Fig. 2

Central Pacific relative sea surface temperature (SST) response to the Pinatubo eruption in IPSL-CM5B ensemble simulations. Niño3.4 relative SST (in °C) anomalies, relative to the climatology for the control (black) and Pinatubo ensemble mean (purple) from January of the year of the eruption (labelled year 0) to August 32 months later, for ocean–atmosphere conditions leading to a La Niña, b El Niño and c neutral ENSO state at the end of the eruption year in the unforced control run, based on the warm water volume (WWV) content. The WWV corresponds to the volume of water above the 20 °C isotherm between 5 °N–5 °N and 120 °E–80 °W and is a good precursor of the upcoming ENSO phase in nature⁴. This is also the case in our model as demonstrated by a peak correlation of r = 0.7 when the Niño 3.4 SST index lags the WWV in May by 6 months in the IPSL-CM5B CMIP5 historical simulation⁵⁴. Anomalies are obtained by removing the Niño3.4 relative SST mean seasonal cycle over the 30 years of historical simulations that precede the start of each model ensemble. The colour shading indicates the ensemble spread, based on a 90% confidence interval from two-tailed Welch’s t-test. The vertical dashed line in each panel indicates the date of the eruption