Ocean Warming 177 3.8 Impacts and efects of ocean warming on coral reefs Scott F. Heron 1 , C. Mark Eakin 1 , Jefrey A. Maynard 2 , Ruben van Hooidonk 3,4 1 NOAA Coral Reef Watch, NESDIS Center for Satellite Applications and Research, College Park, MD 20740, USA 2 SymbioSeas and Marine Applied Research Center, Wilmington NC 28411, USA 3 – NOAA Ocean Chemistry and Ecosystems Division, Atlantic Oceanographic and Meteorological Laboratory, Ocean Chemistry and Ecosystems Division, Miami, FL 33149, USA 4 University of Miami, Cooperative Institute of Marine and Atmospheric Studies, Miami, FL 33149, USA Summary • Despite covering less than 0.1% of the sea loor area, coral reefs provide nearly US$9.8 trillion globally of social, economic and cultural services each year and provide habitat for over 25% of marine ish species. • The rate of warming in coral reef areas has increased from ~0.04°C/decade over the past century to 0.2°C/ decade over recent decades (1985-2012). Across this period, reefs were exposed to prolonged, high temperatures that caused bleaching once every six years. However, within the last three decades, as the planet has warmed the frequency of bleaching stress has increased three-fold. • The latest climate models predict that ocean warming will cause annual coral bleaching for almost all reefs by 2050. They also predict that disease is as likely to be a future cause of coral mortality as coral bleaching. Unabated temperature increases will produce serious consequences for coral reef ecosystems and dependent communities. • The proportion of reefs in which ocean chemistry will allow coral reefs to grow has decreased from 98% (ca. 1780) to 38% (ca. 2006) due to ocean acidiication and continues to drop. • Tropical cyclones can reduce thermal stress but can physically damage reefs. Ocean warming may increase the severity of cyclones. Warming-related coral bleaching has likely reduced the ability of reefs to recover from cyclone damage. • Sea-level rise is predicted to accelerate. Historically reefs have not been able to keep up with rapid sea-level rise, and this is even less likely in the future if ocean warming and acidiication slow reef growth. • Loss of coral reefs would diminish the services these ecosystems provide, such as coastal protection from storm waves, habitat for reef fauna, and tourism. Predictions of ecosystem service losses from ocean warming and acidiication globally reach US$1 trillion/year by 2100. • Reducing atmospheric CO 2 is critical for coral reefs to continue. While reduced emissions will slow ocean warming and acidiication, current CO 2 levels already exceed the 320-350 ppm needed for healthy coral reefs. While this is pursued, enhancing reef resilience through targeted management actions will help reefs to resist and recover from disturbance. Local actions to mitigate climate change impacts may be necessary to preserve reef resources.