Past, present, and future of global aerosol climatologies derived from satellite observations: A perspective

A number of passive satellite instruments have been used to develop global climatologies of terrestrial tropospheric aerosols by analyzing the properties of sunlight reflected by the atmosphere–surface system. The outcome of these efforts are several climatologies which all purport to represent the same aerosol characteristics such as optical thickness and size. However, the quantitative differences between these climatologies have been found to far exceed the corresponding individual uncertainty claims. The magnitude of these differences is alarming and necessitates a detailed critical assessment and integrated analysis that would go far beyond simple intercomparisons of various satellite products and comparisons of satellite aerosol optical thickness results with ground-based sun-photometer data. This paper outlines the framework for a global long-term satellite climatology of aerosol properties based on a consistent combination of previous, current, and near-future satellite retrievals. We also discuss potential future strategies for deriving a much improved aerosol climatology from Earth-orbiting satellites.