Extended Data Fig. 6: Projected change in pIOD frequency.

a, Moderate and b, strong pIOD using a threshold of M-index>1.25 s.d. and S-index>1.5 s.d., respectively. Shown is the comparison of frequency (events per 100 years) in the present-day (1900–1999) and future (2000–2099) climate in the 20 selected models, that is, with an α greater than 50% of the observed value. A total of 17 out of the 20 models (85%) simulate a decreased frequency in moderate pIOD events, with a statistically significant decrease of 52% in the multi-model mean, from 9.60 events per 100 years in the present-day (blue bars) to 4.65 events per 100 years (red bars) in the future climate. By contrast, a total of 16 out of the 20 models (80%) simulate an increased frequency in strong pIOD events, with a statistically significant increase of 66% in the multi-model average, from 7.5 events per 100 years in the present-day (blue bars) to 12.45 events per 100 years (red bars) in the future climate. Models that simulate an opposite change to the multi-model mean are indicated by green circles. c, Same as a, but using a threshold of M-index>1.5 s.d. A total of 18 out of the 20 selected models (90%) simulate a decreased frequency in moderate pIOD events, with a statistically significant decrease of 60% in the multi-model ensemble mean. d, Same as b, but using a threshold of S-index>1 s.d. A total of 18 out of the 20 models (90%) simulate an increased frequency in strong pIOD, with a statistically significant increase of 44% in the multi-model ensemble mean. Models from CMIP6 are indicated in purple.