1. processes responsible for polar amplification of climate change Peter L. LangenCentre for Ice and Climate Niels Bohr InstituteUniversity of Copenhagen

2. Polar amplification of model-projected climate change Peter L. Langen, COGCI School, Jan 27 20092 Holland and Bitz (2003) 15 model intercomparison:

3. Spatial distribution of warming Peter L. Langen, COGCI School, Jan 27 20093 Holland and Bitz (2003) Models with “high” PA

4. Seasonal distribution of warming Peter L. Langen, COGCI School, Jan 27 20094 Holland and Bitz (2003) … but when is the albedo feedback active?

5. Latitude of maximum warming vs. sea ice extent Peter L. Langen, COGCI School, Jan 27 20095 Holland and Bitz (2003) R = -0.80

6. Degree of PA vs. amount of sea ice Peter L. Langen, COGCI School, Jan 27 20096 Holland and Bitz (2003) R = 0.65 R = -0.66 PA seems weakly related to amount of sea ice in weak-to-medium-strength-PA models

7. Snow on land? Peter L. Langen, COGCI School, Jan 27 20097 Holland and Bitz (2003) R = 0.67 … but snow extent correlates also with sea ice extent and not with change in snow

8. Clear-sky and cloud shielding of SAF Peter L. Langen, COGCI School, Jan 27 20098 Qu and Hall (2006) The surface albedo feedback is given by, where

9. In Fourth Assessment Report simulations Peter L. Langen, COGCI School, Jan 27 20099 Qu and Hall (2006)

10. The surface albedo sensitivity Peter L. Langen, COGCI School, Jan 27 200910 Qu and Hall (2006) Inter-model differences in SAF strength derive from parameterizations of surface processes rather than from clouds!

11. Fixed-albedo experiment Peter L. Langen, COGCI School, Jan 27 200911 Hall (2004)

12. Fixed cloud experiment (I) Peter L. Langen, COGCI School, Jan 27 200912 Vavrus (2004)

13. Fixed cloud experiment (II) Peter L. Langen, COGCI School, Jan 27 200913 Vavrus (2004)

14. Effect of fixing low or high latitude clouds only Peter L. Langen, COGCI School, Jan 27 200914 Vavrus (2004) The warming due to low-latitude cloud feedback contributes to high-latitude warming!

15. Peter L. Langen, COGCI School, Jan 27 200915 Ghost forcing experiments Exp 1 Exp 2 Exp 3 Exp 2 Exp 2 + Exp 3 Exp 1 Forcing Response Alexeev, Langen and Bates (2005)

16. Peter L. Langen, COGCI School, Jan 27 200916 Fixed temperature perturbation (I) Tropical-only SST change gives positive high-latitude tendency: Turbulent Radiative Wm -2 Alexeev, Langen and Bates (2005)

17. Peter L. Langen, COGCI School, Jan 27 200917 Fixed temperature perturbation (II) Temperature change (K) Abs. humidity change (g/kg) Ex-trop Uniform Tropical Ex-trop Uniform Ex-trop Tropical Increased heat transport warms and moistens high- latitude troposphere Vertical Profiles at 80N Alexeev, Langen and Bates (2005)

18. Vertical structure of recent Arctic warming Peter L. Langen, COGCI School, Jan 27 200918 Graversen et al. (2007) 1979-2001

19. Peter L. Langen, COGCI School, Jan 27 200919 Polar amplification as an excitation of a preferred mode of response Two different forcings … and very similar responses Manabe and Wetherald (1980): Early GCM experiments Manabe and Wetherald (1980)

20. Peter L. Langen, COGCI School, Jan 27 200920 Surface budget and mixed-layer model Vector containing all surface temperatures Heat capacity of water column Vector containing surface fluxes. Collection of “external” parameters: CO 2, solar constant, etc. Langen and Alexeev (2007)

21. Peter L. Langen, COGCI School, Jan 27 200921 Linearization Langen and Alexeev (2007)

22. Peter L. Langen, COGCI School, Jan 27 200922 External forcing 0 in new equilibrium “forcing” Climate change Langen and Alexeev (2007)

23. Peter L. Langen, COGCI School, Jan 27 200923 Forcing excites least stable mode Linear estimate Actual run Langen and Alexeev (2005) Forcing expanded in basis of eigenvectors If k’th term dominates Least stable mode

24. Peter L. Langen, COGCI School, Jan 27 200924 Perturbation decay in linear system Time (years) Langen and Alexeev (2007)

25. Peter L. Langen, COGCI School, Jan 27 200925 Two-box energy balance model Langen and Alexeev (2007)

26. Peter L. Langen, COGCI School, Jan 27 200926 EBM (II) Alexeev et al. (2005): Tropical perturbation Global Extra-tropical Langen and Alexeev (2007)

27. Peter L. Langen, COGCI School, Jan 27 200927 Eigenanalysis Fast mode Slow mode Langen and Alexeev (2007)

28. Peter L. Langen, COGCI School, Jan 27 200928 Response to steady forcing Langen and Alexeev (2007)

29. Peter L. Langen, COGCI School, Jan 27 200929 Decay in GCM ensemble High lats Global Low lats High lats Global Low lats SW Total Tot-clear LW Langen and Alexeev (2007)

30. Peter L. Langen, COGCI School, Jan 27 200930 Extraction of cloud fields Cloud radiative forcing: SW Total LW positive is warming Langen and Alexeev (2007)

31. Peter L. Langen, COGCI School, Jan 27 200931 Regimes of heat transport sensitivity Caballero and Langen (2005) Climate change experiments are often found to give nearly unchanged heat transports. These experiments follow approximately iso-lines of transport. So when iso-lines are vertical ( ) there is no polar amplification.