BBC: Fertilising the oceans with iron to absorb carbon dioxide could increase concentrations of a chemical that can kill marine mammals, a study has found. Iron stimulates growth of marine algae that absorb CO2 from the air, and has been touted as a “climate fix”. Now researchers have shown that the algae increase production of a nerve poison that can kill mammals and birds. Writing in Proceedings of the National Academy of Sciences, they say this raises “serious concern” …