Feasibility of ocean fertilization and its impact on future atmospheric CO2 levels

Iron fertilization of macronutrient‐rich but biologically unproductive ocean waters has been proposed for sequestering anthropogenic carbon dioxide (CO2). The first carbon export measurements in the Southern Ocean (SO) during the recent SO‐Iron Experiment (SOFeX) yielded ∼900 t C exported per 1.26 t Fe added. This allows the first realistic, data‐based feasibility assessment of large‐scale iron fertilization and corresponding future atmospheric CO2 prognosis. Using various carbon cycle models, we find that if 20% of the world's surface ocean were fertilized 15 times per year until year 2100, it would reduce atmospheric CO2 by ≲15 ppmv at an expected level of ∼700 ppmv for business‐as‐usual scenarios. Thus, based on the SOFeX results and currently available technology, large–scale oceanic iron fertilization appears not a feasible strategy to sequester anthropogenic CO2.