Mar 23, 2007
Carbon dioxide threatens oceans even without warming
Rising carbon dioxide levels are a threat to marine biodiversity regardless of whether global warming turns out to be strong or weak. So says a recent study by scientists at the University of Illinois and Carnegie Institution, US.
"Ocean chemical effects of carbon dioxide threaten coral reefs and many other organisms that make their shells or skeletons out of calcium carbonate," Ken Caldeira of the Carnegie Institution told environmentalresearchweb. "This threat is there regardless of whether the Earth warms rapidly or not at all. It is unknown just how the collapse of key species will affect the biodiversity of the oceans, but the sign is clear - we will be losing many species in the ocean if we do not rapidly curtail our carbon dioxide emissions."
When carbon dioxide is absorbed by seawater it increases the concentration of hydrogen ions, which raises acidity. In turn, some of the additional hydrogen ions react with carbonate ions, decreasing their availability. Many marine organisms use carbonate ions to build up skeletons or protective shells so a reduction in carbonate ion levels could highly detrimental.
The researchers used an Earth-system model dubbed the Integrated Science Assessment Model (ISAM) and developed by Atul Jain and Long Cao of the University of Illinois.
"I was involved in earlier studies on ocean acidification, but these studies looked only at the chemical effects of carbon dioxide in the ocean and did not include the effects of climate change," said Caldeira. "We used a model of the Earth that includes representations of the land, atmosphere, and ocean, considering both climate and chemical effects of carbon dioxide."
According to Jain, before the study there was speculation in the academic community that climate change would have a big impact on ocean acidity. "We found no such impact," he said.
"Warmer water directly reduces the ocean pH due to temperature effect on the reaction rate in the carbonate system," said Jain. "At the same time, warmer water also absorbs less carbon dioxide, which makes the ocean less acidic. These two climate effects balance each other, which results in negligible net climate effect on ocean pH."
The pH of the ocean surface has decreased by about 0.1 over the last 200 years, as a result of carbon dioxide absorption. ISAM predicts that ocean pH will decline a total of 0.31 by 2100 if carbon dioxide emissions continue on a trajectory to stabilize at 1000 parts per million.
The study shows that even if geoengineering solutions such as reflective balloons in the stratosphere or parasols in space were able to reduce temperatures on earth, this would only remove one of the problems caused by increased carbon dioxide levels - ocean acidification would still occur, damaging marine ecosystems.
"I have been working to communicate our research results by visiting Congress and discussing this issue with Congressional staffers and a few Congressmen such as Representatives Inslee and Gilchrest," said Caldeira. "Our next step is to perform calculations to show how much we would need to reduce emissions to protect our marine ecosystems."
The researchers reported their work in Geophysical Research Letters.
About the author
Liz Kalaugher is editor of environmentalresearchweb.