Fig. 2: Impact of tropical Indian Ocean warming on North American GPP.

a Composite difference in observed July–August GPP from NIR (gC m−2 month−1) between TIO warming years (>+0.5 s.d.) and cooling years (<−0.5 s.d.), after removing the effect of Niño 3.4 variability, for 1982–2018. Dotted areas indicate regions significant at the 95% confidence level based on a Student’s t-test. b Composite difference in July–August GPP between TIO + 0.5 °C and TIO − 0.5 °C model experiments, after removing the effect of Niño 3.4 index. c Statistics of simulated North American GPP anomalies during TIO warming and cooling experiments. Bars indicate ensemble mean GPP, and open circles show values from individual ensemble members.