Fig. 3: The return period of record-breaking annual SST events increases with the size of the margin by which they exceed previous records.

a, Record-breaking annual (April–March) global (60° S–60° N) SST events and the margin (ΔSST) by which they exceeded previous records based on 190 climate model simulations from CMIP6 (blue dots) (Extended Data Table 1), 30 members of the GFDL-ESM2M-LE^41,42 (orange dots), 50 members from the CESM2-LE^43,44 (green dots), and SST observation-based estimates from NOAA OISST V2.1¹ (black crosses). b, Return periods of record-breaking events of a given magnitude (binned in regular bins of 0.025 °C) calculated based on their occurrence in a for the ensembles of CMIP6 (blue), GFDL-ESM2M (orange) and CESM2 (green). The return periods indicate the return period for a record-breaking event of that magnitude and not of an event that is equal or larger than the magnitude of that bin. Return periods for ΔSSTs of more than 0.275 °C are not simulated by the large ensembles of GFDL-ESM2M and CESM2, possibly owing to their relatively small sample size (1,230 years between 2000 and 2040 for the GFDL-ESM2M-LE and 2,050 years for the CESM2-LE). Observed record-breaking events, corresponding to the crosses in a, are shown as dotted black vertical lines.