The parties to the London Convention, the international treaty governing ocean dumping, have agreed that large-scale ocean 'fertilization' is currently not justified given gaps in scientific knowledge.

Adding iron, phosphate or urea can stimulate plankton growth in nutrient-poor parts of the ocean ? thereby sucking down carbon dioxide from the atmosphere and potentially helping to combat climate change. But critics warn that the ecological impact is poorly understood, and at its meeting in London last week, the convention endorsed concerns issued in June by its scientific advisory group.

Environmentalists last week also raised concerns over an Australian company's plan to test its carbon-sequestration technology in Philippine waters. Ocean Nourishment Corporation (ONC) of Pyrmont, New South Wales, is currently in discussions with Philippine authorities over dumping 500 tonnes of dissolved urea, a nitrogen-based fertilizer, in the Sulu Sea between Borneo and the Philippines.