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Many ideas have been proposed for dealing with excess atmospheric carbon dioxide from planting trees to pumping it deep underground. Now there is the proposal to encourage plankton growth in the ocean to "fix" more carbon dioxide than the oceans can naturally handle.

Left on their own, oceans naturally absorb carbon dioxide which then sinks to the ocean floor, and therefore out of the atmosphere.  This process is known as the ocean sink.  Recent research has shown, however, that the oceans may have reached a point where it cannot naturally absorb anymore carbon dioxide.

An American company, Planktos, is proposing to encourage the growth of plankton by distributing tonnes of iron filings into the ocean.  By fertilising plankton growth, more carbon dioxide is absorbed by the plankton, which then sinks to the ocean floor when the plankton dies, much in the same way with trees.

Over 100 scientists met last week at Woods Hole Oceanographic Institute to discuss proposals put forward by Planktos and others.  According to Planktos the scientists agreed that "ocean iron fertilisation projects should proceed to define the role of ocean plankton eco-restoration as an effective tool to slow climate change."

One scientist Dr. Victor Smetecek of the German Alfred Wegner Institute (AWI) said in response to opposing comments:
"In our experiment (the largest most intensively studied to date) we observed that the iron to carbon ratio was 1:50,000 and that 50% of that carbon (as sinking plankton remains) reached 1000 metres within 3 weeks of the iron addition."

Planktos founder Russ George added:
"This is [the] scientific results we've been waiting for AWI to release in public. It confirms that iron micronutrients used to restore plankton blooms create large healthy blooms analogous to natural blooms which rapidly fix CO2 from the surface ocean and sink a major portion as biomass carbon into the deep ocean where it is safely sequestered for centuries or even millennia. Indeed this AWI report is far more optimistic than the ocean models we have used in our science and business plans. This is great news for the planet, and an affirmation of our now clearly conservative business plans. We may actually be able to rapidly reverse the catastrophic decline of ocean ecosystems brought on by fossil fuel CO2."

Not everyone is as optimistic, among them Greenpeace who argued, in a paper presented at the meeting, that:
"such proposals are founded on an incomplete understanding and highly simplified interpretation of current scientific knowledge. They have not taken properly into account the results of the 12 mesoscale iron enrichment scientific studies carried out to date which suggest that the amount of carbon sequestered in this way would be very small, nor the fundamental influence of hydrodynamics and large uncertainties and indeterminacies in ecosystem response which those studies highlight."

They go on to say that:
"Current scientific knowledge strongly indicates that large-scale commercial iron fertilisation would not be an effective climate mitigation strategy. Moreover, there are risks of potentially devastating impacts on marine ecology from such an approach and unpredictable consequences on global climate from the release of climate-active gases.

"Concerns regarding proposals for commercial ocean fertilisation schemes have been voiced by some for many years, though only recently has the issue become more widely debated. In June 2007, the Scientific Groups to the London Convention and London Protocol (Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter) issued a Statement of Concern, setting out their view that large-scale ocean iron fertilisation operations are not justified by current knowledge on both effectiveness in sequestering carbon and potential negative impacts on environment and human health. Similarly, concerns have also been voiced among scientific experts in the field in 2007, to the effect that 'ocean fertilisation will be ineffective and potentially deleterious and should not be used as a strategy for offsetting carbon dioxide emissions.'"

Russ George, President of Planktos, hit back saying:
"This is precisely the scale and careful scientifically designed character of the first of 6 pilot project blooms that our company has worked years to plan and which will begin in a matter of weeks. One shocking element in this field of science and emergency ecorestoration effort on behalf of the planet is the aggressive efforts by radical environmental organisations who are working to misinform the media, public, and government agencies that work in this field is proceeding without proper regulatory and scientific oversight and management that ought to be prohibited. Their case is proven false by the rigorous international, national, and market regulatory processes initiated by the Kyoto Accord and related policies and laws that require scientifically transparent verification and certification via approved methodologies for all carbon offset projects before they can move such carbon offsets into the highly regulated climate change markets."

Planktos is one of a number of private companies and organisations from the USA, Europe, and China with business plans to engage in this field of ocean "stewardship" and climate change mitigation who were invited to attend the WHOI meeting. Among those companies were Climos, Green Sea Ventures, a group from Los Alamos National Laboratory and New Mexico Tech, and the MacDiarmid Institute of China and New Zealand.

Planktos were planning to release up to 100 tons of iron in the Pacific Ocean, 350 miles west of the Galapagos Islands. In May, it was told by the US Environmental Protection Agency that if it were using a US flagged ship, it might need a permit under the Ocean Dumping Act. Planktos consequently postponed the plan, though they may attempt to continue with a ship flagged from another country.