New Geoengineering Scheme Tackles Ocean Acidification, Too

Wired -

A scheme to dump quicklime into the oceans to sequester more carbon in their depths is being revived by a British management consultant with backing from Shell.

First proposed back in the ’90s by Exxon engineer Haroon Kheshgi (.pdf), the idea takes advantage of a series of simple chemical reactions. Limestone, at high temperatures, breaks down into carbon dioxide and quicklime, in a process that produces greenhouse gas. But dump that quicklime in seawater, and it absorbs roughly twice as much CO2 as was released in the first reaction.

The heat required to decompose the limestone will probably come from fossil fuel, generating more CO2, but even so, the sum of the process could be a reduction of the CO2 in the atmosphere.

“If we discover we’ve overshot the amount of CO2 the environment can cope with, the carbon-negative process I’m describing can reduce the amount of carbon dioxide in the atmosphere,” said Tim Kruger, founder of Cquestrate.com, which has drawn seed funding from Shell and bills itself as developing an open source solution to climate change.

Geoengineering projections have shown that it might be possible to stop the warming of the Earth, but the workable ones have had a big problem: the oceans. While schemes like shooting sulfur dioxide into the stratosphere to deflect some of the sun’s energy could cool the Earth, they don’t deal directly with the problem of carbon dioxide in the atmosphere. Regardless of the greenhouse effect, CO2 buildup will lead to ocean acidification, which could wipe out coral reefs and lead to large-scale oceanic ecosystem collapse.

The quicklime scheme is different. It would go right at the heart of the CO2 buildup problem by removing the gas from the air and sequestering it in the world’s oceans. It also makes the oceans more alkaline, directly combating ocean acidification.

Of course, the scale of the project would have to be eye-poppingly large. The early calculations, Kruger told Wired.com, indicate that 56 billion cubic feet of limestone would be required to sequester each gigaton of carbon. Humans put out about 5.5 billion tons of carbon annually by burning fossil fuels, so a limestone offset budget could reach 300 billion cubic feet of limestone per year.