5_climate_models - Climate Models The climate system is a...

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Climate Models “The climate system is a physico-, chemico, biological system possessing infinite degrees of freedom. Any attempt to model such a complex system is fraught with dangers.”
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Climate Models Andy Ridgewell: All models are wrong (some are less wrong) Models are numerical encapsulations of your preconceptions You learn little when the model fits the data
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Climate Models Used correctly, models provide information about: Past climates The climate system Future climate change
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Climate Models Critical relationship with proxy data Use proxies to determine boundary conditions and to test models outcomes Use climate models to test our interpretations of proxy data Use proxies to test outcomes of models
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Evolution of Climate Models Early work Can the model capture the fundamental characteristics of the atmosphere? Recently Greater demand for prediction What is the impact of doubling CO ?
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Goal of Climate Models Simulate the processes that produce climate Describe the system in terms of basic physical laws Replace processes with physical laws Physical laws represent a reasonable approximation of the system (interactions, feedbacks…)
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Climate Models Parameterization Taking processes that can not be treated explicitly (calculated directly by equations in the model) and relating them to variables that are considered in the model Based on observation or statistical functions = Example- clouds- type and coverage is generally parameterized; albedo; convection Null parameterization- ignore a particular process or group of processes (beware of feedbacks)
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Climate Models Boundary Conditions Physical conditions of the Earth established at the initiation of the model run Solar radiation Land surface temperatures Paleogeography/ land elevations Vegetation Sea surface temperatures CO2 levels Extent of ice sheets… Uncertainty in input = uncertainty in results
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Climate Models Sensitivity tests Alter one boundary condition at a time and analyze the effect Climate reconstructions Change several boundary conditions to simulate past conditions (complicated, lots of unknowns)
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Climate Models Trade off between complexity and computer time Can run simple EBM’s with a BASIC program on a PC Depending on grid space and time step GCM’s can require days (and $$) of super computer time
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Types of Models Energy Balance Models (EBM’s) Focus on the radiation budget
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5_climate_models - Climate Models The climate system is a...

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