Future abrupt reductions in summer Arctic sea ice - CCSM 3.0

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• Future abrupt reductions in summer Arctic sea ice
  - CCSM 3.0
• Marika M Holland Cecilia M Bitz Bruno
  Tremblay

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Community Climate System Model Version 3.0

• Coupling Atmosphere, Land, Ice Ocean
• http//www.ccsm.ucar.edu
• /models/ccsm3.0/

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Community Atmosphere Model - CAM3

• T85 1.4 degree resolution
• 26 vertical levels
• Anthropogenic GHG scenarios A1, A2, B1, B2

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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.

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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

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Community Sea Ice Model CSIM 5.0

• 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

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Ice Balance - Governing Equations
Wind Ocean Shear Stress
2D Sea Ice Motion
2D Continuity Eq. Height Concentration
Thermodynamic Source Terms
Conservation Energy - T Atm., Ocean Land
Atmosphere-Ice Heat transfer
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Ice Rheology
Ice Behaviour Elastic Solid Plastic Solid Fluid
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IPCC-AR4 Contribution

• Intergovernmental Panel on Climate Change 4th
  assessment report
• All model runs include integrations through
  1870-1999 forced with changes in sulfates, solar
  input, volcanoes, ozone, GHGs, halocrabons,
  black carbon from observed record offline
  chemical transport models.
• Simulations during 21st century used Special
  Report on Emission Scenarios (SRES) A1B scenario.

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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
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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

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Definition of Abrupt Transition

• Derivative 5-year running mean smoothed September
  ice extent gt -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

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Ensemble Run 1
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Abrupt Transitions

• Mechanisms Prediction
• Thermodynamics Ocean Atmospheric heat
  transport during melt season May through August
• Vs.
• Dynamics Divergence Deformation

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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

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Open Water Formation Efficiency
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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

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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.

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Artic Ocean Heat Transport

• 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
• Abrupt increases in OHT modifies summer Ice
  growth/melt rates
• feedback accelerating the ice retreat.

• ?T / ?Z -Qo / Ki

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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
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OHT Absorbed SWR Ice Thickness
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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?

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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

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Ensemble Member Model Runs

• 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

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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

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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

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Consequences - Precipitation

• Increase in summer evaporation causing greater
  cloudiness and sea-smoke.
• Greater summer precipitation over circumpolar
  lands
• Increased Mountain Glaciations
• Increased run-off over thawing Canadian tundra
• Great turbidity in costal waters
• Sediment loading in Arctic rivers and basin

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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

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Consequences FW flux MOC
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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

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International Polar Year 2007-2008

• International effort to better understand Polar
  environments and climate
• Canadian 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)

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IPY Proposal

• Measurements modeling of delta O18 and Lead-210
  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

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Figure 4