A Harvard graduate student has a provocative suggestion for slowing global warming: Increase the ocean's natural capacity for absorbing carbon dioxide from the air, in part by speeding up the natural process of weathering rocks.
In a paper published in the current issue of Environmental Science and Technology, geology student Kurt Zenz House, along with several colleagues, said that about 15 percent of global carbon emissions each year could be removed through a two-step process.
"The idea of neutralizing carbon dioxide has been around a while, and it's a good one," said University of Chicago geophysicist David Archer. "The cool idea here is using chemical engineering to come up with a practical way of doing that," Archer says.
His proposal is based on a basic chemical theory: seawater that is more alkaline can absorb more carbon dioxide.
House suggests building 100 water treatment plants in remote places such as volcanic islands of the South Pacific or the far reaches of the Alaskan archipelago. The plants would electrochemically combine the hydrogen in seawater with the chloride in salt to produce hydrochloric acid. The reaction removes the acid from the water, making it more alkaline when it is returned it to the sea.
The hydrochloric acid would then be sprayed on nearby rocks. Just as rain weatherizes rocks, the acid would react with alkaline minerals in the rocks and be neutralized before flowing back into the ocean.
Other scientists have proposed increasing the ocean's alkalinity by mining minerals such as magnesium carbonate and dissolving them into ocean water, House says. "It's an old idea, but the problem with it is there isn't a large, readily available source of alkalinity. Most minerals also have carbon in them, which doesn't help" combat global warming, he said.
His proposal turns that idea on its head: rather than add alkalinity to the ocean, he suggests removing acid.
House acknowledges that his process is not without some risk. For one, he hasn't yet assessed how a plant spewing out highly alkaline seawater would affect local marine life. It's possible that the process could produce compounds called halogenated organics, which can cause the destruction of the ozone layer - a problem House admits would be a show-stopper.
And it would likely carry a hefty price tag, he says.
In fact, House says he looks at this process as more of a safety measure to rely on if we aren't successful in curbing carbon emissions in other ways, such as through increased energy efficiency or more reliance on renewable resources.
"It's technically feasible but it's not cheap," House cautioned. "It's much cheaper to start making our energy switch now."
