The impact of clouds on optical Earth-space links is assessed by means of theoretical analyses. The spacecraft is assumed geostationary so that a stationary model can be considered for the link availability. Binary and continuous attenuations are analysed separately. With a network of ground stations, both spatial diversity and multiplexing are considered. The impact of the ground-station network size and spatial correlation on the availability and throughput is studied. Using a continuous attenuation model, it is shown that an adaptive data rate essentially mitigates thin clouds (on the order of 10-dB attenuation).