Quaternary modelling case studies

1) Last Glacial Inception : ~115kyrBP

2) Last Glacial Maximum : ~21kyrBP

3) The mid-Holocene : ~6kyrBP

Focus on 3 important periods in the last 150,000 years.

Mid-Holocene, 6kyrBP

Last Glacial Maximum, 21kyrBP

Glacial Inception, 115kyrBP

Petit et al, Nature, 399, 429-436, 1999.

End of the last interglacial. Initiation of large ice-sheets.

Glacial Inception, 115kyrBP

1) Last Glacial Inception

Northern and Southern hemisphere ice-sheet volume similar to present.

CO2 similar to pre-industrial modern.

Difference: ORBIT!

Higher eccentricity and lower obliquity than present, but perihelion unchanged => cooler NH summers! Vettoretti and Peltier, 2004

Caused by build-up of snow which survives the summer.

Geological evidence points to inception on Queen Elizabeth Islands and Baffin Islands.

Elevation [metres]

See Clark et al, Quaternary Science Reviews, 12, 79-114, 1993.

First modelling studies in 80’s fail to simulate inception.

Mid-90’s, first successful inception experiment.

Ocean temperature changes, accuracy of model’s present-day climate both important. Dong and Valdes, Journal of Climate, 8, 2471-2496, 1995.

Ocean circulation changes also important.

Khodri et al, 2001

Vettoretti and Peltier, 2004

Vegetation changes also important.

Boreal forest/tundra – snow - albedo feedback.

See also de Noblet et al, Geophysical Research Letters, 23, 3191-3194, 1996, Dorman & Sellers 1989

Snowy Forest: low albedo Snowy Tundra: high albedo

Evergreen trees:summer to winter = 10 to 12% - LOW

Evergreen trees:summer to winter = 10 to 12% - LOW

More recent work includes fully dynamic ice sheet models….but relatively simple EMICs…..

Transient simulations

Kubatzki et al, Climate Dynamics (2006) 27: 333–344Kubatzki et al, 2006

See also Loutre, 2002, ‘An Exceptionally Long Interglacial Ahead?’Also papers by Mysak.

Archer and Ganopolski, ‘A movable trigger: Fossil fuel CO2 and the onset of the next glaciation’

Largest mass of land-ice in the last 130,000 years.

Last Glacial Maximum, 21kyrBP

Last Glacial Maximum, 21kyrBP

Last Glacial Maximum, 21kyrBP

Incoming solar radiation distribution very similar to present.

CO2 at approx 185ppmv ( pre-industrial 280ppmv, present approx 380ppmv (and rising!)).

Last Glacial Maximum, 21kyrBP

Observations: global ice-sheet area reconstruction, derived from position of glacial morraines.

Modern [fraction] LGM

Peltier, Science, 265, 195-201, 1994.

Last Glacial Maximum, 21kyrBP

Observations: global topographic reconstruction, derived from observed rebound of lithosphere.

Modern [metres] LGM

Peltier, Science, 265, 195-201, 1994.

Kageyama et al, 2006

ICE-4G ICE-5G

Last Glacial Maximum, 21kyrBP

Observations: global sea-surface temperature: CLIMAP. Derived from bugs, e.g. foraminifera, in ocean sediments.

December

SST, oC

LGM-present

CLIMAP project members, Map and chart ser. MC-36, 1981. For updated version see also Hostetler and Mix, Nature, 399, 673-676, 1999. Also, newer MARGO data.

Kucera et al, 2005

de Vernal et al, 2006

Last Glacial Maximum, 21kyrBP

Observations: global sea-ice extent: CLIMAP, again from ocean sediments.

Modern [fraction] LGM

December

CLIMAP project members, Map and chart ser. MC-36, 1981.

Last Glacial Maximum, 21kyrBP

Observations: terrestrial pollen data.

Kageyama et al, Climate Dynamics, 17, 23-43, 2001

Last Glacial Maximum, 21kyrBP

History of LGM modelling

GCMs with constrained (CLIMAP) SSTs and sea-ice extent, constrained (Peltier ICE4G icesheets), constrained CO2. (PMIP).

GCMs with simple ocean (thermodynamic, not dynamic) and seaice, constrained (Peltier ICE4G icesheets), constrained CO2.

GCMs with fully-dynamic ocean and seaice and vegetation, constrained (Peltier ICE5G icesheets), constrained CO2. (PMIP2).

PMIP2 website: http://www-lsce.cea.fr/pmip2/

PMIP1 website: http://www-lsce.cea.fr/pmip/

Last Glacial Maximum, 21kyrBP

Annual mean, surface temp change, LGM-present day.

July, surface wind strength, LGM.

Hadley centre model results, fixed SSTs, seaice extent.

Jost et al, Climate Dynamics, 2005.

Last Glacial Maximum, 21kyrBP

Hadley-centre model (and others) too warm over Europe! Models are not sensitive enough to the imposed boundary conditions.

Fixed SSTs, seaice.

Hadley-Centre model, 96x72.

Jost et al, Climate Dynamics, 2005.

Last Glacial Maximum, 21kyrBP

PMIP1 models.

All models are too warm relative to present in western Europe at the LGM.

Why?

Inherent model flaws?

Resolution?

Boundary conditions?

Data is wrong?! Kageyama et al, Climate Dynamics, 17, 23-43, 2001

Last Glacial Maximum, 21kyrBP

Fixed SSTs, seaice.

Hadley-Centre REGIONAL model. Very high resolution over Europe. Regional model much better

representation of temperature.

Jost et al, Climate Dynamics, 2005.

Effect of including vegetation changes in the GCM

Ramstein et al, Clim. Past, 3, 331–339, 2007

Effect of including CO2 effects on vegetation…

Clim. Past, 3, 331–339, 2007

Last Glacial Maximum, 21kyrBP

Dynamic ocean and seaice

Was part of the North Atlantic warmer than present?!

Hewitt et al, Climate Dynamics, 20,203-218, 2003

IPCC AR4, Paleoclimate Chapter

Ensemble does not support warm Atlantic

Relative importance of forcings

Bracconnot et al, 2007, Clim Past

Difference between fully coupled (AO), slab, or fixed SSTs…

IPCC AR4, Paleoclimate Chapter

Comparison with data

Downscaling…

Vrac et al, 2007

Period of relative warmth.

Mid-Holocene, 6kyrBP

The mid-Holocene, 6kyrBP

IPCC AR4, Paleoclimate Chapter

Why study 6k?

The mid-Holocene, 6kyrBP

Relatively large northern-hemisphere summer insolation (larger obliquity and eccentricity and change in perihelion)

CO2 at approxpre-industrial - 280ppmv.

Bracconnot et al, 2007, Clim Past

Difference between fully coupled (AO) or fixed SSTs…

The mid-Holocene, 6kyrBP

Tropical forest

Warm-temperate forest

Savanna and dry woodland

Grassland and dry shrubland

Desert

Temperate forest

Boreal forest

Tundra

Dry tundra

Pollen data, cave paintings: A vegetated Sahara!

BIOME 6000:Prentice et al. (2000) Harrison et al. (2001) Bigelow et al. (2003)

http://www.bridge.bris.ac.uk/resources/BIOMES_data/BIOME_v4.2.htm

The mid-Holocene, 6kyrBP

Intensification of the Asian and African Monsoons

See also, Texier et al, Journal of Climate, 13, 164-181, 2000.

However, coupled climate-vegetation models currently unable to generate a green Sahara – not sensitive enough.

JJA precipitation change, mm/day,6kyrBP-preindustrial

Bracconnot et al, 2007, Clim Past

The ‘Green Sahara’ problem….. still a problem

Quaternary modelling case studies

Modelling improving due to inclusion of additional processes, but current state of the art models as yet untested….(see PMIP3!)

Many problems still remain, e.g. Green Sahara at 6k, cold Western European temps at 21k, not to mention carbon cycle!

Hierarchy of models can be used to address different problems…but ultimate test must be with GCMs