19_ClimateModels

19_ClimateModels - 11/07/2002 General Circulation Models...

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11/07/2002 ESM 203 - Climate change and climate models 1 1 ESM 203: General Circulation Models (Climate System Models) Fall 2007 2 General Circulation Models s ~ 2 dozen in world ---- all major nations figure that they’d better develop their own technology so they don’t have to trust other nations in negotiations about blame and trade-offs. s National Center for Atmospheric Research, Boulder s Geophysical Fluid Dynamics Lab, Princeton s NASA Goddard Institute for Space Studies, NYC s Canadian s Hadley Centre (UK) s Max Planck Inst. (Germany) s Japan s Different methods, so in detail they predict markedly different regional patterns of change (say, 3-6 ° C different in regional predictions of average winter temperature under doubled carbon dioxide). s But all predict global averages of ~2-5 ° C with polar areas warming more than equator (upto ~10 ° C ). 3 Elements of a climate system model (1) s Atmosphere model s Radiation and energy balance (Earth and Sun) s Interactions between different levels in the atmosphere s Surface effects (albedo) s Clouds, water vapor, CO 2 and other gases, aerosols s Computationally intensive s Atmospheric dynamics s Winds, pressure distribution, boundary-layer processes s Hydrologic cycle s Evaporation and precipitation s Precipitation formation (least reliable part of forecasts) 4 Elements of a climate system model (2) s Land surface model s Soil moisture storage and release s Vegetation roles s Snow and ice s Ocean model s Dynamics, deep water formation, boundary processes s Fine resolution and long integrations, so computationally intensive s Ice sheet model s Sea ice model s “Primitive”
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11/07/2002 ESM 203 - Climate change and climate models 2 5 General Circulation Models s GCMs more general than ‘climate models’ because they contain the behavior of the ocean circulation, terrestrial hydrology, and sea ice. s Ice sheet energetics included, but not dynamics --- leading to underestimation of response to warming s Earliest models didn’t allow ocean to circulate. s Yet ocean is largest store of heat on planet, so subtle changes in its turnover of heat and carbon dioxide have a big effect on calculated temperatures of atmosphere. 6 Conceptual Design of a GCM A. Henderson-Sellers and K. McGuffie, A Climate Modelling Primer, Wiley, 1987 7 Strategy of climate model operation s Begin by specifying atmospheric conditions at a large number of grid points on surface and at a number of elevations above it s Specify boundary conditions everywhere on the lower boundary of the atmosphere: land/ocean/ice; temperature; veg. cover; etc. s Specify the forcing mechanisms you are trying to model the consequences of : Milankovitch variations; CO 2 levels; land use; volcanic dust or aerosol inputs, etc. s
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19_ClimateModels - 11/07/2002 General Circulation Models...

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