CMIP1 evaluation and intercomparison of coupled climate models

The climates simulated by 15 coupled atmosphere/ocean climate models partic ipating in the first phase of the Coupled Model Intercomparison Project (CM IP1) are intercompared and evaluated. Results for global means, zonal avera ges, and geographical distributions of basic climate variables are assemble d and compared with observations. The current generation of climate models reproduce the major features of the observed distribution of the basic clim ate parameters, but there is, nevertheless, a considerable scatter among mo del results and between simulated and observed values. This is particularly true for oceanic variables. Flux adjusted models generally produce simulat ed climates which are in better accord with observations than do non-flux a djusted models; however, some non-flux adjusted model results are closer to observations than some flux adjusted model results. Other model difference s, such as resolution, do not appear to provide a clear distinction among m odel results in this generation of models. Many of the systematic differenc es (those differences common to most models), evident in previous intercomp arison studies are exhibited also by the CMIP1 group of models although oft en with reduced magnitudes. As is characteristic of intercomparison results , different climate variables are simulated with different levels of succes s by different models and no one model is "best" for all variables. There i s some evidence that the "mean model" result, obtained by averaging over th e ensemble of models, provides an overall best comparison to observations f or climatological mean fields. The model deficiencies identified here do no t suggest immediate remedies and the overall success of the models in simul ating the behaviour of the complex non-linear climate system apparently dep ends on the slow improvement in the balance of approximations that characte rize a coupled climate model. Of course, the results of this and similar st udies provide only an indication, at a particular time, of the current stat e and the moderate but steady evolution and improvement of coupled climate models.