Coral bleaching projections for the Great Barrier Reef throughout the 21st century

Australia's Great Barrier Reef (GBR) is emblematic of the beauty of coral reefs and the perils they face. Of primary concern is the increasing frequency of mass coral bleaching events, when environmental stressors disrupt the symbiosis between coral host and algal energy source on a major scale. Here, we used four decades of observed environmental variability and bleaching events to calibrate predictors of large-scale bleaching on the GBR, which included sea surface temperature, ocean currents, and light stress. Future bleaching projections were developed from a suite of models in the Coupled Model Intercomparison Project (CMIP6), covering ranges of future emissions scenarios and bleaching sensitivities. For return times between bleaching events to stabilize at three or more years—giving corals any chance of reproducing between bleaching—requires an optimistic scenario of coral sensitivity and either a sustainable future (SSP1) or a "middle of the road" emissions future (SSP2).