Future abrupt reductions in summer Future abrupt reductions in summer Arctic sea ice - CCSM 3.0Arctic sea ice - CCSM 3.0

Marika M Holland Cecilia M Bitz Bruno TremblayMarika M Holland Cecilia M Bitz Bruno Tremblay

Community Climate System Model Community Climate System Model Version 3.0Version 3.0

Coupling: Atmosphere, Land, Ice & OceanCoupling: Atmosphere, Land, Ice & Ocean

http://www.ccsm.ucar.eduhttp://www.ccsm.ucar.edu

/models/ccsm3.0//models/ccsm3.0/

Community Atmosphere Model - Community Atmosphere Model - CAM3CAM3

► T85: 1.4 degree resolutionT85: 1.4 degree resolution► 26 vertical levels26 vertical levels► Anthropogenic GHG scenarios : A1, A2, B1, Anthropogenic GHG scenarios : A1, A2, B1,

B2B2

Future Emission ScenariosFuture Emission Scenarios► A1 : future world very rapid economic growth, global population peaks in mid-A1 : future world very rapid economic growth, global population peaks in mid-

century and declines thereafter, rapid introduction efficient technologies.century and declines thereafter, rapid introduction efficient technologies.► A2 : self-reliance and preservation of local identities, continuously increasing A2 : self-reliance and preservation of local identities, continuously increasing

global population, economic growth and technological changes are slowerglobal population, economic growth and technological changes are slower► B1 : same global population as A1, but with rapid changes toward service & B1 : same global population as A1, but with rapid changes toward service &

information economy, with reductions in material intensity, clean & resource-information economy, with reductions in material intensity, clean & resource-efficient technologies. efficient technologies.

Community Land Model: CLM Community Land Model: CLM 3.03.0

►Subgrid mosaic of plant functional and Subgrid mosaic of plant functional and land cover types taken from satellite land cover types taken from satellite observationobservation

►Same grid as atmosphere except for Same grid as atmosphere except for river routing. Uses 0.5 degree grid.river routing. Uses 0.5 degree grid.

Parallel Ocean ProgramParallel Ocean Program

► Isopycnal transport parameterization Isopycnal transport parameterization with vertical mixing. with vertical mixing.

Isopycnal: surface of constant water Isopycnal: surface of constant water densitydensity

►1 degree resolution with North Pole 1 degree resolution with North Pole displaced into Greenland to avoid displaced into Greenland to avoid converging meridians in Arctic Basinsconverging meridians in Arctic Basins

Community Sea Ice Model: CSIM Community Sea Ice Model: CSIM 5.05.0

► Identical Greenland Pole grid as Parallel Identical Greenland Pole grid as Parallel Ocean ProgramOcean Program

► 5 Ice Thickness & 1 Open Water category5 Ice Thickness & 1 Open Water category► Energy Conserving ThermodynamicsEnergy Conserving Thermodynamics► Elastic-viscous-plastic rheologyElastic-viscous-plastic rheology► Subgrid scale ice thickness distributionSubgrid scale ice thickness distribution

•Thickness EvolutionThickness Evolution•Rafting & ridging distributionRafting & ridging distribution•Ice Strength energeticsIce Strength energetics•Albedo parameterization with implicit melt pondsAlbedo parameterization with implicit melt ponds

Ice Balance - Governing Ice Balance - Governing EquationsEquations

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 RheologyIce Rheology

Ice Behaviour

Elastic Solid

Plastic SolidFluid

IPCC-AR4 ContributionIPCC-AR4 Contribution

► Intergovernmental Panel on Climate Change 4Intergovernmental Panel on Climate Change 4thth assessment reportassessment report

► All model runs include integrations through 1870-All model runs include integrations through 1870-1999 forced with changes in sulfates, solar input, 1999 forced with changes in sulfates, solar input, volcanoes, ozone, GHG’s, halocrabons, black carbon volcanoes, ozone, GHG’s, halocrabons, black carbon from observed record & offline chemical transport from observed record & offline chemical transport models.models.

► Simulations during 21Simulations during 21stst century used Special Report century used Special Report on Emission Scenarios (SRES) A1B scenario. on Emission Scenarios (SRES) A1B scenario.

Observed Arctic Sea Ice Observed Arctic Sea Ice RetreatRetreat

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 Ensemble Member 1 PredictionsPredictions

Abrupt reductions with retreat 3 times faster Abrupt reductions with retreat 3 times faster then observed (1979-2005) trends then observed (1979-2005) trends

20 % loss from 1998 – 200320 % loss from 1998 – 2003Decrease of ~ 4 million kmDecrease of ~ 4 million km2 2 /year in 10 years/year in 10 years

2024 – 2040 rapid retreat with nearly ice 2024 – 2040 rapid retreat with nearly ice free conditions by 2040free conditions by 2040

Ice retreat accelerates with increased Open Ice retreat accelerates with increased Open Water Production Efficiency & ice-albedo Water Production Efficiency & ice-albedo feedbacksfeedbacks

Definition of Abrupt Definition of Abrupt TransitionTransition

►Derivative 5-year running mean smoothed Derivative 5-year running mean smoothed September ice extent > -0.5 M kmSeptember ice extent > -0.5 M km22 /year /year

7 % loss of 2000 ensemble mean7 % loss of 2000 ensemble mean

► Event length determined at transition when Event length determined at transition when smoothed timeseries exceeds a loss smoothed timeseries exceeds a loss

0.15 km0.15 km22/year/year

Ensemble Run 1Ensemble Run 1

Abrupt TransitionsAbrupt Transitions

► Mechanisms & PredictionMechanisms & Prediction

Thermodynamics – Ocean & Atmospheric heat Thermodynamics – Ocean & Atmospheric heat transport during melt season; May through Augusttransport during melt season; May through August

Vs.Vs.Dynamics – Divergence & DeformationDynamics – Divergence & Deformation

Thinning Arctic Ice PackThinning Arctic Ice Pack► Future simulations of thinning Ice linked to Future simulations of thinning Ice linked to

Abrupt Transitions in ice coverageAbrupt Transitions in ice coverageRate & Magnitude of thinning ice comparable to Rate & Magnitude of thinning ice comparable to past trends with little ice extent change. past trends with little ice extent change. Why?Why?

► Trend is NON-LINEARTrend is NON-LINEARMelt Season Open Water Production Efficiency =Melt Season Open Water Production Efficiency =

% open water formation per cm of ice melt% open water formation per cm of ice melt

► A given melt rate has more influence on A given melt rate has more influence on minimum summer ice extent as the ice gets minimum summer ice extent as the ice gets thinner due to accelerated thinner due to accelerated OOpen pen WWater ater FFormationormation

Open Water Formation Open Water Formation EfficiencyEfficiency

Critical Ice Thickness ?Critical Ice Thickness ?

► Link between thickness and Rate of OWF suggestsLink between thickness and Rate of OWF suggests

Critical Point = Total potential Summer MeltCritical Point = Total potential Summer Melt

► 7 ensemble members provide no evidence7 ensemble members provide no evidenceSimulated natural variability & forced change Simulated natural variability & forced change “contaminate” an identifiable critical ice thickness“contaminate” an identifiable critical ice thickness

► Recent changes suggest the Arctic has reached a Recent changes suggest the Arctic has reached a “tipping point” with strong + feedbacks “tipping point” with strong + feedbacks

Arctic Radiation BalanceArctic Radiation Balance

► Increased OWF reduces the Arctic Albedo Increased OWF reduces the Arctic Albedo

Ocean absorbs more SWR. Greater basal Ocean absorbs more SWR. Greater basal ice melt rate and delayed autumn growth.ice melt rate and delayed autumn growth.

► Increased fresh water flux through Increased fresh water flux through Canadian Archipelago & Fram Strait Canadian Archipelago & Fram Strait reduces MOC in North Atlantic.reduces MOC in North Atlantic.

Artic Ocean Heat TransportArtic Ocean Heat Transport

► Strengthened ocean currents & southern warm water Strengthened ocean currents & southern warm water enter Arctic increasing OHT despite weakening MOC enter Arctic increasing OHT despite weakening MOC in North Atlantic south of Denmark Strait. in North Atlantic south of Denmark Strait. WHY?WHY?

Weaker insulation of thinner ice cover causes larger Weaker insulation of thinner ice cover causes larger ice production, brine rejection and ocean ventilation ice production, brine rejection and ocean ventilation

Abrupt increases in OHT modifies summer Ice Abrupt increases in OHT modifies summer Ice growth/melt ratesgrowth/melt rates

+ feedback accelerating the ice retreat. + feedback accelerating the ice retreat.

T / T / Z = -QZ = -Qo o / / KKii

Arctic Sea Ice AnimationArctic 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 OHT & Absorbed SWR – Ice ThicknessThickness

Biases in a Simulated Arctic?Biases in a Simulated Arctic?

►Does the modeled Atlantic heat flux Does the modeled Atlantic heat flux compare well with observed record?compare well with observed record?

►How unique is the abrupt September How unique is the abrupt September ice transition in Ensemble Run 1?ice transition in Ensemble Run 1?

►How robust are the processes involved How robust are the processes involved in the transition?in the transition?

Observed vs. Simulated OHTObserved vs. Simulated OHT

►2020thth century observations show a century observations show a warming of the intermediate (150-warming of the intermediate (150-900m) depth Atlantic layer within the 900m) depth Atlantic layer within the Arctic Ocean. (Gradual superimposed Arctic Ocean. (Gradual superimposed with pulse-like events)with pulse-like events)

►Similar trend produced in simulations Similar trend produced in simulations supporting the Model resultssupporting the Model results

Ensemble Member Model Ensemble Member Model RunsRuns

► from 7 ensemble membersfrom 7 ensemble members

Model runs compare well with observationsModel runs compare well with observations

Abrupt Transitions are a Common FeatureAbrupt Transitions are a Common Feature

4 X faster then that observed between 1979-20054 X faster then that observed between 1979-2005Minimum 2.6 time faster. Minimum 2.6 time faster. ~ -0.4 M km ~ -0.4 M km22/year/year

All abrupt transitions are thermodynamically All abrupt transitions are thermodynamically drivendriven

Additional Archived ModelsAdditional Archived Models

►6 / 15 IPCC-AR4 model archives with 6 / 15 IPCC-AR4 model archives with A1B scenarios have abrupt transitions.A1B scenarios have abrupt transitions.

►(SRES B1) slower anthropogenic GHG (SRES B1) slower anthropogenic GHG rate 3/ 15 have abrupt transitionsrate 3/ 15 have abrupt transitions

►(SRES A2) greater anthropogenic GHG (SRES A2) greater anthropogenic GHG rate 7/ 11 exhibit abrupt retreat with rate 7/ 11 exhibit abrupt retreat with larger rates of changelarger rates of change

The Reality of Abrupt ChangeThe Reality of Abrupt Change

►Simulations warn that they will Simulations warn that they will become common events in the futurebecome common events in the future

►Changes in human GHG emissions Changes in human GHG emissions policies could help reduce the riskpolicies could help reduce the risk

►Earliest event approximated in 2015Earliest event approximated in 2015

~ 2.5 M km~ 2.5 M km2 2 lost in 5 yearslost in 5 years

Consequences - PrecipitationConsequences - Precipitation

► Increase in summer evaporation causing Increase in summer evaporation causing greater cloudiness and sea-smoke.greater cloudiness and sea-smoke.

►Greater summer precipitation over Greater summer precipitation over circumpolar landscircumpolar lands

Increased Mountain GlaciationsIncreased Mountain Glaciations Increased run-off over thawing Canadian tundraIncreased run-off over thawing Canadian tundra

Great turbidity in costal watersGreat turbidity in costal watersSediment loading in Arctic rivers and basinSediment loading in Arctic rivers and basin

Consequences – Atmospheric Consequences – Atmospheric DynamicsDynamics

► Possible northward shift of the Jet StreamPossible northward shift of the Jet Stream

► Change in local pressure intensitiesChange in local pressure intensities Weaker Polar Highs (Weaker Polar Easterlies)Weaker Polar Highs (Weaker Polar Easterlies) Deeper Stronger lowsDeeper Stronger lows

► Frictional coupling of ice ate air/sea interface Frictional coupling of ice ate air/sea interface reduced forcing new patterns of arctic circulationreduced forcing new patterns of arctic circulation

Sea surface roughness will increase costal Sea surface roughness will increase costal erosionerosion

Consequences – FW flux & Consequences – FW flux & MOCMOC

Consequences – Social & Consequences – Social & EconomicEconomic

► Adaptation to climate change by native peoples in Adaptation to climate change by native peoples in Canadian TerritoriesCanadian Territories

Strain on social behavior and subsidence strategiesStrain on social behavior and subsidence strategies

► Improved ice conditions will will increase shipping Improved ice conditions will will increase shipping through the arctic for a longer season.through the arctic for a longer season. Through passages Europe-PacificThrough passages Europe-Pacific Supply Routes into Arctic communitiesSupply Routes into Arctic communities

International Polar Year 2007-International Polar Year 2007-20082008

► International effort to better understand International effort to better understand Polar environments and climatePolar environments and climate

► Canadian Proposal ThemesCanadian Proposal Themes Indigenous & Western Knowledge TraditionsIndigenous & Western Knowledge Traditions Contaminants in Polar Environment & Human Contaminants in Polar Environment & Human

SystemsSystems Arctic Archipelago ThroughflowArctic Archipelago Throughflow Environmental Genomics & Renewable ResourcesEnvironmental Genomics & Renewable Resources Earth Atmosphere Ocean ExchangesEarth Atmosphere Ocean Exchanges Earth Observation (RADSAT 2 March 2007) Earth Observation (RADSAT 2 March 2007)

IPY ProposalIPY Proposal

► Measurements & modeling of delta O18 and Measurements & modeling of delta O18 and Lead-210 vertical profilesLead-210 vertical profiles

(internal temperature and salinity) (internal temperature and salinity)

Study heat & brine fluxes through sea ice to Study heat & brine fluxes through sea ice to better understand ice growth & melt better understand ice growth & melt dynamicsdynamics

► The search for the Franklin expedition: a new The search for the Franklin expedition: a new perspective based on Inuit oral tradition perspective based on Inuit oral tradition

Figure 4Figure 4