FY 2002

Simulations of historical and future anthropogenic CO₂ uptake from 12 global ocean models

Orr, J.C., P. Monfray, O. Aumont, A. Yool, I. Totterdell, K. Plattner, F. Joos, E. Maier-Reimer, M.-F. Weirig, R. Schlitzer, K. Caldeira, M. Wickett, R. Matear, M. Follows, Y. Gao, H. Drange, A. Ishida, Y. Yamanaka, S. Doney, K. Lindsay, J.L. Sarmiento, R.D. Slater, R.M. Key, N. Gruber, C. Sabine, and R. Najjar

In Sixth International Carbon Dioxide Conference, Sendai, Japan, 1–5 October 2001, 151–1054 (2001)

To better evaluate ocean model uncertainties and to set the stage for improving their predictability, we have compared simulations of anthropogenic CO in 12 climatologically forced, coarse-resolution ocean models. Models made standard simulations and underwent centralized analysis as part of the second phase of the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP), an IGBP/GAIM-JGOFS initiative. Models simulated a range of uptake, 2.0 ± 0.4 Pg C/yr, for the 1980's average. Models diverged most in the region south of 30°S, where zonally integrated uptake was largest. The OCMIP models also made two different future scenarios: in the first (IPCC scenario S650), atmospheric CO was stabilized at 650 ppm, and in the second (IPCC scenario IS92a), atmospheric CO continued to increase. In both cases, the range of simulated uptake was ±20% about the mean in year 2100. However, when the S650 scenario was continued until 2300, models only agreed to within ±35%. This divergence with time occurred as the relative proportion of anthropogenic CO uptake increased south of 30°S and as this tracer encroached further into the deep ocean, where differences among models are most dramatic. Evaluation of these models with natural C reveals large differences in a deep-ocean circulation. Models with the lowest future CO uptake had deep waters that were much too old; models with the largest future uptake had deep waters that were much too young. Based on observed C the modern uptake of anthropogenic CO by the real ocean probably lies within the ±20% range simulated by the twelve OCMIP-2 models.