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
Dec 27, 2015
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