In this section, radiation block of climatic model of the Institute of Computational Mathematics (ICM) RAS is presented. General description of the model is given in the CLIMATE section, which also contains description of the considered radiation module. Climate model requires the total fluxes of upward and downward heat and solar radiation in the model atmosphere to be calculated at the time moments chosen by the difference scheme of solving thermohydrodynamics equations. The fluxes thus obtained are further used to determine the tendencies of changes in the temperature of atmospheric layers and are also used in the boundary layer to estimate the changes in the temperature of underlying surface. Owing to extreme complexity of radiation processes in the atmosphere, calculations of the fluxes of interest take excessive time of machine work. However, climate model imposes exacting requirements on effectiveness to different model blocks. To match these requirements, maximum possible parameterization is applied to atmospheric processes, radiation in particular. The given version of the radiation block in the ICM model takes about one third of model’s calculation time.