Incorporation of the C-GOLDSTEIN efficient climate model into the GENIE framework: the "genie_eb_go_gs" configuration of GENIE

Abstract

Abstract. A computationally efficient, intermediate complexity ocean-atmosphere-sea ice model (C-GOLDSTEIN) is incorporated into the Grid ENabled Integrated Earth system modeling (GENIE) framework. This involved decoupling of the three component modules that were re-coupled in a modular way, to allow replacement with alternatives and coupling of further components within the framework. The climate model described here (genie_eb_go_gs) is the most basic version of GENIE in which atmosphere, ocean and sea ice all play an active role. Compared to the original model, latitudinal grid resolution has also been generalized to allow a wider range of surface grids to be used and an altered convection scheme has been added. Some other minor modifications and corrections have been applied. For four default meshes, and using the same default parameters as far as possible, we present the results from spin-up experiments. Evaluation of equilibrium states in terms of composite model-observation errors is demonstrated, with caveats regarding the use of un-tuned key parameters. For each mesh, we also carry out four standard climate experiments, based on international protocols: (i) equilibrium climate response (sensitivity) to doubled atmospheric CO2 concentration; (ii) transient climate response to CO2 concentration, increasing at 1% per annum, until doubling; (iii) response of the Atlantic meridional overturning circulation to freshwater hosing over 100 years; and (iv) hysteresis of the overturning circulation under slowly-varied freshwater forcing. Climate sensitivity and transient climate response lie in the ranges 2.85–3.13°C and 1.67–1.97°C respectively. The Atlantic overturning collapses under 0.1 Sv hosing, and subsequently recovers, for one of the meshes. Hosing at 1.0 Sv, the overturning collapses, and remains collapsed, on all four meshes. The hysteresis experiments reveal a wide range in stability of the initial state, from strongly monostable to strongly bistable. The dependencies of experimental results on choice of mesh are thus highlighted and discussed.