The New York Times’ climate reporter, Andy Revkin, had an item on his blog, Dot Earth, earlier this week that the for-profit company trying to sell carbon offset credits by fertilizing the ocean with iron has run out of funding to conduct field tests.

I wrote a story back in June about the criticism from environmental groups  levied at Planktos, Inc.’s plans to dump iron dust near the Galapagos Islands. The theory behind ocean fertilization is that iron stimulates the growth of phytoplankton, which absorbs carbon dioxide from the atmosphere as they photosynthesize. When these tiny marine organisms die, they eventually settle to the bottom of the ocean, taking all that carbon they’ve absorbed with them. Generate a large enough plankton bloom, the idea goes, and you can absorb some of that excess carbon dioxide that’s accumulating in the atmosphere and warming up the planet.

But a number of scientists I’ve spoken to, including those at environmental groups such as the WWF, are wary about just how effective ocean iron fertilization is at sequestering carbon. They also point out that there could be uncertain and unintended ecological effects when iron is released in a certain area of the ocean.

In a January issue of the journal Science, a number of international scientists signed onto a warning that it is too early to sell carbon offset credits from ocean iron fertilization (OIF).

The conclusion of the letter states, “This group feels it is premature to sell carbon offsets from 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.”