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Arctic Sea Ice – Now and in the Future

Arctic Sea Ice – Now and in the Future. J. Stroeve National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado (CU).

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Arctic Sea Ice – Now and in the Future

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  1. Arctic Sea Ice – Now and in the Future

  2. Arctic Sea Ice – Now and in the Future J. Stroeve National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado (CU) With contributions from S. Drobot, M. Holland, R. Kwok, A. Mahoney, J. Maslanik, W. Meier, M. Serreze, J. Zwally

  3. The Poster Child of Climate Change: Arctic Sea Ice Variability of September Sea Ice Cover (1979-2007) Arctic Sea Ice – Now and in the Future

  4. 2005 Median September Ice Extent 1979-2000 Median September Ice Extent 1953-2000 Median September Ice Extent Ice Loss in 2007 Extended Further Into Central Arctic Arctic Sea Ice – Now and in the Future

  5. Transition Towards Younger Ice • Ice age tracking algorithm from C. Fowler and J. Maslanik show ice 5 years or older now only makes up 10% of the perennial ice pack. Spring 1986 Spring 1990 Spring 2007 Maslanik et al., 2007 Arctic Sea Ice – Now and in the Future

  6. Younger Ice is Thinner Ice Maslanik et al., 2007 • Comparison between ice age and ice thickness from 4 years of spring ICESat GLAS-derived thickness fields from J. Zwally and D. Yi. • Results suggest a decrease in mean thickness of 2.6 m in March 1987 to 2.0 m in March 2007 Arctic Sea Ice – Now and in the Future

  7. Conditions this Spring: Ice Extent/Concentration • Some recovery in winter extent, but still well-below normal Source: nsidc.org/seaice_index Arctic Sea Ice – Now and in the Future

  8. Conditions for Spring 2008: Ice Age Data from C. Fowler and J. Maslanik First-year ice now covers 73% of the Arctic Basin, whereas in 2007 it covered 58%. Arctic Sea Ice – Now and in the Future

  9. Image courtesy of R. Kwok Conditions for Spring 2008: Freeboard Comparison between 2007 and 2008 suggests the seasonal ice cover is 5-10 cm thinner and covers more area in 2008 Arctic Sea Ice – Now and in the Future

  10. 1987 2006 2004 1990 2000 2007 1995 2008 Age as Proxy for Thickness and Volume 1997 Arctic Sea Ice – Now and in the Future

  11. This Spring is Warm April 2008 Air Temperature Anomalies (relative to 1979-2007) Arctic Sea Ice – Now and in the Future

  12. Survival of Winter Formed First Year Ice Arctic Sea Ice – Now and in the Future

  13. Estimated 2008 Minimum Sea Ice Extent • Based on survival rates from previous years (Drobot et al., GRL, submitted) 2007 Record minimum extent: 4.13 mil. sq-km Average estimate: 3.48 mil. sq-km Arctic Sea Ice – Now and in the Future

  14. Does 2007 Represent a Tipping Point? • Tipping Point – what is it? • A threshold at which the sea ice cover rapidly transitions to a new stable (seasonally ice-free) equilibrium state. • Abrupt climate change is often defined in the context of this type of tipping point behavior (e.g. National Research Council, 2002). • Some climate models suggest that a transition towards seasonally ice-free conditions may result from “tipping point” behavior (e.g. Winton, 2006). • Other models suggest abrupt change may happen, but may not constitute a threshold response (e.g. CCSM3). Arctic Sea Ice – Now and in the Future

  15. September Sea Ice Extent Model drop1.8 million sq km, 2024–2025 Observed drop1.6 million sq km, 2006–2007 NCAR CCSM3 model simulation Observations Abrupt Ice Loss • Climate models suggest that once the ice thins sufficiently, it becomes vulnerable to natural variability such that abrupt ice losses may occur (Holland et al., 2006). Arctic Sea Ice – Now and in the Future

  16. The Set up Looks Right • Mean thickness (70-90N) in CCSM3 before abrupt change: 1.71 m • Mean thickness (70-90N) from ICESat in Spring 2007: 1.75 m (data from D. Yi and J. Zwally) Arctic Sea Ice – Now and in the Future

  17. Natural Variability Remains Important! NCAR CCSM3 Mean Ice Thickness vs. Std. Dev. Ice Extent • Natural variability increases with a thinning ice pack until the ice is gone Arctic Sea Ice – Now and in the Future

  18. Thus, Ice May Recover this Summer • If we have a strong cyclonic pattern with attendant cold temperatures as in 1996, we may not set a new record in summer 2008. CCSM3 Run 6 Observations Arctic Sea Ice – Now and in the Future

  19. Run 1: Year 2024 Run 2: Year 2025 Run 3: Year 2030 Run 4: Year 2027 Run 5: Year 2029 Solid line ice extent preceding the event, dashed line, extent after the event From Holland et al. in press Does the Thin Ice Imply a Tipping Point? • If the simulated abrupt transitions are the manifestation of a “tipping point”, then it is likely they would be preceded by a similar critical state Arctic Sea Ice – Now and in the Future

  20. September Ice Extent (106km2) Annual Average Ice Thickness (m) However, Thin Ice Remains Important • Although there is not a “critical” ice thickness (or ice concentration) that precedes rapid ice loss, it remains clear that an abrupt ice loss event is only possible if the ice has thinned adequately. • Other GCMs also show thin ice is needed for large regions of the ice pack to melt completely out. From Holland et al., in press Arctic Sea Ice – Now and in the Future

  21. Concluding Statements • Current models tend to underestimate the observed rate of ice loss (Stroeve et al., 2007) and the large ice loss seen in 2007 typically doesn’t happen until mid-century. • NCAR CCSM3 model simulations show 3 factors that contribute to abrupt transitions: • Thinning sea ice • Pulse-like increases in ocean heat transport to the Arctic • Positive surface albedo feedback. • Ice loss in 2007 is similar in character to abrupt ice loss events simulated by CCSM3 later in this century. Arctic Sea Ice – Now and in the Future

  22. Concluding Statements (cont) • Outstanding question remains whether the abrupt events occur due to a threshold or “tipping point”. • Abrupt ice loss in NCAR CCSM3 seems to represent the interaction of large intrinsic Arctic variability with increasing forced change from rising GHGs. • However, the result of an abruptly changing ice cover would be the same, with considerable impacts on the socio-economics, climate and biological systems in the Arctic. • Summer 2008 is poised for yet another dramatic retreat of the sea ice cover. Arctic Sea Ice – Now and in the Future

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