Iron limitation of phytoplankton growth in extensive ocean areas has been conclusively demonstrated by small-scale, direct iron additions to surface waters. No further addition experiments are needed to establish that. However, proposals to expand ocean iron fertilization (OIF) to massive scales for removal of carbon dioxide from the atmosphere are environmentally short-sighted. Commercial interests hoping to collect payments for carbon credits by deep-sea sequestration of OIF-stimulated organic matter are promoting the scheme despite (1) convincing evidence that it won’t work at a significant rate relative to nearly certain ongoing rates of carbon burning, (2) its explicit intent is to disrupt the normal function of globe-girdling marine ecosystems and (3) strong focusing of organic matter inputs to the sea in space and time, regionally enhancing deep (and not so deep) oxygen depletion. No OIF experiments small enough to be safely mixed away will also be large enough to show the impacts of persistent OIF at scales sufficient to remove enough CO2 even to measure against ongoing atmospheric increases (the upward thrust of the Keeling curve). Those “commercial” scales entail risks to ocean ecosystems as great as those of warming itself.