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Stanford, CA – Much of the carbon dioxide (CO2) emissions from fossil fuel burning is absorbed by the oceans. It is elevating ocean acidity threatening many species, especially those like corals, which use calcium carbonate to make their shells or skeletons. A study published in the March 9, 2007, Geophysical Research Letters* looks at how both increases in CO2 concentrations and increases in temperatures from climate change could affect ocean acidity. It found that regardless of global warming from carbon dioxide, the greenhouse gas is still a threat to life in the world’s oceans.

“Whether you believe in global warming or not, CO2 is going to run havoc in the oceans if unabated,” warned coauthor Ken Caldeira from the Carnegie Institution's Department of Global Ecology. “Temperature increases from climate change affect salinity, circulation, and marine biology. When carbon dioxide dissolves in the ocean, some of it becomes carbonic acid—a corrosive agent, which can eat away shells of important species in the global food chain. Since surface temperature increases affect how carbon is broken down in seawater, we wanted to quantify how the acidity of the water would be affected by temperature increases from CO2 emissions. We found that the pH, or acidity, of the water wasn’t significantly affected regardless of how much warming occurs over the next decades and centuries.”

Today’s average ocean pH value is about 8.1. On the pH scale, lower numbers are more acidic and higher numbers are more basic. The ocean pH has decreased by about 0.1 over the past two centuries. Using an Earth-system model, the scientists found that ocean pH will be reduced by a total of 0.31 units by the end of this century if CO2 emissions continue on their current trajectory to stabilize at atmospheric CO2 concentrations at 1000 parts per million.

The researchers modeled a world with a doubling of CO2 and corresponding temperatures of 0.0° C, 2.5° C, and 4.5° C to the year 2500. Under the latter two scenarios, the pH decreased by .48 and .51 respectively.

“Ocean acidification threatens all marine organisms that use calcium carbonate to make their shells,” said Caldeira. “However even as the planet warms, our study shows that we can help the ecological balance in the oceans by curbing CO2 emissions now by using wind, solar, nuclear power, and other alternative energy sources.”

This work was performed in collaboration with Long Cao and Atul Jain of the University of Illinois, Department of Atmospheric Sciences.

* L. Cao, Caldeira, K., and Jain, A.K., “Effects of carbon dioxide and climate change on ocean acidification and carbonate mineral saturation,” Geophysical Research Letters (GRL) paper 10.1029/2006GL028605, 2007.

The Carnegie Institution of Washington (, a private nonprofit organization, has been a pioneering force in basic scientific research since 1902. It has six research departments: the Geophysical Laboratory and the Department of Terrestrial Magnetism, both located in Washington, D.C.; The Observatories, in Pasadena, California, and Chile; the Department of Plant Biology and the Department of Global Ecology, in Stanford, California; and the Department of Embryology, in Baltimore, Maryland.

News Topic: 
Climate Change