ACCORD BETWEEN OCEAN MODELS PREDICTING UPTAKE OF ANTHROPOGENIC CO2

Models of the ocean provide the best estimate of how much anthropogenic CO2 the ocean can and will absorb. Yet their agreement is only within 40% as characterized by the range of 2.0 +/- 0.8 Gt C yr-1 computed by the Intergovernmental Panel on Climate Change (IPCC) in 1990 from four model estimates. Since then, one of the former results has been updated and two new model estimates have become available. In a reassessment, now with six ocean models and concern for individual model uncertainties, this study found a narrower range of 2.0 +/- 0.5 Gt C yr-1 (38% less than the former uncertainty). Less uncertainty for oceanic uptake of anthropogenic CO2, Means greater certainty for two combined terms in the budget for the global carbon cycle. First the uncertainty of the combined atmosphere plus ocean sink is also nearly halved (now at +/-0.5 Gt C yr-1 for 1980-1989). Second, die uncertainty of the imbalance term (or missing sink) is reduced, but only slightly because most of its large uncertainty remains associated with the difficulty in precisely quantifying deforestation and land use change.