THE SPECIAL CASE FOR UNDERSTANDING CHANGES IN THE ARCTIC

The retreat of Arctic sea ice in summer is fundamentally altering the naval forces’ mission by allowing increasing access to the harsh and highly variable Arctic environment. As stated earlier in this report, the Arctic Ocean is in many ways the most poorly observed of the world’s oceans: there are deficiencies in bathymetric charts, sparse knowledge of sea-ice thickness, infrequent measurements of ocean salinity and temperature, and so on. Current efforts to establish the first comprehensive, sustained in situ observing system in the Arctic are reviewed in this section, as is the state of climate modeling and seasonal forecasts of sea ice and Arctic climate that could prove valuable for planning Arctic operations.

The decline of the yearly minimum sea-ice cover in September is more than 10 percent per decade during the satellite era (since 1979; see Figure 2.3 in the operations section), and the decline appears to be accelerating. According to submarine sonar estimates of draft, the thickness of ice decreased by more than a meter from 1980 to 2000.22 The Canadian archipelago has never allowed ice-free passage in the historical record until two summers in this decade—a prediction that was made at the 2001 symposium on “Naval Operations in an Ice-Free Arctic.”23 Observations and models indicate the Arctic ice cover is losing its multiyear ice and transitioning to a situation more like the Antarctic, which is mostly first-year ice covered with very little sea ice at the end of the melt season.24,25

Natural variability in the sea-ice extent is large in summer, so a given year can be far above or below (by at least 15 percent) the long-term trend. Explanations after the fact for the record minimum in 2007 are many-faceted,26 which is evidence that a complete understanding of the mechanisms of sea-ice variability remains elusive. Predicting such fluctuations would be valuable, and a nascent effort known as the Sea Ice Outlook Project summarizes the community effort to produce Arctic-wide and regional forecasts 2 to 4 months in advance (http://www.arcus.org/search/seaiceoutlook/).

Climate Change Science Program and the Subcommittee on Global Change Research, U.S. Environmental Protection Agency, Washington, D.C., p. ix.

22

D.A. Rothrock, D.B. Percival, and M. Wensnahan. 2008. “The Decline in Arctic Sea-Ice Thickness: Separating the Spatial, Annual and Interannual Variability in a Quarter Century of Submarine Data,” Journal of Geophysical Research, Vol. 113, C05003.

23

See Office of Naval Research, 2001, Naval Operations in an Ice-Free Arctic Symposium: Final Report, Arlington, Va., April.

24

Josefino C. Comiso. 2002. “Warming Trends in the Arctic from Clear Sky Satellite Observations,” Journal of Climate, Vol. 16, pp. 3498-3510.

25

J.A. Maslanik, C. Fowler, J. Stroeve, S. Drobot, J. Zwally, D. Yi, W. Emery. 2007. “A Younger, Thinner Arctic Ice Cover: Increased Potential for Rapid, Extensive Sea-Ice Loss,” Geophysical Research Letters, Vol. 34, L24501.

26

Eric T. DeWeaver. 2008. “Arctic Sea Ice Decline: Introduction,” Arctic Sea Ice Decline: Observations, Projections, Mechanisms and Implications, E.T. DeWeaver, C.M. Bitz, and B. Tremblay (eds.), pp. 1-6.



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