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Northern Hemisphere snow cover

Northern Hemisphere snow cover

The environmental importance of high-latitude snow cover is well established. As well as its role in albedo feedback it is an indicator of the global climate, though a complex one since a warming climate can have both positive effect through increased precipitation and a negative effect through increased melting. It also has a major impact on terrestrial vegetation through thermal insulation, modification of hydrological fluxes and limiting the availability of photosynthetically active radiation. This in turn provides a link to the global carbon cycle. This is a complex set of interactions, which dictates a need for long-term monitoring of snow cover in conjunction with other climatological variables.

Excluding the great ice sheets of Antarctica and Greenland, snow cover is primarily a phenomneon of the northern hemisphere, and there is considerable interest in monitoring its long-term variations and linking these to climate change. Suitable data can be derived from satellite observations and from surface meteorological stations. The satellite dataset extends from the late 1960s, and although surface measuarements are in principle available from much earlier dates it is only since about the same era that hemisphere-wide data have been provided with a reasonably dense coverage.

The aim of this project is to analyse estimates of northern hemisphere snowcover data from around 1970 to the present day to identify key trends and to relate them to other climatological variables. The challenge is to understand the different characteristics of datasets derived from surface mesaurements and from different types of spaceborne sensor, and to reconcile them into a single self-consistent time-series. A particular focus of interest is northern Russia, from which few reliable surface data have been available until comparatively recently.

Preliminary analyses of spaceborne data show a decreasing trend in maximum snowcover from around 1970 till around 1990, followed by an increasing trend. Surface meteorological station data for northern Russia appear to be inconsistent with these trends.

Snow cover

Trend in length of snow-covered period derived from satellite data, 1990-2004. Red indicates decreasing trend, blue increasing trend, grey no trend. No meaningful trend could be calculated for uncoloured pixels.

Weekly snow extent in the northern hemisphere, 1972-2004. The movie is based on: Armstrong, R.L., and M.J. Brodzik. 2005. Northern Hemisphere EASE-Grid weekly snow cover and sea ice extent version 3. Boulder, CO, USA: National Snow and Ice Data Center. Digital media.