In their letter to journal Environmental Science and Technology, the scientists say that the decision by Norwegian Minister Environment Borge Brende to halt the project was brought on by pressure groups.

A permit was originally granted to researchers from 15 institutions to carry out a study of the physical and biological changes following injection of carbon dioxide into the ocean. Two remote-controlled units would have monitored the fate of liquid CO2 discharged into the Norwegian Sea at a depth of 800 metres, says the letter.

The plan was to release 5 tons of CO2 over a week as part of a small-scale pilot study to establish whether Gigatons of CO2 could eventually be pumped into the ocean. But the Norwegian minister now says that more debate is needed before action can be taken.

The scientists argue that action is needed urgently to explore as many mitigation options as possible. Ocean carbon sequestration must be tested because it is the biggest mitigation option available today, says the letter. Through the natural carbon cycle, say the scientists, the ocean annually sequesters about 7 Gigatons of industrial CO2, about a third of the world’s emissions.

A separate international project is assessing the feasibility of storing CO2 in layers of porous sandstone (see related story).

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