1. Whither Arctic Sea Ice? Walter N. Meier 1, Julienne Stroeve 1, Elizabeth Youngman 2, LuAnn 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, Cambridge, MA Why is Sea Ice Important? Sea ice plays an important role in climate for several reasons: 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. Thus, reducing sea ice can result in a positive feedback, amplifying an initial warming: 2.Sea ice is a physical barrier. 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. Sea ice dampens ocean waves and their impacts, including coastal erosion. Temperature  Ice melt  Albedo  Energy  Heat  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. High Albedo Low Albedo Sea Ice-Albedo Feedback Walrus on ice floe Photo by Mike Webber U.S. Fish & Wildlife Serv. Polar bear on ice floe Polar bears hunt seals on the sea ice Native communities hunt on sea ice Photo by Craig George What is Happening to Sea Ice? Arctic sea ice has been decreasing since the late 1970s, particularly during summer, and the decrease has accelerated in recent years: 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 2007 average extent versus long- term averages (1953-2000 and 1979-2000) September 2002-2007 average extent anomalies 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) 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. Trend = -10.2% per decade 1979 – 2000 Avg. = 7.0x10 6 km 2 2007 = 4.3x10 6 km 2 Arctic September Monthly Sea Ice Extent “Whither Arctic Sea Ice?” is an Earth Exploration Toolbook (EET) chapter, developed by a collaboration of scientists, data providers, educators, and the AccessData 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/ 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. 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/ ImageJ, a freeware image analysis tool, is used to visualize, analyze, animate, and subset data for specific regions of interest. Microsoft Excel, or other spreadsheet software, is used to calculate trends and statistics from the ImageJ output. 1979-2007 October extent montage in ImageJ walt@nsidc.org Whither Arctic Sea Ice? All IPCC AR4 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. Stroeve et al., GRL, 2007 Learning About Arctic Sea Ice Change and Its Impacts