Climate Change
These coral polpys have lost their symbiotic zooxanthellae due to heat stress, causing them to appear white. Photo credit: Emma Hickerson/ Flower Garden Banks National Marine Sanctuary
Climate change and ocean acidification have been identified by many groups as the most important threat to coral reefs on a global basis. In 2007, the Intergovernmental Panel on Climate Change (IPCC) noted that the evidence is now "unequivocal" that the earth's atmosphere and oceans are warming. They concluded that these changes are primarily due to anthropogenic greenhouse gases (i.e.those derived from human activities), especially the accelerating increase in emissions of CO2. 
In 2007, these Acropora corals in the Tumon Bay Marine Preserve in Guam bleached, likely due to higher-than-normal water temperatures caused by global climate change. Photo credit: Dave Burdick
While reducing CO2 and other greenhouse gas emissions is vital to stabilize the climate in the long term, excess CO2 already in the atmosphere has changed and will continue to change global climate throughout the next century. Global ocean temperature has risen by 0.74°C (1.3°F) since the late 19th century causing more frequent and severe bleaching of corals around the world. At the current increasing rate of greenhouse gas emissions, a temperature rise of up to 4.0°C (7.2°F) this century is a distinct possibility. These changes have already had harmful impacts on coral reef ecosystems and will continue to affect coral reef ecosystems globally over the coming century. At the same time, the ocean absorbs approximately one-third of the additional CO2 generated every year by human activities, making the ocean more acidic. The resulting change to ocean chemistry has important consequences for corals and other marine life, especially other important reef builders. Warming seas and ocean acidification are already affecting reefs by causing mass coral bleaching events and slowing the growth of coral skeletons. Bleaching and infectious disease outbreaks are likely to be more frequent and severe as temperatures rise, increasing coral mortality. Climate changes will have other impacts on marine systems such as sea level rise; altered frequency, intensity, and distribution of tropical storms; altered ocean circulation; and others. All of these impacts will combine, often synergistically, to eliminate important ecosystem function and reduce global biodiversity. For more information: NOAA Coral Reef Conservation Program Goals & Objectives 2010-2015 |
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