Detectability of Change in the Ocean Carbon Sink

The ocean has accumulated 39% of all carbon emitted due to anthropogenic activities. Climate models indicate that for an RCP8.5 scenario, the global ocean should absorb anthropogenic carbon at an increasing rate through the middle of this century, and afterwards at a slowing rate. Given that the ocean carbon sink substantially modulates climate change, it is critical to develop optimal strategies to monitor and understand its evolving behavior. Efforts to do so have led to a variety of conflicting results, particularly in the North Atlantic and Southern Ocean. A key challenge has been the inability to distinguish anthropogenically-forced trends from the internal variability inherent to the climate system. We use an innovative modeling approach that allows for this separation: a Large Ensemble. Our analysis reveals both where the ocean carbon sink can be expected to be steady, increasing or decreasing through 2100, and also where internal variability limits detectability of this change. Increasing uptake should occur at high latitudes, in eastern boundary upwelling zones and the equatorial oceans, but steady uptake can be expected across much of the subtropics. Internal variability increases the timeframe for detection most significantly in the equatorial Pacific, the Labrador and Greenland/Iceland Seas and in the subantarctic zone of the Southern Ocean.