Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 2 3 2006 10.5194/cpd-2-267-2006 http://www.clim-past-discuss.net/2/267/2006/ http://www.clim-past-discuss.net/2/267/2006/cpd-2-267-2006.html http://www.clim-past-discuss.net/2/267/2006/cpd-2-267-2006.pdf 267 283 2006-06-14 Comparing transient, accelerated, and equilibrium simulations of the last 30 000 years with the GENIE-1 model D. J. Lunt M. S. Williamson P. J. Valdes T. M. Lenton Bristol Research Initiative for the Dynamic Global Environment (BRIDGE), School of Geographical Sciences, University of Bristol, U.K. School of Environmental Sciences, University of East Anglia, U.K. Tyndall Centre, U.K. Current affiliation: Quantum Information Group, University of Leeds, United Kingdom We examine several aspects of the ocean-atmosphere system over the last 30 000 years, by carrying out simulations with prescribed ice-sheets, atmospheric CO₂ concentration, and orbital parameters. We use the GENIE-1 model with a geostrophic ocean, dynamic sea-ice, an energy balance atmosphere, and a land-surface scheme with fixed vegetation. A transient simulation, with boundary conditions derived from ice-core records and ice-sheet reconstructions, is compared with equilibrium snapshot simulations, including the Last Glacial Maximum (21 000 years before present; 21 kyrBP), mid-Holocene (6 kyrBP) and pre-industrial. The equilibrium snapshot surface temperatures are all very similar to their corresponding time period in the transient simulation, suggesting that in the last 30 000 years, the ocean-atmosphere system has been close to equilibrium with its boundary conditions. We investigate the method of accelerating the boundary conditions of a transient simulation and find that the Southern Ocean is the region most affected by the acceleration. The Northern Hemisphere, even with a factor of 10 acceleration, is relatively unaffected.