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Make Oceans Less Acidic to Speed Carbon Uptake
Emily Gertz, 8 Nov 07

Some of the most profoundly disturbing climate crisis news this year has been the growing evidence that the planet's natural systems for absorbing greenhouse gas out of the atmosphere, particularly the oceans, are beginning to fail. There's simply more carbon dioxide in the atmosphere than these powerful sinks can uptake. (And then there's the Arctic tundra, an ancient sink that's melting and releasing its long-sequestered greenhouse gases back into the atmosphere. Wheeee!)

So it's with great interest that I've been coming across ideas for increasing the capacity of these carbon sinks -- because even if greenhouse gas emissions are cut sharply and fast, there's still many parts per million of crud in the atmosphere that will keep the climate in crises for decades to come, and at typical rates, it will take existing carbon sinks thousands of years to sink it all.

As reported yesterday at Environmental Science and Technology Online, a new study suggests making the ocean less acidic in order to speed up its carbon updake:

"The more acidic the ocean is, the less CO2 it will hold," House explains. On the other hand, alkaline or basic solutions have a strong tendency to absorb CO2. Thus, a more alkaline ocean would pull more of the gas from the air.

Other ideas for increasing ocean CO2 uptake have focused on stimulating phytoplankton growth or increasing alkalinity directly. While House was jogging along the Charles River near Harvard one day, it struck him that he could instead remove acid to achieve the same effect. Eventually, he developed an approach called electrochemical weathering.

Weak acids in water normally dissolve rocks on land over time, forming an alkaline solution that runs into rivers and then the sea. Electrochemical weathering creates a stronger acid to drive much faster reactions. Still at a theoretical stage, the method involves passing an electric current through seawater to separate out chlorine and hydrogen gas, similar to the industrial chloralkali process used to make chlorine gas. The chlorine and hydrogen are then combined in fuel cells to form strong hydrochloric acid. The fuel cells would be housed in an industrial-scale plant that would collect and use the acid to dissolve silicate rocks, which are common worldwide. This would neutralize the acid and the resulting alkaline solution could then be returned to the sea. Overall, the process would help stabilize the oceans' pH, House says, and could benefit corals which are dying from ocean acidification caused by rising CO2 levels.

For profit, plants could sell carbon reduction credits in a cap-and-trade scheme. House says the process could potentially absorb 1 gigaton of CO2 annually. This would require building coastal processing plants equivalent in capacity to about 100 large sewage treatment plants, according to House and his coauthors, Michael Aziz and Daniel Schrag of Harvard University and House's brother Christopher House of Pennsylvania State University.

There are some big impediments to overcome in implementing such a plan. For one, according to ES&T Online, it would cost at least $100 per ton CO2 removed if implemented using currently available technologies. Powering the electrochemical weathering process would itself create CO2, thus reducing the overall impact of the effort. And there might be localized pollution around the plants: "'Around the plant you would get a very basic solution,' which could contain chlorinated byproducts, House says. These byproducts could harm sea life locally."

Still, it's great to see these ideas emerging -- clearly we're going to need a suite of solutions of all sizes and scopes to slow down climate disruption.

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