7.7 Declining summer snowfall in the Arctic: Causes, impacts and feedbacks

Thursday, 5 May 2011: 10:45 AM
Rooftop Ballroom (15th Floor) (Omni Parker House )
James Screen, University of Melbourne, Melbourne, Victoria, Australia; and I. Simmonds

We explore recent changes in the Arctic hydrological cycle based on in situ observations and the latest atmospheric reanalysis data set. In particular, we focus on a pronounced decline in summer snowfall over the Arctic Ocean and Canadian Archipelago. We diagnose that this snowfall decline is almost entirely caused by changes in precipitation form (snow turning to rain) with little influence of changes in total precipitation. The proportion of precipitation falling as snow has decreased as a result of lower atmospheric warming. Statistically, over 99% of the snowfall decline is linked to Arctic warming over the past two decades. Based on snowfall data over the ice-covered Arctic Ocean, we derive a proxy index for snow-covered ice. We estimate that area of snow-covered ice, and the proportion of sea ice covered by snow, have decreased significantly. In a series of sensitivity experiments, we examine the impact this loss of snow cover has had on the albedo of sea ice. The loss of snow-on-ice results in a substantial decrease in surface albedo over the Arctic Ocean, and is of comparable magnitude to decrease in albedo due to the decline of sea ice cover. Accordingly, the solar energy 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. We will end with some discussion of temperature-snowfall-ice feedbacks and their implications for the future state of the Arctic.
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