Earth system models of intermediate complexity: Examining the past to understand the future Andrew...

Earth system models of intermediate complexity: Examining the past to understand the future

Andrew WeaverSchool of Earth & Ocean Sciences

University of Victoria

Future Challenges for Marine Sciences in Canada40th Anniversary Symposium

Bedford Institute of Oceanography

24-25 October 2002

Outline

• Background

• The UVic earth system climate model

• Climate change over the last glacial cycle– The Last Glacial Maximum

– Dansgaard-Oeschger Oscillations & Heinrich events

– Labrador Sea Water formation over the last glacial cycle

– The future of LSW formation?

• Summary and Conclusions

• Future directions and challenges

Background

Funding Agencies:

The use of climate models to examine past climate events is an important avenue of investigation if one is to have confidence in their use for future climate change projections.

Scientific Reasons

There are lots of unsolved puzzles buried within the paleo proxy record that can only be pieced together through the use of climate models including a wide range of climate feedbacks.

Personal Reasons

Its fun! One gets to interact with others in a wide variety of disciplines.

What are earth system models of intermediate complexity?

The EMIC vision of climate models:

The old vision of climate models:

What EMICs exist:

1. Bern 2.5D

10. UVic

2. CLIMBER-23. EcBilt4. EcBilt-CLIO5. IAP RAS6. MPM7. MIT8. MoBidiC9. PUMA

11. IMAGE 2

The UVic Coupled Model

Ocean Component

• 3-Dimensional Ocean General Circulation Model• Based on the GFDL Modular Ocean Model (Pacanowski, 1995; Weaver and Hughes, 1996)• 3.6° (zonal)1.8° (meridional) resolution; 19 vertical levels• Several locally-developed subgrid scale parametrisations

Land elevation and ocean depths in UVic coupled model


Inorganic Carbon Cycle Component

• Dissolved inorganic carbon (DIC) modelled as a passive tracer• Atmospheric pCO2 is free to evolve• Closely follows the protocol set up by the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP) — (Orr et al., 1999)

Air sea flux of carbon dioxide at equilibrium present-day climate. Blue: carbon uptake; Red: carbon outgassing


Sea Ice Component

• Dynamics uses elastic-viscous-plastic rheology (Hunke and Dukowicz, 1997)• Multi-level thermodynamics (Bitz and Lipscomb, 1999; Bitz et al. 2000)• Multi-category thickness distribution (Bitz et al., 2000)

The model uses a rotated coordinate system

UVic model grid showing lines of geographic latitude and longitude in the rotated coordinate system


Continental Ice Sheet Component

• Continental Ice Dynamics Model (Marshall and Clarke, 1997)• Models internal deformation of ice (creep)

(a) no basal sliding(b) no subglacial sediment (bed) deformation (ice stream)

• Vertically-integrated mass balance equation• 3-D momentum equations; ice rheology (Glen 1855, 1958)• Includes a local response to isostatic adjustment (Peltier and Marshall, 1995)• Internal thermodynamics and floating ice shelves usually not included

The UVic Coupled ModelContinental Ice Sheet Component

Comparison between observed and simulated present day northern and southern hemisphere ice sheets

SouthernHemisphere

NorthernHemisphere

MODEL OBSERVED


Land Surface Component• Two versions:

1) Simple bucket Model (Manabe, 1969) modified to allow evaporation to depend on surface roughness

2) Leaky bucket version of Hadley Centre MOSES scheme (Cox et al., 1999)

UVic model present day soil moisture when a simple modified bucket land surface model is used


Terrestrial Dynamic Vegetation Component

• Hadley Centre TRIFFID dynamic global vegetation model (Cox et al. 2000, 2001)• 5 plant functional types (PFT): broadleaf & needle leaf trees, C3 & C4 grass, shrub) in each grid box. • Vegetation dynamics (areal coverage, leaf area index and canopy height of each PFT) driven by net primary productivity, which is a function of climate and CO2 (Foley et al 1996)• Carbon fluxes derived using a coupled photosynthesis-stomatal conductance model (Cox et al. 1998)

Preindustrial (1850) UVic model needle leaf distribution (left) and from present-day IGBP observations (right). The model has not included the consequences of human activity (deforestation into cropland/pastures etc.) whereas the IGBP data does.


Atmospheric Component — A dynamic energy-moisture balance model

• Topography on land with specified lapse rate• Snow models for land and ice• Water vapour feedback (Thompson and Warren, 1982)• CO2 radiative forcing specified • Horizontal heat transport through diffusion• Horizontal moisture transport through advection• Precipitation occurs when relative humidity > 85%

MODELPreindustrial (1850) UVic model precipitation (left) and from the present-day NCEP reanalysis (right). The needle leaf tree distribution associated with the model was shown earlier

NCEP REANALYSIS

The 32 river drainage basins used in the UVic model.


Atmospheric Component — A dynamic energy-moisture balance model

ECMWF Reanalysis (45°N): Near-surface air density vs near surface air temperature


The wind feedback

ECMWF Reanalysis (thick lines);NCEP Reanalysis (thin lines):

Latitudinal variation of parameters a and b in = a + b t

Geostrophic (frictional near equator) wind anomalies for 2 x CO2. Red: ECMWF ReanalysisGreen: NCEP ReanalysisBlack: CCCma AGCM


Evaluation of the wind feedback using CCCma AGCM fields

Zonal mean zonal wind velocity Zonal mean meridional wind velocity


Coupling of the subcomponent models

• Through the exchange of latent, sensible and radiative heat fluxes• Through the exchange of water at the air/sea, air/land or air/sea ice interface• Through brine rejection/ice melt and heat exchange at the sea/sea ice interface

includes a parametrisation for local convection due to brine rejection under multi-category sea ice

• Through a wind feedback

The UVic Coupled Model — ClimatologySurface Air Temperature

Sea Surface Salinity

Sea Surface Temperature

The UVic Coupled Model — Climatology

AtlanticMeridional

Overturning(Sv; 1Sv=106m3s–1)

GlobalMeridional

Overturning(Sv; 1Sv=106m3s–1)

The UVic Coupled ModelSea Ice Climatology

SUMMER WINTER

NorthernHemisphere

SouthernHemisphere

The UVic Coupled ModelAge Tracer Water Mass Analysis

Location of tracer release

27°W

Release in North Pacific Release in Weddell and Ross Seas

Release in North Atlantic

The Climate of the 20th Century

Climate Change over the Last Glacial CycleDansgaard-Oeschger Oscillations and Heinrich Events

Focus of rest of talk

Climate Change over the Last Glacial CycleThe Last Glacial Maximum

UVic Model

CLIMBER-2

CCCma CGCM2

What NADW overturning rate are LGM proxy reconstructions consistent with?

Schmittner, Meissner, Eby, Weaver, 2002: Paleoceanography, in press

Correlation and basin average error for several realisations of NADW formation in UVic model

De Vernal et al. (2000)Seidov et al. (1996)

Present day overturning rate: 21 Sv

LGM rate: 11 Sv

LGM_ADV_1A rate: 14 Sv

Seidov et al. (1996)

De Vernal et al. (2000)

LGM PD_FWF rate: 25 Sv

LGM_ADV_1 rate: 4 Sv

WHY?

SST reconstruction: Warmer than CLIMAP; All model results colder; Strongest overturning SSS reconstruction Fresher than Duplessy/Seidov All model results saltier; Weakest overturning

Meissner, Schmittner, Weaver, Adkins, 2002: Paleoceanography, in press

Experimental set up for Analysis

The Hysteresis of the North AtlanticOverturning

• Use radiocarbon (C14) as a passive tracer with a half life of 5730 years

Difference between extreme states (weak overturning minus strong overturning) of the top to bottom age difference. The locations of ocean sediment cores and deep–sea coral are also shown

Where would one expect to see the largest impact on glacial top-to-bottom age differences due to changes in NADW formation?

What NADW overturning rate are LGM proxy reconstructions consistent with?

Meissner, Schmittner, Weaver, Adkins, 2002: Paleoceanography, in press

Interpolation between equilibria

Proxy record+ error bars

Intersection:model/proxy

NADW: 12.7–18.3 SV

Climate Change over the Last Glacial CycleDansgaard-Oeschger Oscillations and Heinrich Events

Schematic diagram taken from: Alley, 1998: Nature, 392, 335 - 337

Stability of the thermohaline circulation using fully interactive ice sheetSchmittner, Yoshimori, Weaver, 2002: Science, 295, 1489–1493

Investigate Hysteresis behaviour:Apply linearly varying freshwater perturbation

Interstadial state

Samplemetastable

stadial state

2 Stable equilibria

Present Day: Red Glacial: Black

2 Stable equilibria + metastable regime

with < 10 Sv

•Without interactive ice sheet this equilibrium is stable

• With interactive ice sheet this equilibrium is metastable and drifts towards the off state with no NADW formation.

• Extracting freshwater from stadial regime can cause rapid transition to interstadial mode.

• Glacial THC more sensitive than modern THC to freshwater perturbations.

•If interstadial forcing is turned off, LSW formation shuts down and system moves to state with ~10Sv overturning

Dansgaard-Oeschger Oscillations

A. Glacial state ice sheet height and calving rate

B. Calving rate and mass balancedifference immediately after transition from cold stadial to warm interstadial

Growth of ice sheet

Melt of ice sheet

Increasedcalving

Dansgaard–Oeschger Oscillations

Response of NADWformation

Force the transition from a stadial to an interstadial state

Strong sustained evaporation

Weak sustained evaporation Surface mass balance (dashed) and calving rate (solid)

Difference between mass balance and calving rates (solid);Anomalies in Atlantic surface freshwater balance (dashed)

Positive values indicate positive feedback between THCand ice sheet mass balance

Dansgaard–Oeschger Oscillations

A salt oscillator:

Increased THC :

Increased Ice sheet growth

Increased calving (after lag of several hundred years)

Increased freshwater discharge into North Atlantic

Reduced THC

Essentially the EXACT OPPOSITE of the mechanism of: Brocker et al., 1990: Paleoceanography, 5, 469–477.

The global response to changes in NADW formation rate

Surface Temperature Anomaly 500m Temperature Anomaly

QuickTime™ and aGIF decompressor

are needed to see this picture.

QuickTime™ and aGIF decompressor

are needed to see this picture.

Heinrich EventsWhy an abrupt warming after a Heinrich event?

Assess the effects of shutting off ice berg calving followinga Heinrich event at t=0 Sea surface temperatures in Irminger Sea:

Model vs composite of proxy data

Surface air temperatures at GRIP:Model vs composite of proxy data

Sea surface salinities in Irminger Sea:Model vs composite of proxy data

Labrador Sea Water formation over the last glacial cycle

Cottet-Puinel, Weaver, Hillaire-Marcel, de Vernal, Clark, 2002: Quaternary Science Reviews, submitted

• Active deep water formation in the Labrador Sea started around 7 kyr BP

Hillaire-Marcel, de Vernal, Bilodeau, Weaver, 2001: Nature, 410, 1073–1077

• Micropalaeontological data and stable isotope measurements from planktonic and benthic foraminifera in deep Labrador Sea sediment cores

• No analogue during last glacial maximum

Wood, Keen, Mitchell, Gregory, 1999: Nature, 399, 572–575

• Coupled modelling study using Hadley Centre model

• Shutdown of LSW formation as a consequence of global warming

Is there a link between these? Can we understand why?

Labrador Sea Water formation over the last glacial cycleCottet-Puinel, Weaver, Hillaire-Marcel, de Vernal, Clark, 2002: Quaternary Science Reviews, submitted

Preindustrial 125 kyr BP LGM


125 Kyr BP Preindustrial


Last Glacial Maximum

February August


6 & 12 kyr BP equilibria looked like preindustrial equilibrium

A long 21,000 year integration

NADW at ~6 kyr BP

The future of Labrador Sea Water formation?Cottet-Puinel, Weaver, Hillaire-Marcel, de Vernal, Clark, 2002: Quaternary Science Reviews, submitted

What about the future?

The future of Labrador Sea Water formation?

The transient response at year 2100

Warm start at 2100 Cold start 1%/year at 2100 Cold start 2%/year at 2100

The future of Labrador Sea Water formation?

Warm start at 2700 Cold start 1%/year at 2700 Cold start 2%/year at 2700

The quasi-equilibrium response at year 2700

Summary and Conclusions

The UVic ESCM represents a versatile tool too:

1) develop intuition / test parametrisation of physical processes

2) develop and test subcomponent models

3) investigate intricacies of interacting climate feedbacks

4) explore puzzles embedded within the paleo proxy record

Summary and ConclusionsIn particular we have been able to:

1) explore internal consistency of various proxy reconstructions

2) determine that an overturning 40% weaker than today is the best fit at the LGM

3) suggest that different C14 top-to-bottom age difference measurements may be inconsistent and suffer from uncertainty in knowledge of paleo atmospheric C14/C12 history

4) determine quantitatively that the glacial THC was more unstable than the modern THC

5) quantitatively capture a salt oscillator mechanism opposite to that of Broecker et al. (1990) as an explanation of Dansgaard-Oeschger events

6) offer a plausible trigger for the abrupt warming following a Heinrich event (cessation or significant reduction of iceberg calving)

7) determine that the Hillaire-Marcel et al. (2001) hypothesis concerning the absence of LSW formation during the last glacial cycle and its mid-Holocene commencement is consistent with inferences from the UVic ESCM

8) LSW formation may temporarily cease as a consequence of global warming

Future Directions and Challenges

The Fourth IPCC Scientific Assessment (~5 years)

The UVic ESCM will include:

Interactive terrestrial and ocean carbon cycle models Anthropogenic emissions will be specified instead of atmospheric concentration levels

Several dynamic vegetation models (IBIS, LPJ, TRIFFIFD)

Statistical-dynamical atmospheric model

The Fifth IPCC Scientific Assessment (~10 years)

The UVic ESCM will include:

Socioeconomic model Policy options, technology paths, etc will be specified instead of anthropogenic emissions

Future Directions and Challenges

One overarching conclusion throughout all of our research:

The Labrador Sea represents an extremely sensitive region to climate change over the last glacial cycle.

It is an ideal location to concentrate observational efforts aimed at monitoring the oceanic response to anthropogenic climate change.

A 21st century challenge to BIO, through sustained and increased funding from the federal government, is to ensure that this happens.

Earth system models of intermediate complexity: Examining the past to understand the future Andrew...

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