The influence of clouds on the radiation field and on climate is investigated over the North Sea by analyzing NOAA AVHRR data. The derived information was applied to calculate the cloud-climate efficiency at the top of atmosphere and at the surface. The cloud-climate efficiencies in the shortwave spectrum show a cooling effect of the earth/atmosphere system for all clouds and a strong dependence on the solar insolation. For the cloud-climate efficiency in the longwave region always heating of the earth/atmosphere system was observed. Because of the solar zenith angle effect thick high clouds with the same optical properties may lead to different effects in the earth/atmosphere system. A first approach of a comparison of the increasing cloud forcing (heating of the earth-atmosphere system) and an analysis of the relative topography 300/850 hPa shows that the increase of the cloud forcing is well correlated with an increase of the temperature in this layer. The deviation from the long-term mean of the pressure or temperature shows the same behaviour. (orig.).