Coral temperature reconstruction: validation. (a) Composite coral temperature reconstruction for the western tropical Indian Ocean. The thin blue line are the bimonthly values, the thick magenta line is a 61-point moving average. (b) Coral cores included in the composite record. Magenta line: coral δ18O records from the Seychelles10,11, Green line: coral Sr/Ca records from the Chagos Archipelago (this study and12,13). (c) Comparison of the coral derived temperatures (5 and 3 core averages) with a composite record computed from local air temperature (Mahe, Seychelles, and Diego Garcia, Chagos; see supplementary material) and local OI SST (1° × 1° grid, available since 198218). All records have been centered by subtracting their mean. (OI SST has been centered relative to the mean of the air temperature between 1982 and 1998) (d) Scatter plot of coral derived temperatures vs. the local air temperature/OI SST composite. For the 5-core reconstruction, the correlation is r = 0.84 (significant at the 1% level assuming 38 degrees of freedom, n = 40) and the slope of the linear regression is not significantly different from 1.