Fig. 1

Observed and CMIP5 relative sea surface temperature (SST) response to the five main eruptions with stratospheric aerosol injection during 1870–2010. a Evolution of the composited Niño3.4 (5 °S–5 °N, 170 °W–120 °W) relative SST anomalies (SSTA) over a 2-year period following the five largest volcanic eruptions during 1870–2010 in HadISST observations⁴⁶ (black line). The red dots denote when the 5 events (colour lines) have anomalies of the same sign. An arrow indicates the dates and relative magnitude (based on Aerosol Optical Depth provided by Gao et al.⁵¹) of the selected eruptions. b Same as a but shown as a longitude-time section. The black rectangle denotes the Niño3.4 region during October–November–December. Stippling highlights times and locations where the 5 eruptions display anomalies of the same sign and the contour corresponds to the 90% significance level of this anomaly according to a two-tailed Student’s t-test. The composited anomalies are relative to the preceding 5-year climatology. c Anomalous percentage of CMIP5 historical simulation members with an El Niño occurrence for the entire historical period (136 years). The anomalous percentage is given relative to the climatological rate over the entire period. El Niño events are defined as Niño3.4 positive relative SST anomalies exceeding 1/2 standard deviation. The vertical coloured lines localize each eruption date and the pink shading a period of 2 years following the eruption. Continuous and dashed horizontal lines indicate one and two standard deviations respectively. The red shading outlines one standard deviation from the mean of the ensemble