93 / 2023-07-29 20:37:38

Climate Change Increases Global Risk of Coral Bleaching

Marine heatwave, Coral bleacing, Ecological risk

Climate change has led to longer and more intense marine heatwaves (MHWs), which severely affect marine ecosystems. MHWs are likely good indicator of heat stress-induced coral bleaching risk in coral reef ecosystems, but this has rarely been explored. Here we consider two dimensions of MWHs, duration and intensity, to assess the present and future ecological risk across global coral reef areas. From 1982 to 2021, we observed large spatial variations in the mean frequency and maximum intensity of low to medium risk. High frequency and maximum intensity hotspots primarily occurred in the Galapagos Islands, Gulf of California, Persian Gulf, and Red Sea. Differences in the frequency and maximum intensity between shared socioeconomic pathway (SSP) 245 and SSP585 indicated that frequencies decrease at low and medium ecological risk and increase at high risk, whereas the maximum intensity increases at all risk levels. Global average future frequencies increased by 2.2-fold, 13.0-fold, and 75.0-fold under SSP245 and 1.8-fold, 12.7-fold, and 96.0-fold under SSP585 at low, medium, and high risk, respectively, compared with the present frequency. Both the annual mean sea surface temperature and ocean heat content increased across global coral reef areas from 1982–2021. Upper ocean warming drives change in ecological risk assessments. Future increases in the upper ocean heat content and a shallower mixed layer depth may trigger longer and more intense MHWs, substantially increasing the ecological risk. We propose that MHW alerts may be a reliable tool for detecting and predicting coral bleaching risk areas.