Declining summer snowfall in the Arctic: causes, impacts and feedbacks James A. Screen • Ian Simmonds Received: 20 January 2011 / Accepted: 19 May 2011 / Published online: 10 June 2011 Ó Springer-Verlag 2011 Abstract Recent changes in the Arctic hydrological cycle are explored using in situ observations and an improved atmospheric reanalysis data set, ERA-Interim. We document a pronounced decline in summer snowfall over the Arctic Ocean and Canadian Archipelago. The snowfall decline is diagnosed as being almost entirely caused by changes in precipitation form (snow turning to rain) with very little influence of decreases in total pre- cipitation. The proportion of precipitation falling as snow has decreased as a result of lower-atmospheric warming. Statistically, over 99% of the summer snowfall decline is linked to Arctic warming over the past two decades. Based on the reanalysis snowfall data over the ice-covered Arctic Ocean, we derive an estimate for the amount of snow- covered ice. It is estimated that the area of snow-covered ice, and the proportion of sea ice covered by snow, have decreased significantly. We perform a series of sensitivity experiments in which inter-annual changes in snow-cov- ered ice are either unaccounted for, or are parameterized. In the parameterized case, the loss of snow-on-ice results in a substantial decrease in the surface albedo over the Arctic Ocean, that is of comparable magnitude to the decrease in albedo due to the decline in sea ice cover. Accordingly, the solar input to the Arctic Ocean is increased, causing additional surface ice melt. We conclude that the decline in summer snowfall has likely contributed to the thinning of sea ice over recent decades. The results presented provide support for the existence of a positive feedback in association with warming-induced reductions in summer snowfall. Keywords Arctic  Precipitation  Snow  Sea ice  Albedo feedback  Climate change 1 Introduction Recent climate change has been especially pronounced in the Arctic region, with surface temperatures rising two to four times faster than the global average (Solomon et al. 2007; Bekryaev et al. 2010; Miller et al. 2010) and an accompanying rapid decline of sea ice (Serreze et al. 2007; Stroeve et al. 2007). Both the Arctic warming and sea ice loss in the past few decades are unprecedented over at least the last few thousand years (Kaufmann et al. 2009; Polyak et al. 2010). A multitude of climate feedbacks have been proposed that amplify the Arctic surface air temperature response to climate forcing (either natural or anthropo- genic). Whilst some remain poorly understood and their existence unconfirmed (Francis et al. 2009), others, for example the ice-albedo feedback, are already believed to be active and contributing significantly to recent Arctic change (Serreze et al. 2009; Screen and Simmonds 2010a). In its simplest form the ice-albedo feedback can be understood as decreases in sea ice cover, that expose open water with a lower albedo than ice and increase the solar energy absorbed by the coupled ocean-ice-atmosphere system. As the system warms, the sea ice cover further declines reinforcing the warming. The decline in sea ice extent over recent decades and its associated positive feedback have been widely documented (e.g., Serreze and Francis 2006; Perovich et al. 2007; Screen and Simmonds 2010a). However, changes in sea ice cover are not the only driver of the ice-albedo feedback. Changes occurring within the ice pack, for example to its snow cover or melt pond fraction, also contribute (Curry et al. 1995). Such J. A. Screen (&)  I. Simmonds School of Earth Sciences, University of Melbourne, Melbourne, VIC 3010, Australia e-mail: screenj@unimelb.com.au 123 Clim Dyn (2012) 38:2243–2256 DOI 10.1007/s00382-011-1105-2