Musk OxenRinged Seal

Snowfall Rate

Sea-ice ExtentSnow 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

IPCC AR4 Figure 10.9

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

Fra

ctio

n o

f AM

OC

ch

ang

e c

aus

ed

by

Fre

shw

ate

r C

ha

nge

s

In Greenhouse Warming Scenarios Heat Flux causes Atlantic MOC to Weaken

IPCC AR4 Fig 10.5 Atlantic MOC Projections (SRES A1B)

Rahmstorf (1996)

At equilibriumif MOC has netnorthward 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

WMOC = - ∫ dz v (S-So)

v is the zonally integrated northward current, S is the zonal mean salinity, and So is the reference salinity

1

So

< 0 via surface: MOC is thermally driven

> 0 via surface: MOC is both thermally and haline driven

WMOC at ~ 33S

Freshwater* Transport by MOC (opposite sign as salt transport)

Climate WMOC

LGM 0.26 SvModern 0.03 Sv4XCO2 -0.03 Sv

CCSM3 runs *Corrected after talk

surface density anomaly from 1000kg/m3 (shading),sea ice edge (black),

and deep mixing (green)

Surface Density, Sinking Locations, and Sea Ice Edge

ModernLast Glacial Maximum (LGM)

model result

kg/m3

Diapycnal volume flux, G

And diffusion, D

D()

D(+)

G(+)/(+)

G()/ +

Integrate the density flux over area of outcroppings:

∂ T,S

∂ = convergence into the outcropping

Mass fluxIn MOC

T,S()

Mass Balance Nurser et al, 1999

outcrop

T,S() = ∫ dA FT,S()

Surface density influx

Watermass formation rate is (neglecting diffusion)

Watermass Formation Rate

surface density (anomaly from 1000kg/m3)

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

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 (106 km2)

Snow Depth (cm)

2000-2009

Snowfall Rate (mm/d)

Sea-ice Extent (106 km2)

Snow Depth (cm)

2000-2009

Snowfall Rate (mm/d)

Sea-ice Extent (106 km2)

Snow Depth (cm)

2090-2099

35 30 25 20 15 10 5 0

CCSM3

April Snow Depth (cm)

1-10cm10-20cm

>20cm

Area (106 km2) partitioned by April snow depth on sea ice

2040-2049

2090-2099CCSM3

2000-2009

2090-2099

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

21st century

Case Study: Banks Island, Oct. 2003

20,000 DIE FROM BANKS ISLAND RAIN ON SNOW

Case Study: Banks Island, Oct. 2003

20,000 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. 2003

• Banks Island is generally well below freezing at this time of year.

Climatological 500 mb height field with Surface Temperature

BanksIsland

Rennert et al 2009

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

BanksIsland

Rennert et al 2009

20

15

10

5

0

-5

-10

-15

-20

Case Study: Banks Island, Oct. 2003

October 3rd, 2003Surface Temperature

BanksIsland

Rennert et al 2009

20

15

10

5

0

-5

-10

-15

-20

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

Rennert et al 2009

20

15

10

5

0

-5

-10

-15

-20

PN

A In

de

x

Sept 15th - Oct 15th, 2003

Time period of rain

October 3rd, 2003500 mb height field with Surface Temperature

BanksIsland

Rennert et al 2009

20

15

10

5

0

-5

-10

-15

-20

Case Study: Banks Island, Oct. 2003

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

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

CCSM3ERA

100

25

15

8

5

2

1

0.5

0.25

0.1

0

4

3

2

1

0

-1

-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

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

mWork 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/m2

W/m2

Work of Naomi Goldenson

Compare Sensitivity of Surface Absorbing Aerosols to CO2 in CCSM4

Global Mean Radiative ForcingCO2 is 3.5 W/m2

Aerosols is 0.06 W/m2

Global Equilibrium Temperature ChangeCO2 is 3.13°CAerosols 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 CO2 in CCSM4

Global Mean Radiative ForcingCO2 is 3.5 W/m2

Sea Ice Aerosols is 0.005 W/m2

Global Equilibrium Temperature ChangeCO2 is 3.13°CSea 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/futureAnd vice versa