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A Series of Stabilization Runs in the 21st Century What tipping point?

A Series of Stabilization Runs in the 21st Century What tipping point?. Cecilia Bitz, Marika Holland, David Bailey, and Eric deWeaver. Arctic sea ice extent at top of list of tipping points Lenton et al 2008 Al Gore, Jim Hansen, etc. Question posed by R. Lindsay et al., 2005.

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A Series of Stabilization Runs in the 21st Century What tipping point?

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  1. A Series of Stabilization Runs in the 21st Century What tipping point? Cecilia Bitz, Marika Holland, David Bailey, and Eric deWeaver Arctic sea ice extent at top of list of tipping points Lenton et al 2008 Al Gore, Jim Hansen, etc. Question posed by R. Lindsay et al., 2005

  2. Tipping Point Definitions: 1) bifurcation - irreversible transition to a new state 2) small change in forcing causes a large and/or fast change

  3. Sea Ice Outlook Project

  4. September Concentration A1B Scenario with CCSM3 September Ice Extent in one ensemble member 106 km2 Holland, Bitz, and Tremblay, 2006

  5. red = observations colors = 7 SRES A1B runs w/ CCSM3 black = ensemble mean

  6. CCSM3 Single Year Decline at Least as Big as Observed in 2007 Holland et al. 2008

  7. CCSM3 2001-2050 A1B Scenario - 7 Runs Histogram of 1 yr September Sea Ice Change Even with TREND skew is positive, though probably not significant 4 X in 350 years the drop is as big as observed in 2006-2007 In any decade Observed 2006-2007

  8. Histogram of 400 yr CCSM3 1990s Control Histogram of 1 yr September Sea Ice Change No significant skew so positive and negative 1 year changes are equally likely

  9. Histogram of 320 yr CCSM3 Pre-Industrial Control Histogram of 1 yr September Sea Ice Change Variance is ~2/3 of modern (Because thickness is ~50% greater)

  10. observed Autocorrelation of 400 yr CCSM3 1990s Control September ice cover

  11. A1B Runs - 5 yr smoothing

  12. Now with Commitment Runs 2000 Commitment 2020 Commitment 2030 Commitment A1B Scenario

  13. % Reduction in Area Global Warming - deg C (annual mean area!) Gregory et al., 2002 using HadCM3

  14. Gregory-like plots using CCSM3 A1B Scenario* *Ensemble Average

  15. 2000 Commitment* 2020 Commitment 2030 Commitment A1B Scenario* *Ensemble Average (with envelope)

  16. Observations 1979-2007 A1B Scenario * *Ensemble Average

  17. Pre-Industrial

  18. Pre-Industrial

  19. Summary Sea ice anomalies like 2007 occur about 1% of the time in 21st century CCSM3 runs. Larger anomalies are increasing probable as ice thins Anomalies are not negatively skewed and there is little memory in extent from one September to the next. Bifurcation - irreversible transition to a new state No Evidence! Small change in forcing causes a large and/or fast change Yes!

  20. Pre-Industrial

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