1. Musk Oxen Ringed Seal Snowfall Rate Sea-ice Extent Snow Depth 2090-2099 Arctic Precipitation and Its Climatic and Ecological Impacts by Cecilia Bitz with help from Kevin Rennert, Ian Eisenman, Xiyue Sally Zhang, Naomi Goldanson, and Wei Cheng

3. IPCC AR4 Figure 10.9

4. IPCC AR4 Figure 10.3.9

5. Net Evaporation Atlantic Ocean What drives the Atlantic MOC? But is this right?

6. Gregory et al 2005 Fraction of AMOC change caused by Heat Flux Changes Fraction of AMOC change caused by Freshwater Changes In Greenhouse Warming Scenarios Heat Flux causes Atlantic MOC to Weaken

7. IPCC AR4 Fig 10.5 Atlantic MOC Projections (SRES A1B)

8. Rahmstorf (1996) At equilibrium if MOC has net northward salt transport, dense water must be created thermally Rahmstorf said: If MOC has northward salt transport and it weakens, then Atlantic should freshen and further stabilize ocean – yielding a positive feedback More recent view: Weaker MOC displaces Hadley circulation southward, reducing F1 and destabilizing ocean – yielding a negative feedback

9. Net Evaporation Atlantic Ocean I’m not claiming that the Atlantic is not net evaporative The point is that the AMOC may not transport the freshwater needed to balance evaporation. Instead it is probably accomplished by the gyre circulations I am saying the modern AMOC strength may not be much influenced by local surface haline forcing

10. W MOC = - ∫ dz v (S-S o ) v is the zonally integrated northward current, S is the zonal mean salinity, and S o is the reference salinity 1 S o < 0 via surface: MOC is thermally driven > 0 via surface: MOC is both thermally and haline driven W MOC at ~ 33S Freshwater* Transport by MOC (opposite sign as salt transport) Climate W MOC LGM 0.26 Sv Modern 0.03 Sv 4XCO2 -0.03 Sv CCSM3 runs *Corrected after talk

11. Northern North Atlantic Density Profiles 4XCO2 Modern LGM

12. surface density anomaly from 1000kg/m 3 (shading), sea ice edge (black), and deep mixing (green) Surface Density, Sinking Locations, and Sea Ice Edge ModernLast Glacial Maximum (LGM) model result kg/m 3

13. Diapycnal volume flux, G And diffusion, D D()D() D(+)D(+) G(  +  )/(  +  ) G(  )/  ++  Integrate the density flux over area of outcroppings: ∂  T,S ∂  = convergence into the outcropping Mass flux In MOC  T,S (  ) Mass Balance Nurser et al, 1999 outcrop  T,S (  ) = ∫ dA F T,S (  ) Surface density influx Watermass formation rate is (neglecting diffusion) Watermass Formation Rate

14. surface density (a nomaly from 1000kg/m 3) Atlantic Watermass Formation Rate from 30-65N from observations from Surface Heat Fluxes from Surface Freshwater Fluxes Densest water in the North Atlantic is created locally from Surface Heat Flux Loss, NOT Evaporation Speer and Tziperman 1992

15. Thermal flux component Haline flux component time density g cm -3 Creation of dense water Destruction of less dense water

16. Eisenmen, Bitz, Tziperman, 2009 Represent receding ice sheets using 3 snapshots (before, during, and after YD). Simulate to approx steady-state

17. Reduce Ice Sheet Height and meridional wind increases so more moisture moisture transport Eisenmen, Bitz, Tziperman, 2009

19. Temperature Change for Medium Height Ice Sheet minus Large Ice Sheet Eisenmen, Bitz, Tziperman, 2009

20. Details: Atmospheric water vapor budget [ P  E ] =  Stationary advection and eddy flux convergence both lead to greater surface freshwater flux.

21. Issues Involving Snow

22. Snowfall Rate (mm/d) Sea-ice Extent (10 6 km 2 ) Snow Depth (cm) 2000-2009

26. Snowfall Rate (mm/d) Sea-ice Extent (10 6 km 2 ) Snow Depth (cm) 2000-2009 Snowfall Rate (mm/d) Sea-ice Extent (10 6 km 2 ) Snow Depth (cm) 2090-2099

27. 35 30 25 20 15 10 5 0 CCSM3 April Snow Depth (cm)

28. 1-10cm 10-20cm >20cm Area (10 6 km 2 ) partitioned by April snow depth on sea ice 2040-2049 2090-2099 CCSM3 2000-2009

29. 2090-2099

30. CCSM3 A1B

31. HadGEM1 A1B CanESM2 RCP8.5 CCSM4 RCP8.5 Every model we have been able to find with snow depth data agrees: snow depth drops precipitously in the 21 st century

32. Case Study: Banks Island, Oct. 2003 20,000 DIE FROM BANKS ISLAND RAIN ON SNOW

33. Case Study: Banks Island, Oct. 2003 20,000 DIE FROM BANKS ISLAND RAIN ON SNOW Musk Oxen

34. Mechanism for impact of ROS on Caribou Ice layers within snow pack increase difficulty of foraging. Heat released can lead to lichen spoilage. Under extreme circumstances, can lead to large scale die-off of herd.

35. Permafrost

36. Case Study: Banks Island, Oct. 2003 Banks Island is generally well below freezing at this time of year. Climatological 500 mb height field with Surface Temperature Banks Island Rennert et al 2009

37. Case Study: Banks Island, Oct. 2003 Banks Island is generally well below freezing at this time of year. Climatological fields for October in the NH show zonal flow across North America Hot pink = freezing temperature Climatological 500 mb height field with Surface Temperature Banks Island Rennert et al 2009 20 15 10 5 0 -5 -10 -15 -20

38. Case Study: Banks Island, Oct. 2003 October 3rd, 2003 Surface Temperature Banks Island Rennert et al 2009 20 15 10 5 0 -5 -10 -15 -20

39. Case Study: Banks Island, Oct. 2003 Order of Events 1. 6 inch snowpack 2. Week of southerly flow, intermittent drizzly rain 3. Thick ice layer forms as temperatures plummet. 4. Widespread starvation of thousands of musk oxen October 3rd, 2003 500 mb height field with Surface Temperature Banks Island Rennert et al 2009 20 15 10 5 0 -5 -10 -15 -20

40. PNA Index Sept 15th - Oct 15th, 2003 Time period of rain October 3rd, 2003 500 mb height field with Surface Temperature Banks Island Rennert et al 2009 20 15 10 5 0 -5 -10 -15 -20 Case Study: Banks Island, Oct. 2003

41. Number of Rain on Snow events per year on average from 1980-1999 from ERA 3mm threshold required for snow depth in both panels 3mm in a day rian threshold 10mm in a day rian threshold 100 25 15 8 5 2 1 0.5 0.25 0.1 0

42. Number of Rain on Snow events per year on average from 1980-1999 3mm threshold required for snow depth and 3mm in day rain threshold in both panels CCSM3 ERA 100 25 15 8 5 2 1 0.5 0.25 0.1 0

43. 4 3 2 1 0 -2 -3 -4 Number of Rain on Snow events per year on average from 2080-2099 minus 1980-1999 in CCSM3 3mm threshold required for snow depth and 3mm in day rain threshold in both panels

44. March September Equilibrium Surface Temperature Response to Adding Surface Absorbing Aerosols in Terrestrial Snow and Sea Ice Global Annual Mean = 0.3°C °C Work of Naomi Goldenson

45. September Sea Ice Thickness Change: Mostly an Indirect Response to Surface Absorbing Aerosols in Terrestrial Snow m Work of Naomi Goldenson Global Annual Mean Temperature Change due to Aerosols in Terrestrial Snow Only = 0.2°C

46. Top of Atmosphere Radiative Forcing of Aerosols in Snow and Sea ice Globally = 0.06 W/m 2 W/m 2 Work of Naomi Goldenson

47. Compare Sensitivity of Surface Absorbing Aerosols to CO 2 in CCSM4 Global Mean Radiative Forcing CO 2 is 3.5 W/m 2 Aerosols is 0.06 W/m 2 Global Equilibrium Temperature Change CO 2 is 3.13°C Aerosols is 0.3°C Efficacy of Aerosols = (0.3/0.06) / (3.13/3.5) ~ 6 Work of Naomi Goldenson

48. Compare Sensitivity of Surface Absorbing Aerosols in Sea Ice Only to CO 2 in CCSM4 Global Mean Radiative Forcing CO 2 is 3.5 W/m 2 Sea Ice Aerosols is 0.005 W/m 2 Global Equilibrium Temperature Change CO 2 is 3.13°C Sea Ice Aerosols is 0.1°C Efficacy of Aerosols = (0.1/0.005) / (3.13/3.5) ~ 20 Work of Naomi Goldenson But a bit silly because warming is only 0.1°C?

49. Summary High latitude precipitation is increasing but it is probably not a concern for the modern AMOC In glacial climates, precipitation is a bigger factor in driving AMOC, changes in North American ice sheet height could have driven large changes in precipitation via v (not so much q) Rain falling on snow is increasing, in heavy rainfall events it damages permafrost, but more frequently causes problems for 4 legged creatures Snow depths on sea ice decline substantially and presents a problem for ringed seals, chief reason cited in threatened species petition Aerosols in terrestrial snow are a potent source of Arctic warming

53. 20,000 DIE FROM BANKS ISLAND RAIN ON SNOW Musk Oxen Rennert et al 2009

55. Two Key Result to explain Greater cooling in glacial Longer lasting cooling in glacial Lesson: Glacial response is bad analogy for modern/future And vice versa