What can cloud observations tell us about climate variability?

Clouds have a large impact on the Earth's radiation budget and hence have the potential to exert strong feedbacks on climate variability and climate change. These feedbacks are not well-understood, so it is essential to investigate observed relationships between cloud properties and other parameters of the climate system. Suitable cloud datasets based on surface observations and satellite observations are described and various advantages and disadvantages of each are discussed. In particular it is noted that significant inhomogeneities likely exist in the datasets which have important implications for studies of climate variability. Recommendations are made for the use of cloud data in future investigations.