Ice Sheets and Climate

Climate modelling is a field in rapid development, and the fltudy of cryospheric processes has become an important part of it. On smaller time scales, the effect of snow cover and sea ice on the atmospheric circulation is of concern for long-range weather forecasting. Thinking in decades or centuries, the effect of a C02 climatic warming on the present-day ice sheets, and the resulting changes in global sea level, has drawn a lot of attention. In particular, the dynamics of marine ice sheets (ice sheets on a bed that would be below sea level after removal of ice and full isostatic rebound) is a subject of continuous research. This interest stems from the fact that the West Antarctic Ice Sheet is a marine ice sheet which, according to some workers, may be close to a complete collapse. The Pleistocene ice ages, or glacial cycles, are best characterized by total ice volume on earth, indicating that on 4 5 large time scales (10 to 10 yr) ice sheets are a dominant component of the climate system. The enormous amount of paleoclimatic information obtained from deep-sea sediments in the last few decades has led to a complete revival of iriterest in the physical aspects of the Pleistocene climatic evolution.

1. The Global Climate System.- 1.1 The global energy balance.- 1.2 The zonal mean state.- 1.3 Zonal asymmetry.- 1.4 The oceans.- 1.5 The seasonal cycle.- 2. How Ice Sheets Affect Climate.- 2.1 Ice sheets and the global energy budget.- 2.2 The temperature — ice — albedo feedback.- 2.3 Albedo feedback and external forcing.- 2.4 Feedback involving the ocean circulation.- 2.5 Effect of ice sheets on the zonal mean climatic state.- 2.6 Planetary waves in the atmosphere.- 3. Modelling of Ice Flow.- 3.1 Some aspects of continuum mechanics.- 3.2 Conservation laws.- 3.3 Application to ice flow.- 3.4 Perfect plasticity.- 3.5 Modelling vertically-integrated ice flow.- 3.6 Steady-state profiles of an ice sheet.- 3.7 Normal stresses.- 3.8 Ice shelves.- 3.9 Equilibrium profiles of an unconfined ice shelf.- 4. Numerical Ice—Sheet Models.- 4.1 A model driven by shearing stresses only.- 4.2 Boundary conditions.- 4.3 Modelling the ice sheet - ice shelf junction.- 4.4 An ice sheet on a sloping bedrock.- 5. The Heat Budget of Ice Sheets.- 5.1 The thermodynamic equation.- 5.2 Some basic solutions.- 5.3 The total heat budget of an ice sheet.- 5.4 An approximate method to calculate the temperature field.- 6. Interaction of Ice Flow and Heat Budget.- 6.1 Temperature dependence of the flow parameter.- 6.2 The basic mechanism of instability.- 6.3 Numerical experiments with a temperature dependent flow law.- 6.4 The effect of basal water.- 6.5 The effect of temperature—dependent flow on the equilibrium profile of a free—floating ice shelf.- 7. Bedrock Adjustment.- 7.1 Introduction.- 7.2 Deflection of the lithosphere.- 7.3 The flow in the asthenosphere.- 7.4 An example.- 8. Basic Response of Ice Sheets to Environmental Conditions.- 8.1 Ice sheets on a bounded continent.- 8.2 A semi-infinite continent and a sloping snow line.- 8.3 Linear perturbations.- 8.4 The effect of orography.- 9. More about Environmental Conditions.- 9.1 Ablation.- 9.2 Accumulation.- 9.3 The zonal mean energy balance.- 9.4 Albedo feedback as a latitude-dependent problem.- 9.5 Including continental ice sheets.- 10. The Glacial Cycles of the Pleistocene.- 10.1 Observational evidence of ice ages.- 10.2 The astronomical theory.- 10.3 Stability of northern hemisphere ice sheets.- 10.4 Simulation of the ice volume record.- 10.5 Further remarks.- 11. The Ice Sheets of Greenland and Antarctica.- 11.1 Short description.- 11.2 Ice shelves and ice streams.- 11.3 Grounding—line migration.- 11.4 A model of the Antarctic Ice Sheet.- 11.5 Surging of ice sheets.- 12. Ice Sheets in the Future.- 12.1 The signal—to—other effects ratio.- 12.2 The carbon dioxide problem.- 12.3 The next ice age.- Epilogue.- References.