I hadn't seen any references to ocean sequestration of carbon dioxide in some time, and then within a week or so two different colleagues mentioned a company called Planktos to me. As you might guess from the name, they are pursuing a method of sequestration that involves seeding the ocean to stimulate plankton, which absorb CO2 via photosynthesis, eventually resulting in the sequestered carbon sinking to the sea bottom. Here's what I wrote about this idea in October 2004 (with some of the links updated):
A week or so ago the BBC evening news (on PBS) included a report on the possibility of sudden, rapid climate change as a result of accumulating carbon dioxide and other greenhouse gases in the atmosphere. The prospect of the climate changing dramatically within a decade or two--which has apparently happened in the geological past--reminded me of a novel strategy that might be able to counter such a development. It's called "ocean sequestration".
I've mentioned carbon sequestration before. Most of the work in this area currently focuses on recovering carbon dioxide from smokestacks, compressing it, and pumping it into disused oil or gas wells or other underground sinks. The technique looks very promising, but it is essentially industrial in nature, requiring substantial investment, infrastructure and expense, making it hard to deploy quickly or on a large scale.
Ocean sequestration differs in several important ways. First, it would tie up carbon using biological processes, by stimulating plankton growth and effectively capturing the carbon in the pelagic food chain and its solid wastes. As a result, it does not require large amounts of capital or infrastructure. Second, it removes CO2 directly from the atmosphere, rather than from a smokestack, and appears to be easily scalable, making it possible to tackle the much larger sequestration goals that sudden climate change would require. In other words, the rate of sequestration might exceed the total global rate of CO2 emissions. If the world were experiencing a runaway greenhouse effect, we would need a technique that could cut the absolute quantity of CO2 in the atmosphere--rather than just reducing the rate at which it is increasing--in order to restore equilibrium.
Although ocean sequestration is still in early stages of research, it has come in for serious criticism for its possible impact on ocean ecosystems. The jury is still out on these concerns, and it could turn out that they are negative enough to prevent this technique from becoming a standard approach for managing greenhouse gas emissions. But if faced with a choice between a rapidly changing climate--with its unpredictable effects not only on ecosystems but on human survivability--I'd like to think that we had at least one "Hail Mary" pass like this waiting in our playbook, just in case.