Terrestrial Cryosphere Summary
Section Coordinator: Marco Tedesco
National Science Foundation, Division of Polar Programs,
Arctic Sciences Section, Arlington, VA, USA
Department of Earth and Atmospheric Science,
The City College of New York, New York, NY, USA
November 13, 2013
The Terrestrial Cryosphere section includes reports on Snow, Glaciers and Ice Caps outside Greenland, the Greenland Ice Sheet, Lake Ice and Permafrost. Each essay draws on field and satellite observations made through the end of summer 2013, with the exception of Glaciers and Ice Caps outside Greenland, for which 2013 data were not available at the time of writing. The Glaciers and Ice Caps essay is further affected by the absence of data from Russia. These limitations in the timeliness and availability of data illustrate the continued challenges that scientists and society face in the effort to observe and understand what is happening throughout the rapidly changing Arctic.
The observing year for the Terrestrial Cryosphere section began in autumn 2012, when lake ice freeze-up occurred earlier than the average for 2004-2012 in all regions of the Arctic. Then, in spring 2013, lake ice break-up occurred earlier than the average throughout the Arctic. The early lake ice break-up was consistent with observations of snow cover extent, which reached a new record low for May in Eurasia, and was below the spring (April, May, June) average for the entire Northern Hemisphere. In 2013, as in 2012, the long-term rate of reduction of June snow cover extent (-19.9% per decade relative to the 1981-2010 average) was greater than the long-term reduction of September sea ice extent (-13.7% per decade relative to the 1981-2010 average).
Once the terrestrial snow cover has melted, warming of the frozen ground begins in earnest as a seasonal active layer with temperatures >0°C develops above the permafrost. In summer 2013, the strongest trends for increasing active layer thickness since the mid-1990s occurred in Interior Alaska, the Russian European North, East Siberia and the Russian Far East. On the North Slope of Alaska, where the long-term active layer thickness change signal is weaker, there were new record high permafrost temperatures at 20 m below the surface in the two northernmost boreholes. New record high permafrost temperatures also occurred at sites in the Brooks Range, Alaska, and in the High Canadian Arctic.
Active layer thickness has also increased since the late 1990s at some Greenland locations. However, from an Arctic terrestrial cryosphere, and indeed global environmental, perspective it is the Greenland Ice Sheet that attracts most attention. After the record surface melt extent and duration of summer 2012, melt extent and duration in summer 2013 were below the average for 1981-2010, and the surface albedo (reflectivity) was above the average for 2000-2011. These observations are consistent with summer surface air temperatures that were normal with respect to the period 1981-2010, particularly along the west coast, where the equilibrium line altitude (the highest altitude at which the previous winter's snow survives) was close to the long-term (1990-2010) average and river discharge was below average.