High Climate Model Dependency of Pliocene Antarctic Ice-Sheet Predictions

The mid-Pliocene warm period provides a natural laboratory to investigate the long-term response of the Earth’s ice-sheets and sea level in a warmer-than-present-day world. Proxy data suggest that during the warm Pliocene, portions of the Antarctic ice-sheets, including West Antarctica could have been lost. Ice-sheet modelling forced by Pliocene climate model outputs is an essential way to improve our understanding of ice-sheets during the Pliocene. However, uncertainty exists regarding the degree to which results are model-dependent. Using climatological forcing from an international climate modelling intercomparison project, we demonstrate the high dependency of Antarctic ice-sheet volume predictions on the climate model-based forcing used. In addition, the collapse of the vulnerable marine basins of Antarctica is dependent on the ice-sheet model used. These results demonstrate that great caution is required in order to avoid making unsound statements about the nature of the Pliocene Antarctic ice-sheet based on model results that do not account for structural uncertainty in both the climate and ice sheet models

Climate studies with a coupled atmosphere-upper-ocean-ice-sheet model

A two-dimensional zonally averaged model has been developed for simulating the seasonal cycle of the climate of the Northern Hemisphere. The atmospheric component of the model is based on the two-level quasi-geostrophic potential vorticity system of equations. At the surface, the model has land-sea resolution and incorporates detailed snow and sea-ice mass budgets. The upper ocean is represented by an integral mixed-layer model that takes into account the meridional advection and turbulent diffusion of heat. Comparisons between the computed present-day climate and climatological data show that the model does reasonably well in simulating the seasonal cycle of the temperature field. In response to a projected CO/sub 2/ trend based on the scenario of Wuebbles et al. (1984), the modelled annual hemispheric mean surface temperature increases by 2 degrees C between 1983 and 2063. In the high latitudes, the response undergoes significant seasonal variations.Anglai

Modelling the transient response of a coupled model to the astronomical forcing over the last glacial to interglacial cycle

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Sensitivity of the European LGM climate to North Atlantic sea-surface temperature

Recent reconstructions of Sea-Surface Temperatures (SSTs) for the Last Glacial Maximum (LGM, 21 kyr BP) based on foraminifera and dinoflagellate proxies suggest that the north Atlantic may have been warmer than estimated by CLIMAP [1981]. To better understand the impact of such a warm north Atlantic on the global LGM climate, we used two different AGCMs to perform sensitivity studies. With the new, warmer SSTs, both models simulate a hydrological cycle and temperatures very different from those obtained with the CLIMAP boundary conditions. The most noticeable differences occur in winter over North America and Siberia whereas southern Europe is only weakly affected at all seasons. Whichever the conditions prescribed over the north Atlantic, both models underestimate the large cooling recorded by continental proxy data over the Mediterranean Basin