Extended Data Fig. 4: Simulated changes in different MHW characteristics exceeding the preindustrial 99th percentile.

The data were obtained from a 10-member ensemble simulation with NCAR-DOE CESM³⁴. a–d, The probability ratio (a), annual mean duration (b), maximum annual intensity (c) and annual cumulative mean intensity (d) of MHWs. The black lines show the individual ensemble members. The red line in a shows the probability ratio versus global warming for a reference period that is defined as the 99th percentile over the 2007–2026 period, obtained using all ten ensemble members. The ensemble members are initialized from different starting points (ocean, sea ice, land and atmosphere) in the preindustrial control simulation. The simulations follow the RCP 8.5 scenario over the 21st century. The time series are smoothed with a 20-year running mean.