In a joint letter published in the journal Science, the scientists from across the world argue there are still too many uncertainties about the efficiency of OIF in sequestering carbon from the atmosphere.

OIF is one of several marine-based methods which have been proposed for mitigating growing levels of atmospheric carbon dioxide and reducing the impact of climate change.

However, scientists from countries including the US, Japan, India, Germany and the UK warned there could also be unintended ecological impacts which are not yet fully understood.

They raised concerns that private companies are currently planning large-scale iron releases to generate the sale of carbon credits.

Professor Andrew Watson, of the University of East Anglia, was one of the UK signatories of the letter.

He said: “While we do envision the possibility of iron fertilisation as an effective form of carbon offsetting, we believe larger scale experiments are needed to assess the efficiency of this method and to address possible side effects.

“There remain many unknowns and potential negative impacts.”

The joint letter said: “This group feels it is premature to sell carbon offsets from the first generation of commercial-scale OIF experiments unless there is better demonstration that OIF effectively removes CO2, retains that carbon in the ocean for a quantifiable amount of time, and has acceptable and predictable environmental impacts.”

Research since 1993 has shown that releasing iron onto the ocean surface can stimulate the growth of plankton, which use carbon dioxide to create biomass.

Last September, scientists James Lovelock, author of the Gaia Theory, and Chris Rapley, director of the Science Museum, wrote to the journal Nature suggesting the use of vertical pipes in the ocean to achieve the same effect.

Kate Martin

Action inspires action. Stay ahead of the curve with sustainability and energy newsletters from edie