= Climate model
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A <climate model> is a mathematical description of the mechanisms and <statistics> of a <planet>'s <climate change> and variability. A useful hierarchy starts with <conservation of energy> in a <zero-dimensional planetary energy balance>, adds vertical <radiative transfer> and <convection> in a <radiative-convective climate column>, and can resolve three-dimensional <fluid mechanics> and <ocean circulation>. Each level answers different questions. A column can explain why changing an absorber changes surface <temperature>; it cannot locate tomorrow's storm.
Three questions should be kept distinct: what sets an average <temperature>, how fast does it respond to <radiative forcing>, and how large are its unforced fluctuations? <Climate sensitivity> concerns the first, <heat capacity> controls response times, and the <Hasselmann stochastic climate model> illustrates the third. An observational test must compare a predicted observable with an instrument's actual readout, as in the <satellite test of greenhouse spectral change>.
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