°N, 73°E-78°E) for
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“normal” (yellow) and Super El Niños (red). Climatology is given by the black lines.
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B
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Figure S7: (A) The ensemble-mean zonal near-surface (5m) currents (ms-1) along the equator
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during the first 30 years of the global warming integrations. (B) The ensemble-mean
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centennial trend of the near-surface zonal surface currents (ms-1/century) as a function of the
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calendar month and longitude along the equator.
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Figure S8: Ensemble-mean centennial trend of (A) net surface heat flux (Wm-2/century) and
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(B) upper-ocean (0-300 m) heat transport convergence (Wm-2/century).
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Figure S9: (Left) Sensitivity (ms-1/°C) of near-surface (10m) zonal wind to eastern equatorial
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Pacific SST anomalies in the Niño3 region during the global warming integrations; (middle)
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regression [m/(ms-1)] of thermocline depth anomalies upon the Niño4 near-surface (10m)
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zonal wind anomalies; (right) local regressions (°C/100m) between SST and thermocline
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depth (depth of the 20°C-isotherm) anomalies. The upper panels depict the conditions during
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the first 30 years, the lower panels during the last 30 years.
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Figure S10: Annual-mean Niño3 SST anomalies (°C) in two global warming ensembles with
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the KCM. Top: reproduced from Fig. 2 (entitled “KCM new cloud scheme”). Bottom: when
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the stratiform cloud scheme is replaced by another parameterization (entitled “KCM old cloud
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scheme”, see text for details). A third-order polynomial was removed to account for the
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warming trend. The individual ensemble members are shown by different colors. The dotted
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red lines depict the evolution of the ensemble-mean Niño3 SST (°C, right scale).
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Figure S11: Ensemble-mean centennial trend in sea level pressure (SLP, hPa/century) as
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projected by the standard version of the KCM.
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