Abstract
Abstract. Spatial and temporal variations of summer sea ice albedo over the Arctic are analyzed using an ensemble of historical CMIP5 model simulations. The results are compared to the CLARA-SAL product that is based on long-term satellite observations. The summer sea ice albedo varies substantially among CMIP5 models, and many models show large biases compared to the CLARA-SAL product. Single summer months show an extreme spread of ice albedo among models; July values vary between 0.3 and 0.7 for individual models. The CMIP5 ensemble mean, however, agrees relatively well in the central Arctic but shows too high ice albedo near the ice edges and coasts. In most models, the ice albedo is spatially too uniformly distributed. The summer-to-summer variations seem to be underestimated in many global models, and almost no model is able to reproduce the temporal evolution of ice albedo throughout the summer fully. While the satellite observations indicate the lowest ice albedos during August, the models show minimum values in July and substantially higher values in August. Instead, the June values are often lower in the models than in the satellite observations. This is probably due to too high surface temperatures in June, leading to an early start of the melt season and too cold temperatures in August causing an earlier refreezing in the models. The summer sea ice albedo in the CMIP5 models is strongly governed by surface temperature and snow conditions, particularly during the period of melt onset in early summer and refreezing in late summer. The summer surface net solar radiation of the ice-covered Arctic areas is highly related to the ice albedo in the CMIP5 models. However, the impact of the ice albedo on the sea ice conditions in the CMIP5 models is not clearly visible. This indicates the importance of other Arctic and large-scale processes for the sea ice conditions.
Highlights
Arctic climate has strongly changed in the last decades (ACIA, 2005)
The sea ice extent in the Arctic in the CMIP5 model ensemble shows a very large spread some improvements are observed compared to the CMIP3 ensemble (Stroeve et al, 2012; Massonnet et al, 2012)
The strong impact of the albedo on the surface energy budget should affect sea ice conditions, and Karlsson and Svensson (2013) showed that the annual amplitude of average Arctic sea ice concentration is higher in models with low summer ice albedos than in models with high summer ice albedo. They did not find any significant relation between ice albedo and trends and absolute values of the ice concentration. We extended this analysis to ice thickness in the Arctic, but we did not find any significant relation between September Arctic ice volume and summer sea ice albedo either
Summary
Arctic climate has strongly changed in the last decades (ACIA, 2005). The observed warming in the Arctic regions is about twice the rate of the global mean warming (ACIA, 2005; IPCC, 2007; Richter-Menge and Jeffries, 2011). The recently released surface albedo product from the Satellite Application Facility on Climate Monitoring (CM-SAF) clouds, albedo and radiation data set (CLARA-SAL, Riihelä et al, 2013a; Karlsson et al, 2013) and sea ice concentration from the Ocean and Sea Ice Satellite Application Facility (OSI-SAF) data set (Eastwood et al, 2010) allow such detailed evaluation of CMIP5 models. This is the main focus of the present study. We discuss the main sources for the cross-model variations and possible implications for the Arctic climate
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