Fig. 5: Projected future bleaching scenarios.

Future projections of accumulated heat stress (greyscale upper panels; DHW—degree heating weeks) and mass coral bleaching conditions (lower panels) are shown for four shared socioeconomic pathways (SSP) with Paris Agreement (a, SSP1–2.6), middle-of-the-road (b, SSP2–4.5), middle-high (c, SSP3–7.0), and worst-case (d, SSP5–8.5) emissions scenarios. Ensemble projections are based on downscaled sea surface temperatures from 17 Global Circulation Models (GCMs). High-frequency bleaching is considered to occur when at least two bleaching events (i.e., DHW events >8 °C-weeks) are projected to occur in any given decade. Projections of DHW (upper panels, greyscale shading) and bleaching (lower panels, lines) are shown for four simulated increases in thermal tolerance: 0.0, 0.1, 0.2, and 0.3 °C/decade (coloured lines). A fixed thermal tolerance (yellow dashed line) is the null hypothesis, the most-likely historic rate of change in thermal tolerance according to the most parsimonious model is 0.1 °C/decade (bold line), and more rapid shifts beyond the most-likely historic rate are also shown (purple and blue dashed lines). DHW is displayed as an ensemble mean across all GCMs, while bleaching trajectories are shown as the ensemble mean ± SE. Source data are provided as a Source Data file.