Climate refugia on the Great Barrier Reef fail when global warming exceeds 3°C

Increases in the magnitude, frequency, and duration of warm seawater temperatures are causing mass coral mortality events across the globe. Although, even during the most extensive bleaching events, some reefs escape exposure to severe stress, constituting potential refugia. Here, we identify present‐day climate refugia on the Great Barrier Reef (GBR) and project their persistence into the future. To do this, we apply semi‐dynamic downscaling to an ensemble of climate projections released for the IPCC's recent sixth Assessment Report. We find that GBR locations experiencing the least thermal stress over the past 20 years have done so because of their oceanographic circumstance, which implies that longer‐term persistence of climate refugia is feasible. Specifically, tidal and wind mixing of warm water away from the sea surface appears to provide relief from warming. However, on average this relative advantage only persists until global warming exceeds ~3°C. Increasing global average temperatures are driving mass coral mortality events around the world. Although, there are some reefs that escape the warm exposure, deemed as a potential refugia. We apply a unique method to improve coarse resolution climate projections over the Great Barrier Reef, isolating the locations that have experienced the least amount of thermal stress over the past 20 years. Wind and tidal mixing enabled the persistence of climate refugia in these locations. However, this advantage only persists until global average warming exceeds ~3°C.