Tao Wang

1. The role of snow albedo feedback in Earth’s climate Tao Wang

2. Background Recent temperature change relative to 1961-1990 Source UNEP 2012, Keeping Track of our Changing Environment, original source of data – NASA

3. Background Feedback regulates speed of global warming

4. Background Feedback regulates speed of global warming

5. Background Some large amplifying feedbacks

6. Background Some large amplifying feedbacks Snow albedo feedback

7. Albedo What is Albedo?

8. Albedo Snow has a high albedo

9. Albedo Different snow types

10. Albedo Different snow types

11. Direction and magnitude of snow albedo feedback in extratropical land

12. Snow albedo feedback to climate Snow cover/snow mass Temperature albedo Positive feedback Perturbation absorbed radiation

13. Snow albedo feedback to climate • Northern hemisphere insolation incident upon snowpack peaks • during March-May • Boreal spring is time of maximum snow-albedo feedback strength Snow cover/snow mass Temperature albedo Positive feedback Perturbation absorbed radiation

14. How to quantify snow albedo feedback (W m-2 K-1) Impact of a change in T upon albedo (% K-1) Propogation of albedo change to net shortwave flux • Observation-based albedo (satellite) Temperature (e.g. CRU, reanalysis products) • Model-based GCMs with an interactive albedo and temperature feedback

15. How to quantify snow albedo feedback (W m-2 K-1) Impact of a change in T upon albedo (% K-1) Propogation of albedo change to net shortwave flux • Determined at seasonal cycle • April vs. July • Determined at interannual, decadal and century-scale Linear regression between surface temperature and albedo integrated over spring (extratropical land) or summer (Antarctic)

16. How to quantify snow albedo feedback (W m-2 K-1) Impact of a change in T upon albedo (% K-1) Propogation of albedo change to net shortwave flux • Determined at seasonal cycle • April vs. July • Determined at interannual, decadal and century-scale Linear regression between surface temperature and albedo integrated over spring (extratropical land) or summer (Antarctic)

17. How to quantify snow albedo feedback (W m-2 K-1) Impact of a change in T upon albedo (% K-1) Propogation of albedo change to net shortwave flux • Determined at seasonal cycle • April vs. July • Determined at interannual, decadal and century-scale Linear regression between surface temperature and albedo integrated over spring (extratropical land) or summer (Antarctic)

18. Present SAF strength satellite observation (% K-1) determined at seasonal cycle Fernandes et al. (2009)

19. Impacts of SAF strength on surface warming Xu and Hall (2013)

20. Vegetation controls on SAF strength Tree cover impacts on albedo Loranty et al. (2014)

21. Vegetation controls on SAF strength Tree cover impacts on seasonal SAF Loranty et al. (2014)

22. How about future SAF strength There is a large model spread in SAF Hall and Xu (2007)

23. How about future SAF strength Linking SAF from seasonal cycle to that from climate change Xu and Hall (2013)

24. How about future SAF strength Linking SAF from seasonal cycle to that from climate change Is this really unbiased? Xu and Hall (2013)

25. Factors affecting future SAF strength • Expansion of tree • Disturbance

26. Expansion of tree Predicted changes in Vegetation class (circumpolar region) Observed 2050s scenario Pearson et al. (2013)

27. Expansion of tree Predicted changes in Vegetation class (circumpolar region) Observed 2050s scenario Tree expansion Pearson et al. (2013)

28. Expansion of tree Predicted changes in Vegetation class (circumpolar region) Observed 2050s scenario Tree expansion Pearson et al. (2013)

29. Factors affecting future SAF strength • Expansion of tree • Disturbance

30. Fire occurrence (e.g. West Canada) Jin et al. (2012)

31. Impacts of Fire disturbance Chapin III et al. (2008) Randerson et al. (2005)

32. Impacts of Fire disturbance amplify the albedo contrast Chapin III et al. (2008) Randerson et al. (2005)

33. Impacts of Fire disturbance amplify the albedo contrast Post-fire albedo trajectory !! Chapin III et al. (2008) Randerson et al. (2005)

34. Impacts of Fire disturbance Impacts of burn severity in albedo change Beck et al. (2011)

35. Factors affecting future SAF strength • Expansion of tree • Disturbance • Other factors • (Soot, forest infilling, • change in forest statue)

36. Future directions in earth system models • Masking effects of snow albedo by trees • Parameterisation of post-fire albedo trajectory • Impacts of soot, aerosols and black carbon on albedo

37. Direction and magnitude of snow albedo feedback on ice sheet

38. Snow albedo feedback to climate Snow on ice sheet (Antarctic/greenland) Snow grain size Temperature albedo Positive feedback Perturbation absorbed radiation

39. Snow albedo feedback to climate Snow on ice sheet (Antarctic/greenland) Snow grain size Snow grain size snowfall Temperature albedo albedo Negative feedback Positive feedback Perturbation absorbed radiation absorbed radiation

40. Snow albedo feedback to climate Snow on ice sheet (Antarctic/greenland) Snow grain size Snow grain size snowfall Temperature Which loop is more efficient? albedo albedo Negative feedback Positive feedback Perturbation absorbed radiation absorbed radiation

41. PresentSAF on Antarctic Picard et al. (2013)

42. PresentSAF on Antarctic Positive SAF was significantly compensated by negative SAF Picard et al. (2013)

43. PresentSAF on Greenland Box et al. (2012)

44. How about future SAF for Antarctic Picard et al. (2013)

45. Conclusions • Snow albedo feedback - recent warming and • vegetation controls on its magnitude • Potential Inhibition of Snow albedo feedback by • increased snowfall • Future directions in well representing • Snow-albedo feedback in models

46. Thanks a lot for your attention!

47. How Fire influences albedo • Stand replacing fire increased albedo in Alaskan boreal forests. • Recovery to pre-fire albedo ~ 55 years • Albedo had a larger impact on radiative forcing than did fire emissions (CO2, aerosols, etc.)‏ Winter Summer Randerson et al. (2006)‏