Arctic Sea Ice Report from NOAA for 2012
November 27, 2012
The Arctic Report Card (www.arctic.noaa.gov/reportcard/) considers a wide range of environmental observations throughout the Arctic, and is updated annually. A major finding of the Report Card 2012 is that numerous record-setting melting events occurred, even though, with the exception of a few limited episodes, Arctic-wide it was an unremarkable year, relative to the previous decade, for a primary driver of melting - surface air temperatures. From October 2011 through August 2012, positive (warm) temperature anomalies were relatively small over the central Arctic compared to conditions in recent years (2003-2010). Yet, in spite of these moderate conditions, new records were set for sea ice extent, terrestrial snow extent, melting at the surface of the Greenland ice sheet, and permafrost temperature.
Large changes in multiple indicators are affecting climate and ecosystems, and, combined, these changes provide strong evidence of the momentum that has developed in the Arctic environmental system due to the impacts of a persistent warming trend that began over 30 years ago. A major source of this momentum is the fact that changes in the sea ice cover, snow cover, glaciers and Greenland ice sheet all conspire to reduce the overall surface reflectivity of the region in the summer, when the sun is ever-present. In other words, bright, white surfaces that reflect summer sunlight are being replaced by darker surfaces, e.g., ocean and land, which absorb sunlight. These conditions increase the capacity to store heat within the Arctic system, which enables more melting - a positive feedback. Thus, we arrive at the conclusion that it is very likely that major changes will continue to occur in the Arctic in years to come, particularly in the face of projections that indicate continued global warming.
A second key point in Report Card 2012 is that changes in the Arctic marine environment are affecting the foundation of the food web in both the terrestrial and marine ecosystems. While more difficult to discern, there are also observations that confirm the inevitable impacts these changes have on a wide range of higher-trophic Arctic and migratory species. Motivated by these linkages and the record-setting environmental changes in the Arctic region, a number of new programs are underway to more effectively measure, monitor and document changes in the marine and terrestrial ecosystems.
Highlights for 2012
During 2012, a number of record or near-record events occurred in relation to the Arctic terrestrial snow cover. Snow cover duration was the second shortest on record and new minima were set for snow cover extent in May over Eurasia and in June (when snow still covers most of the Arctic region) over the Northern Hemisphere. The rate of loss of June snow cover extent between 1979 and 2012 (the period of satellite observation) set a new record of -17.6%/decade, relative to the 1979-2000 mean. Also on land, new record high temperatures at 20 m depth were measured at most permafrost observatories on the North Slope of Alaska and in the Brooks Range, Alaska, where measurements began in the late 1970s.
In Greenland, surface melting on the ice sheet set new records, with melting in some locations lasting up to ~2 months longer than the average (1979-2011) and melting being detected by satellite instruments over ~97 % of the surface in July. Albedo (reflectivity) estimated from satellite measurements (2000-2012) and in-situ measured mass losses at high elevations also set new records in Greenland.
Sea ice extent in September 2012 reached the lowest observed in the satellite record (1979-present), with a related continued decline in the extent of thick multi-year ice that forms in the central Arctic Basin. This record was set despite a relatively high maximum sea-ice extent in March 2012, which was due to extensive ice in the Bering Sea. March to September 2012 showed the largest seasonal decline in sea ice between the maximum and minimum extents during the satellite record. August 2012 was a period of exceptionally rapid ice loss, with accelerated decline during an intense storm in early August in the East Siberian and Chukchi seas. Illustrating the close connection between the timing and extent of the summer sea ice retreat and sea-surface ocean temperatures, a strong cold anomaly was evident in August in the Chukchi Sea due to the persistence sea ice in this area even as the main body of the pack ice retreated northward.
Observations of the Arctic marine ecosystem provide further evidence of linkages between sea ice conditions and primary productivity, with impacts on the abundance and composition of phytoplankton communities. For instance, new satellite remote sensing observations show the near ubiquity of ice-edge blooms throughout the Arctic and the importance of seasonal sea ice variability in regulating primary production. These results suggest that previous estimates of annual primary production in waters where these under-ice blooms develop may be about ten times too low. At a higher trophic level, seabird phenology, diet, physiology, foraging behavior and survival rates have changed in response to higher water temperatures, which affect prey species.
Changes in the terrestrial ecosystem are exemplified by vegetation and mammals. The tundra continues to become more green and in some locations above-ground plant biomass has increased by as much as 26% since 1982. The length of the growing season increased throughout much of the Arctic, e.g., by ~30 days in Eurasia, between 2000 and 2010. There is evidence that the lemming population cycle is decaying, i.e., the time between population peaks is increasing, and the amplitude of the cycle is collapsing to relatively low population densities.
One species most directly affected by lemming population dynamics is the Arctic fox, which depends on them as a primary food source. In Europe, the Arctic fox population has declined to near extinction due to failure to recover from over-harvesting at the start of the 20th Century and the recent absence of lemming peaks. In contrast, the Arctic fox is abundant in North America. However, in both regions, the larger Red fox has been expanding northward, leading to increased competition with the Arctic fox for resources.
The preparation of Arctic Report Card 2012 was directed by a U.S. inter-agency editorial team of representatives from NOAA, the Cold Regions Research and Engineering Laboratory and the Office of Naval Research. The 20 essays in Report Card 2012, representing the collective effort of an international team of 141 researchers in 15 countries, are based on published and ongoing scientific research. Independent, peer-review of the scientific content of the Report Card was facilitated by the Arctic Monitoring and Assessment (AMAP) Program of the Arctic Council. The Circumpolar Biodiversity Monitoring Program (CBMP), the cornerstone program of the Conservation of Arctic Flora and Fauna (CAFF) Working Group of the Arctic Council, was instrumental in soliciting essays in the ecosystem sections of the Report Card. The Arctic Report Card is supported by the NOAA Climate Program Office through the Arctic Research Program.