Needing iron ... there were hopes plankton could tackle warming.
COULD the tiny plankton that spends its days bobbing in the chill waters of the Southern Ocean hold the key to solving climate change? Actually, no.
New research from Sydney University appears to have scotched ambitious plans to fertilise the ocean and spawn huge plankton blooms.
The theory was that by scattering iron dust from boats, plankton would multiply and suck up carbon dioxide from the air before carrying it down to the ocean depths, where it can no longer contribute to global warming.
It has led to some bold experiments such as that carried out in July by Californian businessman Russ George.
Mr George - a former chief executive of a company that promoted geoengineering technology - dumped 100 tonnes of iron sulfate off the coast of Canada and apparently created an algal bloom of up to 10,000 square kilometres. The experiment was condemned by environmental groups, which dubbed Mr George a ''rogue geoengineer'', and lawyers who alleged it had breached international conventions.
But research by Sydney University and the Sydney Institute of Marine Science found large-scale iron fertilisation would be a waste of time and money in almost all conditions.
''It blows iron fertilisation out of the water,'' said Daniel Harrison, whose paper on the subject is published in the International Journal of Global Warming. ''It is possible to do iron fertilisation efficiently but the perfect conditions you would need are so rare that it would be a very limited contribution to the problem.''
By analysing all known iron fertilisation experiments, and calibrating them with computer models estimating the ebb and flow of the oceans, he established storing carbon dioxide in the ocean would cost about $433 per tonne. This compares unfavourably with the $23 per tonne Australian carbon price.
The process works because iron is a nutrient plankton needs in order to grow. When they die, some sink so deep the carbon dioxide they harvest from the atmosphere is removed from the Earth's carbon cycle for over 100 years.
But Mr Harrison's work shows fertilising a square kilometre of the Southern Ocean would only store about 10 kilograms of carbon dioxide - about as much as a car would emit from burning four litres of petrol.