Musk Oxen

1. 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 Musk Oxen Ringed Seal 2090-2099 Snowfall Rate Snow Depth Sea-ice Extent

3. IPCC AR4 Figure 10.9

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

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

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

7. Rahmstorf (1996) At equilibriumif 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

8. I’m not claiming that the Atlantic is not net evaporative Net Evaporation Atlantic Ocean 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

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

10. Surface Density, Sinking Locations, and Sea Ice Edge Last Glacial Maximum (LGM) Modern kg/m3 surface density anomaly from 1000kg/m3 (shading),sea ice edge (black), and deep mixing (green) model result

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

12. Atlantic Watermass Formation Rate from 30-65N from observations Densest water in the North Atlantic is created locally from Surface Heat Flux Loss, NOT Evaporation from Surface Freshwater Fluxes from Surface Heat Fluxes surface density (anomaly from 1000kg/m3) Speer and Tziperman 1992

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

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

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

16. Eisenmen, Bitz, Tziperman, 2009

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

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

19. Issues Involving Snow

20. 2000-2009 Snowfall Rate (mm/d) Snow Depth (cm) Sea-ice Extent (106 km2)

24. 2090-2099 Snowfall Rate (mm/d) Snow Depth (cm) Sea-ice Extent (106 km2) 2000-2009 Snowfall Rate (mm/d) Snow Depth (cm) Sea-ice Extent (106 km2)

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

26. 2000-2009 Area (106 km2) partitioned by April snow depth on sea ice >20cm 2040-2049 10-20cm 1-10cm 2090-2099 CCSM3

27. 2090-2099

28. CCSM3 A1B

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

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

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

32. 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.

33. Permafrost

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

35. Banks Island Case Study: Banks Island, Oct. 2003 Climatological 500 mb height field with Surface Temperature 20 15 10 5 0 -5 -10 -15 -20 • 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 Rennert et al 2009

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

37. October 3rd, 2003 500 mb height field with Surface Temperature Banks Island 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 20 15 10 5 0 -5 -10 -15 -20 Rennert et al 2009

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

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

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

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

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

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

44. Top of Atmosphere Radiative Forcing of Aerosols in Snow and Sea ice Globally = 0.06 W/m2 W/m2 Work of Naomi Goldenson

45. Compare Sensitivity of Surface Absorbing Aerosols to CO2 in CCSM4 • Global Mean Radiative Forcing • CO2 is 3.5 W/m2 • Aerosols is 0.06 W/m2 • Global Equilibrium Temperature Change • CO2 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

46. Compare Sensitivity of Surface Absorbing Aerosols in Sea Ice Only to CO2 in CCSM4 • Global Mean Radiative Forcing • CO2 is 3.5 W/m2 • Sea Ice Aerosols is 0.005 W/m2 • Global Equilibrium Temperature Change • CO2 is 3.13°C • Sea Ice Aerosols is 0.1°C • Efficacy of Aerosols = (0.1/0.005) / (3.13/3.5) ~ 20 But a bit silly because warming is only 0.1°C? Work of Naomi Goldenson

47. 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