One of the purported benefits of one of the primary carbon dioxide removal geoengineering schemes, ocean iron fertilization (OIF), has been that it would help to address the issue of ocean acidification, in contrast to solar radiation management approaches, e.g. cloud seeding or sulfur particle injections into the stratosphere. However, a new study by two Stanford researchers, Long Cao & Ken Caldeira, Can Ocean Iron Fertilization Mitigate Ocean Acidification?, 99 Climatic Change 303-311 (2010) (subscription required), suggests that OIF may actually exacerbate the threat posed by ocean acidification. This short reading would be a good addition to a module on geoengineering because it emphasizes the complexity of the impacts of such approaches and potential trade-offs associated with geoengineering.

Among the key take-aways from the study:

1. Even extreme scenarios of OIF would only have a negligible impact on projected declines in pH associated with increased oceanic uptakes of carbon dioxide. “By year 2100 in the simulation with iron fertilization, global surface pH decreases by 0.38 units from a pre-industrial value of 8.18, compared with a decrease of 0.44 units in the scenario without fertilization;”
2. At the same time, iron fertilization increases the amount of carbon sequestered in the ocean interior, accelerating acidification of the deep ocean, especially in the Southern Ocean. This is of particular concern because deep-sea organisms appear to be highly sensitive to even modest changes in pH.

Among the questions that could stimulate class discussion:

1. Even assuming that OIF would not substantially ameliorate ocean acidification, or might even exacerbate it in some regions, might it still make sense to deploy OIF given the serious implications of climate change on the world’s oceans?;
2. What regimes might govern OIF given the potential impacts described in the article? Which would be the most appropriate?