Whither Arctic Sea Ice Walter N Meier 1

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Whither Arctic Sea Ice? Walter N. Meier 1, Julienne Stroeve 1, Elizabeth Youngman 2,

Whither Arctic Sea Ice? Walter N. Meier 1, Julienne Stroeve 1, Elizabeth Youngman 2, Lu. Ann Dahlman 3, and Tamara S. Ledley 3 1 National Snow and Ice Data Center, Boulder, CO 2 Phoenix Country Day School, Phoenix, AZ 3 TERC, walt@nsidc. org Cambridge, MA Why is Sea Ice Important? What is Happening to Sea Ice? Whither Arctic Sea Ice? Sea ice plays an important role in climate for several reasons: Arctic sea ice has been decreasing since the late 1970 s, particularly during summer, and the decrease has accelerated in recent years: All IPCC AR 4 models show a decline in Arctic sea ice under anthropogenic greenhouse gas forcing, providing high confidence that external forcing is at least partially responsible for the observed decline and it is not simply due to natural variability. However, the climate models are too conservative in their estimates and the observations fall outside the range of the models, even before the extreme 2007 summer melt season. Thus, there are factors not accounted for within the models, such as ice thickness, ocean circulation, and possibly other factors as well. 1. Sea Ice-Albedo Feedback. • Sea ice has a high albedo, meaning that it reflects most of the incoming solar energy. • In contrast, the ocean has a very low albedo and most incoming sunlight is absorbed by the ocean. • Thus, when sea ice is present, much less energy absorbed and the region stays cooler than it be would otherwise. Low Albedo High Albedo • Thus, reducing sea ice can result in a positive feedback, amplifying an initial warming: Temperature Heat Ice melt • September trend is now -10% per decade since 1979. Other months are also declining. • September 2002 -2006 were all 15 -20% below normal. • September 2007 was 40% below normal and 23% lower than the previous record in 2005. • The Arctic could be largely ice-free during at least part of the summer by 2030. • Because of the effects of sea ice discussed on the left, sea ice-free summers will have profound impacts on climate, wildlife, and the peoples of the Arctic September Monthly Sea Ice Extent 1979 – 2000 Avg. = 7. 0 x 106 km 2 Energy Learning About Arctic Sea Ice Change and Its Impacts Sea Ice-Albedo Feedback Trend = -10. 2% per decade • Sea ice blocks the transfer of heat and moisture between the ocean and atmosphere. • The presence of sea ice keeps a region cooler and drier. 2007 = 4. 3 x 106 km 2 Timeseries of September 2007 average extent over the satellite record (since 1979). The decline is statistically significant at the 99% level Comparison of September monthly extent with area of contiguous United States (image by D. Perovich, CRREL) • Sea ice dampens ocean waves and their impacts, including coastal erosion. Polar bear on ice floe Polar bears hunt seals on the sea ice Main page of EET sea ice chapter. Pages contain all information to complete the chapter, including links to data and instructions on obtaining and using the data. Albedo 2. Sea ice is a physical barrier. Walrus on ice floe Photo by Mike Webber U. S. Fish & Wildlife Serv. Stroeve et al. , GRL, 2007 Native communities hunt on sea ice Photo by Craig George 3. Sea ice influences regional and global oceanic and atmospheric circulation patterns. 4. Wildlife (e. g. , polar bears, seals, micro-orgranisms) depend on sea ice to survive. 5. Native communities rely on sea ice for hunting and transportation – it is an intimate part of their traditional culture. 6. Sea ice limits human activities – shipping, military operations, natural resource extraction. September 2007 average extent versus longterm averages (1953 -2000 and 1979 -2000) September 2002 -2007 average extent anomalies Microsoft Excel, or other spreadsheet software, is used to calculate trends and statistics from the Image. J output. “Whither Arctic Sea Ice? ” is an Earth Exploration Toolbook (EET) chapter, developed by a collaboration of scientists, data providers, educators, and the Access. Data team at TERC. EET chapters allow students to explore the Earth system through the use of satellite remote sensing data. http: //serc. carleton. edu/eet/seaice/ NSIDC Sea Ice Index pages provide browse imagery and animations for qualitative evaluation of sea ice changes over the whole region. http: //nsidc. org/data/seaice_index/ Impacts of the decline are already being felt: • Polar bear populations are decreasing in some areas; a recent USGS study predicts a ⅔ reduction in the number of bears by 2050 due to declining sea ice extent. • Native communities traditional knowledge no longer valid, resulting in safety issue and loss of culture; also increased coastal erosion endangers villages. • During summer 2007, the Northwest Passage was traversed in record time by a sailboat. Such routes will become more reliable as sea ice declines. 1979 -2007 October extent montage in Image. J, a freeware image analysis tool, is used to visualize, analyze, animate, and subset data for specific regions of interest.