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Abstract

The albedo of the Earth’s surface is the principal driver of the surface radiative energy budget. The largest seasonal and interannual surface albedo variations are linked with the losses and gains of the Earth’s snow and ice cover. As the ongoing warming of the Earth’s cryosphere reduces snow and ice, the surface albedo also diminishes, creating a further warming impact on the climate via the Snow/Ice Albedo Feeback (SIAF). Consequently, there is a clear need for sustained monitoring of the Earth’s surface albedo, particularly for the cryosphere.The Satellite Application Facility on Climate Monitoring (CM SAF), a project of EUMETSAT, seeks to answer this need through the provision of long-term climate data records from homogenized satellite observations. Now, the third edition of CLARA (CM SAF cLouds, ALbedo and Radiation) data record has been produced, with global coverage over 1979-2020 based on the observations of all AVHRR-carrying weather satellites from TIROS-N to Metop-C. We present the CLARA-A3 data record’s surface albedo data, with a focus on the cryosphere at large: the albedo of the snow and sea ice cover of both Northern and Southern Hemispheres. We will also discuss the strengths and limitations of the CLARA-A3 data, the challenges in combining 40 years of observations from 17 different satellites into a consistent whole, and the experiences and results from the extensive pre-release validation effort using in-situ reference data. Particular attention is given to the representativeness problem: how to validate satellite observations with (comparatively) point-like in situ measurements.