Temporary refugia for coral reefs in a warming world

Climate-change impacts on coral reefs are expected to include temperature-induced spatially extensive bleaching events(1). Bleaching causes mortality when temperature stress persists but exposure to bleaching conditions is not expected to be spatially uniform at the regional or global scale(2). Here we show the first maps of global projections of bleaching conditions based on ensembles of IPCC AR5 (ref. 3) models forced with the new Representative Concentration Pathways(4) (RCPs). For the three RCPs with larger CO2 emissions (RCP 4.5, 6.0 and 8.5) the onset of annual bleaching conditions is associated with similar to 510 ppm CO2 equivalent; the median year of all locations is 2040 for the fossil-fuel aggressive RCP 8.5. Spatial patterns in the onset of annual bleaching conditions are similar for each of the RCPs. For RCP 8.5, 26% of reef cells are projected to experience annual bleaching conditions more than 5 years later than the median. Some of these temporary refugia include the western Indian Ocean, Thailand, the southern Great Barrier Reef and central French Polynesia. A reduction in the growth of greenhouse-gas emissions corresponding to the difference between RCP 8.5 and 6.0 delays annual bleaching in similar to 23% of reef cells more than two decades, which might conceivably increase the potential for these reefs to cope with these changes.