Global water balance and atmospheric water vapour transport at last glacial maximum: climate simulations with the Canadian Climate Centre for Modelling and Analysis atmospheric general circulation model

Abstract

A series of new simulations of the climate state at last glacial maximum has been performed using the Canadian second-generation atmospheric general circulation model and are described herein. The primary goal has been to assess the dynamic changes in the global water balance and water vapour transport that were characteristic of the climate state during this epoch of Earth's history. We pay special attention to comparisons of the atmospheric model simulations of last glacial maximum climate with those produced with a much simpler coupled energy balance-ice-sheet model, which has been designed to simulate the late Pleistocene cycle of glacial-interglacial ice volume variations. Our analyses, using the atmospheric model, demonstrate that the vigour of the hydrological cycle was markedly decreased under last glacial maximum conditions, as would be expected on the simplest thermodynamic grounds. The primary components of the hydrological cycle in the atmospheric model, namely precipitation and evaporation, constitute essential mechanisms that control ice-sheet mass balance. We also investigate changes in the Northern Hemisphere stationary wave patterns, as well as changes in the total and eddy moisture transport by the global circulation at last glacial maximum to illustrate the role played by the dynamics of the atmosphere in the maintenance of the Northern Hemisphere ice sheets. In particular, we find that the enhancement of the stationary wave pattern along with the convergence in atmospheric water vapour transport produces increased cooling and snow accumulation at last glacial maximum over the southeastern lobes of the Laurentide Ice Sheet. This suggests an explanation for the previously unexplained extension of these lobes deep into the New England states.