Some scientists say iron can combat climate change. The idea is that if you seed the oceans with iron, it will encourage phytoplankton blooms, one of the biggest carbon sinks on the planet. According to the New York Times, that could be a double-edged sword.

Phytoplankton removes carbon dioxide from the atmosphere through photosynthesis. When it dies and sinks, it essentially sequesters the carbon deep in the ocean. The idea is popular in some circles, but most scientists have remained skeptical because of concerns about large-scale manipulation of ocean ecosystems.

But is such oceanic iron seeding a bad idea or is it a not-so-crazy idea for fighting climate change?

It’s true that it would be an effective means of carbon sequestration, but a study in The Proceedings of the National Academy of Sciences points out a newly discovered risk. The NY Times’ article says, "by promoting the growth of certain organisms, iron enrichment may result in the harmful production of a neurotoxin."

Charles G. Trick and his colleagues from the University of Western Ontario conducted the study. They studied several species of diatoms and the genus Pseudonitzschia and found that these organisms produce domoic acid. The plankton use this acid to fuel growth, but it is also highly toxic to many marine mammals and humans.

In fact, when large blooms of Pseudonitzschia occurred in coastal waters, the toxin led to the poisoning of sea lions via tainted shellfish. Studies suggest that when such phytoplankton blooms occur in mid-ocean waters, they do not produce the toxin.

According to the NY Times’ article, "Dr. Trick said his team’s work suggested that the earlier studies were flawed. Pseudonitzschia collected in mid-ocean and subjected to shipboard experiments produced plenty of domoic acid. 'We found there is a lot of toxin out there,' he said. 'If we were to seed with iron, the amount of toxin would go up.’”