Concerns over carbon credit scheme to fertilise the oceans

US company, Planktos, is preparing to fertilise the eastern Pacific with powdered iron ore to create an artificial algal bloom in an attempt to sequester carbon. It hopes to use the trial to gain accreditation for carbon credits, but critics have called the plan reckless.

Planktos plans six trials, the first of which will fertilise up to 10,000 square kilometres of the Pacific Ocean off the Galapagos Islands in June. The aim is to stimulate plankton growth and accelerate carbon dioxide uptake.

Russ George, Planktos’s chief executive said the firm will monitor the bloom throughout its life cycle, which could take up to six months. Ship-based sampling and satellite imagery will be used to collect data on the bloom’s composition and behaviour and monitor its effects on local biodiversity.

The idea is not new. Since it was first suggested ten years, several small-scale trials have proved that iron deficiency can limit algal populations. But researchers cannot say how much of the carbon absorbed by algae makes it to the ocean floor and is sequestered and how much returns to the atmosphere.

A study of a natural 45,000km2 algal bloom in an iron-rich region of the Southern Ocean, published in Nature, showed that about 30% of the carbon fixed reached the lower ocean. This is 10 to 100 times more carbon sequestered per unit of iron than seen in smaller studies.1However, the UN’s Intergovernmental Panel on Climate Change’s recent report on mitigation measures is dismissive of the concept (ENDS Report 388, pp 10-11 ). "Options, such as ocean fertilisation… remain largely speculative and unproven, and with the risk of unknown side effects," it says. "Reliable cost estimates for these options have not been published."

But this has not deterred Mr George. That the IPCC acknowledged the method at all was encouraging, he said, and justified his company’s trials.

Planktos already sells voluntary carbon sequestration credits from tree planting and ocean fertilisation for $5/ton on its website. It claims the ocean fertilisation credits are "verifiable" but Mr George admits they have not yet been approved by the Kyoto Protocol’s clean development mechanism (CDM) or any other government trading scheme. He said he hopes to use the data from the trials to make a case for registering the method under the CDM.

Nonetheless, Planktos’ plans have come under fire. Canadian environment oganisation ETC Group has labelled it a "maverick" company of "geoengineering fanatics" and Greenpeace has accused it of recklessness.

"Climate change should be tackled by reducing emissions, not by altering ocean ecosystems," said Paul Johnston, head of the NGO’s science unit.

Mr George believed the discontent has arisen because the trials are being done by a profit-making organisation. He accuses the firm’s critics of underhand tactics, including attacks on its computer servers. However, academics have also raised concerns.

Richard Lampitt, a researcher at the National Oceanography Centre in Southampton, is among those who have spoken out: "Seeding the oceans with iron filings has a carbon cost," he said. "We should proceed with great care before making an assault on these remote and fragile ecosystems."

He also feared that the plankton could release methane - a greenhouse gas 20 times more potent than CO2.

The authors of the natural bloom study are also sceptical. The effects of ocean fertilisation depend on several interlinked factors including the way iron is added and the availability of other nutrients.

Their results "should not be taken as an indication that controversial geoengineering CO2 mitigation proposals will be able to obtain high [sequestration] efficiencies," they cautioned.

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