Event

Abstract: Since preindustrial times, the ocean has absorbed an excess of carbon equivalent to 41% of cumulative fossil fuel emissions, and thus has significantly slowed atmospheric CO2 growth and the resulting climate change. Ocean carbon uptake is expected to grow substantially through 2100. Thus, international climate policy efforts require the carbon cycle science community to regularly diagnose ocean carbon fluxes and to distinguish changes in atmospheric CO2 due to natural variability from changes due to emission cuts. Our analysis of 35 years of surface ocean pCO2 observations illustrates significant large-scale variability on interannual to decadal timescales. If the expected long-term growth in the ocean carbon sink is to be directly detected, the growth signal must emerge from the noise of this variability. We predict emergence timescales using a large ensemble of the NCAR climate model (NCAR-LENS). The forced trend in carbon uptake is largest and emerges most quickly at the high latitudes. In the subtropics, the sink grows slowly and does not emerge until late in the century. Surface ocean pCO2 observations indicate carbon sink growth consistent with the predicted emergence only in the North Pacific; elsewhere, variability continues to dominate.