Future abrupt reductions in summer Arctic
sea ice - CCSM 3.0
Marika M Holland
Cecilia M Bitz
Bruno Tremblay
Community Climate System Model Version 3.0
Coupling: Atmosphere, Land, Ice & Ocean
http://www.ccsm.ucar.edu
/models/ccsm3.0/
Community Atmosphere Model - CAM3
► T85:
1.4 degree resolution
► 26 vertical levels
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Anthropogenic GHG scenarios : A1, A2, B1, B2
Future Emission Scenarios
A1 : future world very rapid economic growth, global population peaks in mid-century
and declines thereafter, rapid introduction efficient technologies.
► A2 : self-reliance and preservation of local identities, continuously increasing global
population, economic growth and technological changes are slower
► B1 : same global population as A1, but with rapid changes toward service & information
economy, with reductions in material intensity, clean & resource-efficient technologies.
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Community Land Model: CLM 3.0
► Subgrid
mosaic of plant functional and land
cover types taken from satellite observation
► Same
grid as atmosphere except for river
routing. Uses 0.5 degree grid.
Parallel Ocean Program
► Isopycnal
transport parameterization with
vertical mixing.
Isopycnal: surface of constant water density
►1
degree resolution with North Pole
displaced into Greenland to avoid
converging meridians in Arctic Basins
Community Sea Ice Model: CSIM 5.0
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Identical Greenland Pole grid as Parallel Ocean
Program
5 Ice Thickness & 1 Open Water category
Energy Conserving Thermodynamics
Elastic-viscous-plastic rheology
Subgrid scale ice thickness distribution
Thickness Evolution
Rafting & ridging distribution
Ice Strength energetics
Albedo parameterization with implicit melt ponds
Ice Balance - Governing Equations
2D Sea Ice Motion
Wind & Ocean Shear Stress
2D Continuity Eq.
Height & Concentration
Thermodynamic Source Terms
Atmosphere-Ice Heat transfer
Conservation Energy - T Atm., Ocean & Land
Ice Rheology
Ice Behaviour
Elastic Solid
Plastic Solid
Fluid
IPCC-AR4 Contribution
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Intergovernmental Panel on Climate Change 4th
assessment report
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All model runs include integrations through 1870-1999
forced with changes in sulfates, solar input, volcanoes,
ozone, GHG’s, halocrabons, black carbon from observed
record & offline chemical transport models.
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Simulations during 21st century used Special Report on
Emission Scenarios (SRES) A1B scenario.
Observed Arctic Sea Ice Retreat
Right animation: The minimum
concentration of Arctic sea ice in 2005
occurred on September 21, 2005, when the
sea ice extent dropped to 2.05 million sq.
miles, the lowest extent yet recorded in the
satellite record. The yellow line represents
the average location of the ice edge of the
perennial sea ice cover for the years 1979
through 2004. Click on image to view
animation.
Credit: NASA
Ensemble Member 1 Predictions
Abrupt reductions with retreat 3 times faster then
observed (1979-2005) trends
20 % loss from 1998 – 2003
Decrease of ~ 4 million km2 /year in 10 years
2024 – 2040 rapid retreat with nearly ice free
conditions by 2040
Ice retreat accelerates with increased Open Water
Production Efficiency & ice-albedo feedbacks
Definition of Abrupt Transition
► Derivative
5-year running mean smoothed
September ice extent > -0.5 M km2 /year
7 % loss of 2000 ensemble mean
► Event
length determined at transition when
smoothed timeseries exceeds a loss
0.15 km2/year
Ensemble Run 1
Abrupt Transitions
► Mechanisms
& Prediction
Thermodynamics – Ocean & Atmospheric heat
transport during melt season; May through August
Vs.
Dynamics – Divergence & Deformation
Thinning Arctic Ice Pack
► Future
simulations of thinning Ice linked to Abrupt
Transitions in ice coverage
Rate & Magnitude of thinning ice comparable to
past trends with little ice extent change. Why?
► Trend
is NON-LINEAR
Melt Season Open Water Production Efficiency =
% open water formation per cm of ice melt
►A
given melt rate has more influence on minimum
summer ice extent as the ice gets thinner due to
accelerated Open Water Formation
Open Water Formation Efficiency
Critical Ice Thickness ?
► Link
between thickness and Rate of OWF suggests
Critical Point = Total potential Summer Melt
►7
ensemble members provide no evidence
Simulated natural variability & forced change
“contaminate” an identifiable critical ice thickness
► Recent
changes suggest the Arctic has reached a
“tipping point” with strong + feedbacks
Arctic Radiation Balance
► Increased
OWF reduces the Arctic Albedo
Ocean absorbs more SWR. Greater basal ice
melt rate and delayed autumn growth.
► Increased
fresh water flux through Canadian
Archipelago & Fram Strait reduces MOC in
North Atlantic.
Artic Ocean Heat Transport
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Strengthened ocean currents & southern warm water enter
Arctic increasing OHT despite weakening MOC in North
Atlantic south of Denmark Strait. WHY?
Weaker insulation of thinner ice cover causes larger ice
production, brine rejection and ocean ventilation
T / Z = -Qo / Ki
Abrupt increases in OHT modifies summer Ice growth/melt
rates
+ feedback accelerating the ice retreat.
Arctic Sea Ice Animation
Left animation: Arctic sea ice typically reaches its minimum
in September, at the end of the summer melt season, and then
recover over the winter. The 2004-2005 winter-season showed
a smaller recovery of sea ice extent than any previous winter in
the satellite record, and the earliest onset of melt throughout
the Arctic. This visualization shows seasonal fluctuations in
Arctic sea ice derived from the new high resolution AMSR-E
instrument on NASA's Aqua satellite. Click on image to view
animation.
Credit: NASA
Right animation: Sea ice decline is likely to affect future
temperatures in the region. Because of its light appearance, ice
reflects much of the sun's radiation back into space whereas dark
ocean water absorbs more of the sun's energy. As ice melts, more
exposed ocean water changes the Earth's albedo, or fraction of
energy reflected away from the planet. This leads to increased
absorption of energy that further warms the planet in what is
called ice-albedo feedback. Click on image to view animation.
Credit: NASA
OHT & Absorbed SWR – Ice Thickness
Biases in a Simulated Arctic?
► Does
the modeled Atlantic heat flux
compare well with observed record?
► How
unique is the abrupt September ice
transition in Ensemble Run 1?
► How
robust are the processes involved in
the transition?
Observed vs. Simulated OHT
► 20th
century observations show a warming
of the intermediate (150-900m) depth
Atlantic layer within the Arctic Ocean.
(Gradual superimposed with pulse-like
events)
► Similar
trend produced in simulations
supporting the Model results
Ensemble Member Model Runs
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from 7 ensemble members
Model runs compare well with observations
Abrupt Transitions are a Common Feature
4 X faster then that observed between 1979-2005
Minimum 2.6 time faster. ~ -0.4 M km2/year
All abrupt transitions are thermodynamically driven
Additional Archived Models
►6
/ 15 IPCC-AR4 model archives with A1B
scenarios have abrupt transitions.
► (SRES
B1) slower anthropogenic GHG rate
3/ 15 have abrupt transitions
► (SRES
A2) greater anthropogenic GHG rate
7/ 11 exhibit abrupt retreat with larger rates
of change
The Reality of Abrupt Change
► Simulations
warn that they will become
common events in the future
► Changes
in human GHG emissions policies
could help reduce the risk
► Earliest
event approximated in 2015
~ 2.5 M km2 lost in 5 years
Consequences - Precipitation
► Increase
in summer evaporation causing greater
cloudiness and sea-smoke.
► Greater
lands
summer precipitation over circumpolar
 Increased Mountain Glaciations
 Increased run-off over thawing Canadian tundra
Great turbidity in costal waters
Sediment loading in Arctic rivers and basin
Consequences – Atmospheric Dynamics
► Possible
northward shift of the Jet Stream
► Change
in local pressure intensities
 Weaker Polar Highs (Weaker Polar Easterlies)
 Deeper Stronger lows
► Frictional
coupling of ice ate air/sea interface
reduced forcing new patterns of arctic circulation
Sea surface roughness will increase costal erosion
Consequences – FW flux & MOC
Consequences – Social & Economic
► Adaptation
to climate change by native peoples in
Canadian Territories
Strain on social behavior and subsidence strategies
► Improved
ice conditions will will increase shipping
through the arctic for a longer season.
 Through passages Europe-Pacific
 Supply Routes into Arctic communities
International Polar Year 2007-2008
► International
effort to better understand Polar
environments and climate
► Canadian
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Proposal Themes
Indigenous & Western Knowledge Traditions
Contaminants in Polar Environment & Human Systems
Arctic Archipelago Throughflow
Environmental Genomics & Renewable Resources
Earth Atmosphere Ocean Exchanges
Earth Observation (RADSAT 2 March 2007)
IPY Proposal
► Measurements
& modeling of delta O18 and Lead210 vertical profiles
(internal temperature and salinity)
Study heat & brine fluxes through sea ice to better
understand ice growth & melt dynamics
► The
search for the Franklin expedition: a new
perspective based on Inuit oral tradition
Figure 4