ARCTIC SEA ICE
PAST, PRESENT AND
FUTURE
Asgeir Sorteberg, Marianne Skolem Andersen
and Nils Gunnar Kvamstø
Asgeir.Sorteberg@gfi.uib.no; Nils.Kvamsto@gfi.uib.no
SUMMER SEA ICE EXTENT
1979-2008
IPCC TREND: 15%
OBS TREND: 30%
QUESTIONS
• PREDICTIONS – WILL THIS CONTINUE?
• UNDERSTANDING OF THE PROCESSES
• ENVIRONMENTAL AND SOCIO-ECONOMIC IMPACT
ENERGY RESOURCES
25% of remaining oil/gass reserves
estimated to be in the Arctic
Estimated reserves
Rest of
N. Afrika
Caspian Sea the world
Middle East
Arctic
7
1: Barents Sea
2: Southern Kara Sea
and West Siberia
3: Northern Kara Sea
4: Laptev Sea
5: East Siberian Sea
6: Chuchi Sea
7: Alaska North
Slope
8: East Greenland
6
8
5
1
3
4
2
USGS estimates
TRANSPORT
2008
CULTURAL
ECOSYSTEMS
OBSERVATIONS OF SEA ICE
ARCTIC SEA - ICE
Arctic sea ice covers an area
the size of USA
Its separating the relatively
warm ocean from a cold
atmosphere
Maximum sea ice extent
is in March minimum in
September.
NERSC, 2009
ARCTIC SEA ICE EXTENT
Various regional time series back to 1900
Good quality satellite measurements of the total
extent since 1979
OBSERVED CHANGE IN SUMMER
SEA ICE EXTENT
CHANGE IN SEPTEMBER ICE EXTENT
RELATIVE TO 1979-2000 MEAN (Stroeve et al 2009)
Slope = -11.1 (+/- 3.3)% per decade
Area of lost sea ice equal to 7 times
the area of Norway
ARCTIC SEAICE THICKNESS
Submarine data
(upward looking sonar)
• 1958/77 and 1993/97:
Thinning of 42%
Rothrock et al. (1999)
(based on 9 cruises)
•1976 and 1996,
Thinning of 43%
Wadhams and Davis (2001):
(based on 2 cruises)
•1980 to 2000
Thinning 37% (1.25m)
Rothrock et al. (2008)
(based on 34 cruises)
ARCTIC SEAICE THICKNESS
Remote sensing (radar altimetry)
• 1993-2001 wintertime
No significant thinning
Large year to year variability
Laxon et al (2003)
(ERS data up to 81.58N)
• 2003-2008
No significant trend, but
2008 drop
Giles et al. (2008)
(Envisat data, up to 81.58N)
ARCTIC SEAICE THICKNESS
Remote sensing (electromagnetic
induction (EM) from helicopter)
• 2001, 2004, 2007
2007 1m below 2001 and 2004
Haas (2008)
(close to North Pole)
Haas (2008)
ARCTIC SEAICE THICKNESS
1900
1950
Regional extent
(Nordic Seas, Russia)
Satellite extent
Submarine
thickness
Satellite
Thickness (to 81N)
EM
Thickness (north Pole region)
1975
1990 2000 2010
Reduction
Reduction
Summer 30%, annual 8%
Reduction
1 m (40%)
No trend
Reduction
1m
OBSERVATIONS OF
FORCING TERMS
OCEANIC ENERGY BUDGET
Li +Si
Fsfc  Rsfc  QH  QE
OE 
 Li  So  Si     Fo    Fi  Fsfc
t
t
so
L – Latent heat; S – sensible heat
Forcing terms:
• Ice export
• Ocean heat transport and heat content
• Surface flux
Let’s see if there has been changes in some
of these terms
RADIATION TERMS
Reconstructions of the
solar irradiance
2
Last 200 years: S d  0.25 to 2 W/m
Last 50 years: S d  0.2
W/m 2
THE SOLAR MAGNETIC
ACTIVITY CYCLE
INSTRUMENTAL MEASUREMENTS EXIST SINCE 1979
(composite of several instruments)
Qsolar  0 W/m2
RADIATIVE FORCING
Radiative forcing is defined as the change in net
irradiance at the tropopause. Net irradiance is the
difference between the incoming radiation energy and
the outgoing radiation energy in a given climate state
AFTER allowing for stratospheric temperatures to
readjust to radiative equilibrium, but with surface and
tropospheric temperatures and state held fixed at the
unperturbed values. [W/m2]
Qsolar
S d
1  abs stratos   0.05 to 0.2 W/m2

4
RADIATIVE FORCING FROM
ATMOSPHERIC GREENHOUSE GASSES
RADIATIVE FORCING LAST
250 YEARS
GREENHOUSE GASES:
2.63
W/m2
TROPOSPHERIC OZONE:
0.35
W/m2
SOLAR RADIATION:
0.12
W/m2
STRATOSPHERIC OZONE:
-0.05 W/m2
VEGETATION CHANGES:
-0.20 W/m2
PARTICLES FROM POLLUTION:
-0.50 W/m2
PARTICLES EFFECT ON CLOUDS:
-0.70 W/m2
SUM:
IPCC, 2007
IPCC., 2007
1.65 W/m2
HOW DOES ATMOSPHERIC ENERGY
TRANSPORT AFFECT SEA-ICE?
HEAT TRANSPORT ACROSS 60ºN
Smedsrud and Sorteberg, 2008
Model study (Andersen and Sorteberg, 2009)
indicates that the increased atm. energy flux
reduced the sea ice thickness with 20% from
1970-1990
1DICE
• 1D model of the Arctic
AOI (Barents s. not incl)
• Atmosphere is a grey
body in LW and
transparent in SW
• Optical thickness as
vertical coordinate
• 41 classes of sea ice
characterized by Hice,
Hsnow, Tice, area
• Ocean: 350 m column
with mixing at the top
(Björk and Söderkvist, 2002)
FORCING / PRESCRIPTIONS
• Lateral atmospheric and
oceanic energy transport
• Solar rad at TOA
• All precip as snow
• Wind
• Ice export
• River run off
• Input: Monthly values
• Time step: 1 day
(Björk and Söderkvist, 2002)
Sensitivity increase
A more realistic vertical
distribution of the
atmospheric energy transport
results in a higher sea ice
sensitivity to transport
anomalies!
Accuracy of atmospheric
energy transport is important!
Andersen and Sorteberg (2009)
13 member ensemble repeated annual cycle in D.
dD one month at the time
• Larger (non-linear) senstivity for
positive summer perturbations
• Air temperature is close to melting
point in summer
→ extra energy may melt ice
• Larger fraction of open waters and
thin sea ice gives a sea ice cover
that is more sensitive to anomalies
in atmospheric energy transport
• → ice-albedo feed-back
• Ice-albedo feedback gets stronger
and faster with a depth dependent
sea-ice albedo
Andersen and Sorteberg (2009)
Simulated annual sea ice thickness development
Atmospheric energy transport
Ice export
Andersen and Sorteberg (2009)
INCREASED NET OCEANIC ENERGY
TRANSPORT INTO THE ARCTIC?
80TW
40TW
130TW
5TW
40TW
Skagseth, 2008
INCREASED NET OCEANIC ENERGY
TRANSPORT INTO THE ARCTIC?
Possibly more oceanic heat transport
last few years
89N, 166E
Warm water into Arctic does not
necessarily means more melting.
Depends on turbulent mixing
Observations indicates that turbulent
mixing is low outside shelf areas
(Sirevåg, 2008)
Model study (Smedsrud and Sorteberg, 2008) indicates that
an increase in oceanic heatflow of 40TW (5W/m2) over
10 years reduces the ice thickness with 10-15%
INCREASED NET EXPORT OF ICE
OUT OF ARCTIC?
INCREASED NET EXPORT OF ICE
OUT OF ARCTIC?
Smedsrud and Sorteberg, 2008
Kwok, 2008
Satellite data shows no clear trend
in sea ice export, but maybe large
export in 2007/08
Model study (Smedsrud and
Sorteberg, 2008) indicates that
an increase in ice export of 35%
(same as 2007/08 level) over 10
years will reduce ice thickness
with 15-20%, but have large impact
on year-to-year variability
RADIATIVE AND
DYNAMICAL FORCINGS
1900
1950
Atmospheric
heat transport
1990 2000 2010
Increased
Anthropogenic
forcing
Solar
1975
No trend
Increased
Increased
Oceanic heat
transport
?
Ice Export
?
Reduction
No trend Possibly
high
No trend
Possibly
high
CHANGE IN RADIATIVE FORCINGS
SOLAR
POSITIVE FORCING LAST 200 YEARS, NO TREND LAST 50
0.05-0.2 W/m2
ANTROPOGENIC
POSITIVE FORCING LAST 200 YEARS, STRONG TREND LAST 50
1.5 W/m2 LAST 200, 1 W/m2 LAST 50
DYNAMICALLY INDUCED CHANGES
ATMOSPHERIC HEAT TRANSPORT
POSSIBLE POSITIVE TREND LAST 50 YEARS (NEGATIVE LAST 20)
4-6 W/m2 LAST 50, -2.5 W/m2 LAST 25
(NB. values not directly comparable to radiative forcing estimates!)
OCEANIC HEAT TRANSPORT
NO GOOD ESTIMATES OVER LAST 50 YEARS,SOME HIGH VALUES
LAST YEARS
ICE EXPORT
NO GOOD ESTIMATES OVER LAST 50 YEARS,SOME HIGH VALUES
LAST YEARS
RATE OF THE SEA ICE LOSS
THE ENERGY FORCINGS PRECONDITION AND INITIATE THE
CHANGES BUT MAGNITUDE AND TIME SCALE OF THE
FOLLOWING CHANGES ARE MOSTLY RELATED TO THE FEEDBACKS
MAIN SHORT-TERM FEEDBACKS
Water vapor feedback
Lapse rate feedback
Cloud feedback
Surface albedo feedback
Geochemical feedbacks
Dynamical feedbacks
?
2007(?)
THE ALBEDO FEEDBACK
CHANGE IN
RADIATIVE FORCING
CHANGE IN
TEMPERATURE
CHANGE IN
ALBEDO
CHANGE IN
MELTING
IS THIS THE
TIPPING POINT?
1979-2008
IPCC TREND: 15%
OBS TREND: 30%
Is the ice-albedo effect
triggering an accelerated
climate change with global
implications?
FRAMEWORK
1. A change in GHG results in an imbalance/forcing Q
2. The temperature responds ∆Ts to restore balance
Q  TS  TS 
Q

i
i
LTOA
Space
Atmosphere
Surface
S0
1   p 
4
CO2
+ΔCO2  TA4
Climate Feedbacks
Ts ,eq  
Q
Planck  Lapse  water  cloud  albedo
-3.2
-0.84
1.80
0.68
0.26
Planck
Change in
atmospheric
temperature
profile
Water
Vapor
Clouds
Albedo
(snow, ice)
With albedo feedback
40% from snow
35% Arctic sea ice
25% from Antarctic ice
Ts,eq  2.8 C

Without albedo feedback Ts,eq  2.4 C

Without arctic ice albedo feedback Ts,eq  2.65 C
Values from
Soden and Held., 2006
SUMMARY
PRESENT SITUATION
• SUMMER ICE EXTENT REDUCED TWICE AS FAST AS
PROJECTED BY IPCC LAST 30 YEARS
• ICE THICKNESS LOSS IN PROBABLY LARGE, BUT
UNCERTAIN
• LONG TERM ICE LOSS PROBABLY DUE TO INCREASED
LONGWAVE RADIATIVE FORCING AND INCREASED
AND DIFFERENTLY DISTRIBUTED ATMOSPHERIC
ENERGY TRANSPORT
• NON LINEARITIES IN ALBEDO FEEDBACK MAY BE
IMPORTANT FOR EXTREME CHANGES IN EXTENT
LAST FEW YEARS
• INCREASED ICE EXPORT MAY BE IMPORTANT
• TOO EARLY TO CONCLUDE THAT IPCC ESTIMATES ARE
TOTALLY OFF, NEXT 5-10 YEARS WILL GIVE GOOD
INDICATIONS
SUMMARY
FUTURE
LONG-TERM:
CONTINUED LOSS DUE TO LONGWAVE RADIATIVE
FORCING
NEXT DECADE:
OPTION I:
PARTIAL RECOVERY IF ICE EXPORT AND
OCEANIC/ATM HEAT TRANSPORT STAYS
NORMAL
OPTION II:
CONTINUED STRONG REDUCTION DUE TO
NON LINEAR ALBEDO FEEDBACK OR IF ICE
EXPORT AND OCEANIC/ATM HEAT TRANSPORT
STAYS STRONGER THAN NORMAL
SUMMARY
GLOBAL IMPLICATIONS
ARCTIC SEA ICE IS IMPORTANT FOR ARCTIC ECOSYSTEM
AND CULTURE , PROBABLY NOT VERY IMPORTANT FOR
THE GLOBE
That’s all folks!…