Future Climate Scenarios and Coral Reef Decline
Written by Dr. John Bruno

John Bruno kicks another section of his Reef Science coral series, excerpting a modified version of an article he published last year on the Earth Portal about Coral Reefs and Climate Change. He covers global patterns of coral loss and several of the mechanisms through which anthropogenic climate change is contributing to this trend including coral bleaching, disease and ocean acidification.  Let him know know if there are particular topics you want to hear about.  You can reach him at [email protected]

It is clear that anthropogenic climate change is already negatively impacting the world’s corals and coral reefs.  The threat will almost surely grow over the next several decades as the concentration of atmospheric carbon dioxide increases and ocean warming and acidification accelerate.  Predicting future impacts of climate change on corals and coral reefs is complicated given all the uncertainty about the political response, future technologies, changes in human behavior, the earth climate system and the actual effects on reef inhabitants.  But even conservative forecasts suggest that we could loose coral reef ecosystems by the end of the 21st century.

Corals are thought to require an aragonite saturation of greater than 3.25 to successfully calcify and grow.  Even under the most conservative IPCC climate change scenarios, atmospheric carbon dioxide concentration will increase to 600 ppm over the next 100 years, ocean pH will decrease by 0.1 to 0.3 units and the aragonite saturation in most of the world’s tropical oceans will drop well below the 3.25 threshold.  Field and laboratory experiments and climate models indicate that even more modest acidification will slow coral calcification and growth by nearly 50% by 2050.  Under more extreme scenarios coral skeletons will literally dissolve.  

The 4th IPCC assessment predicted an increase of 1-4 °C in ocean temperature during the next century.  Even the low end of this range could increase summertime high temperatures well beyond the thermal tolerance of most corals and increase the frequency, geographic extent and severity of coral bleaching and mass-mortality events.  Forecast models of increasing ocean temperature and coral bleaching indicate that under most ocean warming scenarios, mass bleaching will happen nearly every summer by 2030. 


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