Figure 4

Southern Indian Ocean sub-thermocline warming versus aerosol optical depth.

(a) Average temperature of the southern sub-thermocline IO (bottom plot; blue line) versus aerosol optical depth (AOD) at 550 nm averaged over the NH (top plot; black line) from 1950–2100 (based on a 12 CMIP5 MME, including historical and RCP8.5 experiments; see Table S1), (b) scatterplot of the year at which the southern sub-thermocline IO temperature reaches a minimum versus peak NH AOD, for the 12 CMIP5 models, (c) scatterplot of 30-year trend in southern sub-thermocline IO temperature after minimum versus 30-year trend in NH AOD after peak value and (d) scatterplot of 30-year trend in southern sub-thermocline IO temperature from 2006–2035 (i.e., beginning of RCP8.5 experiment) versus 30-year trend in NH AOD from 2006–2035. The number of runs that make up each point are listed in the brackets after model name. The years shown in (a) and (b) and trends in (c) and (d) are based on 11-year running means (to remove year-to-year noise). The line-of-best-fit, R and p-values are also shown. The inter-model spread in (a) is based on the 95% confidence interval. The regression lines in (b) and (c) are statistically significant at the 95% confidence level, whereas the regression line in (d) is significant at the 90% confidence level.