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Ocean Warming and Coral Bleaching in Biodiversity Hotspots
Axel Timmermann (IPRC), Laurie Menviel (U. of Hawaii),
Lizzie McLeod (Nature Conservancy), Zhengyu Liu (U. of Wisconsin)
Corals bleach when sea surface temperature anomalies rise for several weeks by more than 1ºC over the corals’ usual
temperature range. To identify which coral reef regions are most likely to experience thermal stress and mortality,
simulations were analyzed from an ensemble of 20 state-of-the art climate models forced by increasing atmospheric CO2
through the 21st Century. Panel a shows the ensemble mean rise in SST from 2000–2007 to 2090–2100. The projected future
warming was largest around the equator; in the off-equatorial regions, stronger winds, changes in the air–sea specific
humidity gradient, and increased low-level clouds dampened the warming effect of CO2. Panel b shows the time horizon for
simulated SST to permanently exceed the present-day estimates of bleaching thresholds. Corals in the equatorial warm pool
(the Coral Triangle and parts of Melanesia) are most vulnerable to global warming: they are already more sensitive to
temperature fluctuations and the highest temperature rise is predicted around the equator. According to the models, by
2050 temperatures in the warm pool will permanently exceed the current bleaching threshold, a phenomenon that then
spreads poleward, reaching the Hawaiian Isles around 2080.