Paleoclimate tests of a model of the atmospheric general circulation

Late-Pleistocene and mid-Holocene climate states at three selected ‘time-slices’ within the last ice age cycle have been simulated with the Canadian Climate Centre for modelling and analysis Atmospheric General Circulation Model (CCCma AGCM).; Simulations of the mid-Holocene optimum climate at 6000 years before present (6 ka BP) are performed to test the sensitivity of the model to modifications of the land surface parameterizations. The primary mechanisms responsible for an anomalous model response as compared with other models from the international Paleoclimate Model Intercomparison Project (PMIP) are thereby identified.; An AGCM reconstruction of Last Glacial Maximum (LGM) climate at 21 ka BP was also conducted to test predictions of LGM tropical SSTs and to investigate the mechanisms responsible for the maintenance of the southeasterly lobes of the Laurentide ice sheet. The model simulation of LGM climate is also compared with results from other models in the PMIP set and to the predictions of an intermediate complexity model that has been developed to simulate glacial-interglacial cycles. Model predictions of LGM tropical SSTs are found to be in good agreement with sea surface temperatures (SSTs) inferred from proxy reconstructions of LGM climate.; The onset of continental glaciation that, occurred in the Post Eemian Glacial period (116 ka BP) provides a further means of testing the ability of the CCCma GCM under conditions that differ radically from the modern conditions to which the parameterization schemes in the model are tuned. The analyses described herein demonstrate that entry into glacial conditions at 116 ka BP is successfully predicted when the mixed layer slab ocean component of the CCCma AGCM is constrained to accurately reproduce AMIP2 observed modern SSTs under conditions of modern radiative forcing. A set of sensitivity experiments in which the solar radiation parameterization and the implied oceanic heat transport are modified, reveal a number of novel feedback mechanisms that are key to understanding the initiation of large-scale continental glaciation.