Observed changes in the albedo of the Arctic sea ice zone between 1982-2009

The surface albedo of the Arctic sea ice zone is a crucial component in the energy budget of the Arctic region [1, 2]. The treatment of sea ice albedo has been identified as a main source of variability in the future sea ice mass loss forecasts in coupled climate models [3]. There is a clear need to establish datasets of Arctic sea ice albedo to study the changes based on observational data, and to aid future modeling efforts. Here we present an analysis of observed changes in the mean albedo of the Arctic sea ice zone based on such a dataset [4], consisting of 28 years (1982-2009) of homogenized satellite data. Along with the albedo effect of the well-known loss of late-summer sea ice cover [5, 6], we show that the mean albedo of the remaining late-summer Arctic sea ice zone is decreasing. The change per decade in the mean August sea ice zone albedo is -0.029 ± 0.011. With the exception of May mean sea ice zone albedo, all trends are significant with a 99% confidence interval. Variations in sea ice zone albedo can be explained using sea ice concentration surface air temperature, and elapsed time from onset of melt as drivers. Our goal in this paper is to present and analyze the evolution of the Arctic sea ice black-sky albedo during the last three decades, as observed by the CLARA-A1-SAL (CM SAF cLouds, Albedo and RAdiation AVHRR 1st release Surface ALbedo) dataset. Here, we define ”albedo” as the total solar flux reflectivity of Earth’s surface when all atmospheric absorption and scattering effects have been corrected for (i.e. broadband shortwave directional-hemispherical reflectance). We focus on the melting season of the sea ice (May-August), which offers sufficient solar illumination at high enough solar elevation angles to permit robust surface albedo retrievals. We examine the albedo evolution through the monthly mean products of CLARA-A1-SAL; Figure 1 shows the August monthly mean albedo of the Arctic from four years in the dataset. In August, worsening illumination conditions combined with high cloud fractions often create an area around the North Pole where albedo is not retrievable with the CLARA-A1-SAL algorithm. Our focus is on large-scale changes and trends in the mean surface albedo of