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The third and in many respects the greatest concern in the longer term, is that global change is causing the world's oceans to become more acidic. By burning immense amounts of fossil fuels, humans, particularly North Americans, are rapidly increasing the concentration of carbon dioxide (CO2) in the atmosphere (by roughly 30% to date). A quarter of the CO2 produced by the burning of fossil fuels enters the ocean and reacts with water to form carbonic acid, acidifying the ocean. We have already lowered the pH of the ocean by about 0.1 unit which makes it more difficult and energetically costly for corals to secrete their calcium carbonate skeleton.

Several experiments have demonstrated than even modest decreases in pH can slow coral growth, which will cause and compound a number of other problems. For example, it will reduce the ability of corals to compete with other species like sponges and seaweeds and to keep up with higher rates of sea level rise (due mainly to the thermal expansion of the ocean, but also to the melting of polar glaciers and ice caps). Coral populations might also recover more slowly from other climate change-related stressors like bleaching and infectious disease or from natural disturbances and mortality agents like storms or predation.

Literature cited

Hoegh-Guldberg, O. et al. 2007. Coral reefs under rapid climate change and ocean acidification. Science 318:1737-1742.

Further reading

Bruno, J.F. and O. Hoegh-Guldberg, 2009. Declining calcification on the Great Barrier Reef. Climate Shifts.

Pew Center on Global Climate Change. Coral Reefs and Global Climate Change

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