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PRI's Environmental News Magazine

Acid Oceans

Air Date: Week of November 16, 2007

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Ken Caldeira (Courtesy of the Carnegie Institution)

More carbon in the ocean means a lower pH, moving the oceans towards the acidic range of the pH scale. This causes some major problems for marine creatures and ecosystems. Host Steve Curwood talks with Dr. Ken Caldeira, an oceanographer of Carnegie Institution at Stanford University to find out what the impact of CO2 is underwater.


CURWOOD: As the atmosphere and oceans reach saturation point for carbon dioxide, things start to get a little sour—acidic actually. That’s right, as greenhouse gases increase, the pH of the ocean changes. Already measurements show the oceans acidifying faster than scientists were expecting.
On the line is Dr. Ken Caldeira, a chemical oceanographer with the Carnegie Institution at Stanford University. Now, Dr. Caldeira, you’ve been studying acid levels in the ocean for a long time. In fact, that was the subject of your PhD dissertation. Can you tell me about that?

CALDEIRA: About 65 million years ago, meteorites slammed into the Yucatan Peninsula and as a result, all kinds of carbon dioxide and sulfuric acid was given off. And that rained down onto the ocean and acidified the surface ocean. And at that time coral reefs and other marine ecosystems that depended on making shells or skeletons out of calcium carbonate disappeared. It took them hundreds of thousands to millions of years to come back.

CURWOOD: So, what’s going on here? As we put more and more CO2 into the atmosphere, more and more is going into the ocean, and what’s it doing to the organisms there?

Ken Caldeira (Courtesy of the Carnegie Institution)

CALDEIRA: If we continue our present trends of emitting carbon dioxide into the atmosphere somewhere, several decades from now, the shells or skeletons of submarine organisms will start to dissolve. There’s a kind of sea snail at the base of the food chain in the southern ocean known as ‘terrapods’ and experiences in laboratory settings have shown that with CO2 concentrations expected in just a few decades, their shells will start to dissolve. We did studies on looking at the chemistry of where coral reefs are and what kind of water coral reefs grow in. And essentially there will be none of this type of water left in say, 50 years or so, if we continue with present trends of carbon dioxide emissions.

And, as the ocean surface warms, less oxygen is able to dissolve into the ocean, and so some marine organisms may be at least threatened with suffocation by a twin whammy of having warmer water with less oxygen in it and high CO2 levels so their blood is less able to transport oxygen to their muscles. So, we are changing the oceans in ways that it hasn’t been changed in many millions of years and it’s uncertain how marine organisms will react to all this.

CURWOOD: Can you just briefly tell me how you go from a molecule of carbon dioxide in the atmosphere to say, a mollusk not being able to have a shell?
CALDEIRA: What happens when carbon dioxide is absorbed by sea water is that CO2 molecule reacts with an H2O molecule, the water molecule, and in this reaction, it gives off a proton or a hydrogen ion, and that’s what we measure when we measure pH or talk about acidity. And that hydrogen ion that’s given off attacks what’s called a carbonate ion, and that’s what the marine organisms use to build their shells. Calcium carbonate is a calcium ion plus a carbon ion, and so CO2 is absorbed by seawater, it reacts with the seawater and gives a proton and that proton attacks the building blocks that marine organisms need to build their shells and skeletons.

CURWOOD: Intergovernmental Panel on Climate Change—it’s got a synthesis report of all the research that it’s done and how close is that to what you are observing in the change of carbon dioxide in the planet?

CALDEIRA: Atmospheric CO2 emissions and atmospheric CO2 concentrations are both increasing more rapidly than even the most pessimistic of the IPCC scenarios generated just a few years ago. Nobody really saw the rate of development of coal in China and also in India. Also, the high price of oil is pushing people to use less oil and more coal and all of those factors are really increasing CO2 emissions and atmospheric CO2 concentrations beyond what anybody had foreseen.

CURWOOD: So the question then comes: what about geo-engineering? What about something to speed up this process of rebalancing the oceans that we’ve put out of whack?

CALDEIRA: We’ve looked at taking limestone and dissolving it at power plants and so on and we might be able to save certain bays as some kind of marine sanctuary and to have a kind of Disney world of the ocean that could be visible in the future, but the scale at which you would need to counteract the effect all across the ocean would be really huge. It would be taking hundreds of cubic miles of limestone every couple of years. The main thing is—what we would need to do to save the oceans is about the same size as our whole energy system, so it’s easier just to change our energy system.

CURWOOD: Ken Caldeira is a chemical oceanographer with the Carnegie Institution at Stanford University. Dr. Caldeira, thank you so much.

CALDEIRA: Thank you.



Ken Caldeira's chapter on CO2 absorption by the oceans in the IPCC's 2005 global report

To read a report Dr. Caldeira presented to the National Academy on CO2 and Coral Reefs click here.


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