Musk Oxen Ringed Seal Snowfall Rate Sea-ice Extent Snow Depth 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

IPCC AR4 Figure 10.9

IPCC AR4 Figure

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

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

IPCC AR4 Fig 10.5 Atlantic MOC Projections (SRES A1B)

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

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

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 4XCO Sv CCSM3 runs *Corrected after talk

Northern North Atlantic Density Profiles 4XCO2 Modern LGM

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

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

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

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

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

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

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

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

Issues Involving Snow

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

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

CCSM3 April Snow Depth (cm)

1-10cm 10-20cm >20cm Area (10 6 km 2 ) partitioned by April snow depth on sea ice CCSM

CCSM3 A1B

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

Case Study: Banks Island, Oct ,000 DIE FROM BANKS ISLAND RAIN ON SNOW

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

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.

Permafrost

Case Study: Banks Island, Oct 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

Case Study: Banks Island, Oct 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

Case Study: Banks Island, Oct October 3rd, 2003 Surface Temperature Banks Island Rennert et al

Case Study: Banks Island, Oct 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, mb height field with Surface Temperature Banks Island Rennert et al

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

Number of Rain on Snow events per year on average from from ERA 3mm threshold required for snow depth in both panels 3mm in a day rian threshold 10mm in a day rian threshold

Number of Rain on Snow events per year on average from mm threshold required for snow depth and 3mm in day rain threshold in both panels CCSM3 ERA

Number of Rain on Snow events per year on average from minus in CCSM3 3mm threshold required for snow depth and 3mm in day rain threshold in both panels

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

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

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

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

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 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?

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

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

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