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Quaternary modelling case studies 1)Last Glacial Inception : ~115kyrBP 2)Last Glacial Maximum : ~21kyrBP 3)The mid-Holocene : ~6kyrBP.

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Presentation on theme: "Quaternary modelling case studies 1)Last Glacial Inception : ~115kyrBP 2)Last Glacial Maximum : ~21kyrBP 3)The mid-Holocene : ~6kyrBP."— Presentation transcript:

1 Quaternary modelling case studies 1)Last Glacial Inception : ~115kyrBP 2)Last Glacial Maximum : ~21kyrBP 3)The mid-Holocene : ~6kyrBP

2 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, , 1999.

3 End of the last interglacial. Initiation of large ice-sheets. Glacial Inception, 115kyrBP 1) Last Glacial Inception

4 Northern and Southern hemisphere ice-sheet volume similar to present. CO 2 similar to pre- industrial modern. Difference: ORBIT! Higher eccentricity and lower obliquity than present, but perihelion unchanged => cooler NH summers! Vettoretti and Peltier, 2004

5 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, , 1993.

6 First modelling studies in 80s fail to simulate inception. Mid-90s, first successful inception experiment. Ocean temperature changes, accuracy of models present-day climate both important. Dong and Valdes, Journal of Climate, 8, , 1995.

7 Ocean circulation changes also important. Khodri et al, 2001

8 Vettoretti and Peltier, 2004

9 Vegetation changes also important. Boreal forest/tundra – snow - albedo feedback. See also de Noblet et al, Geophysical Research Letters, 23, , 1996, Dorman & Sellers 1989 Snowy Forest: low albedoSnowy Tundra: high albedo

10 More recent work includes fully dynamic ice sheet models….but relatively simple EMICs….. Transient simulations Kubatzki et al, Climate Dynamics (2006) 27: 333–344 Kubatzki et al, 2006

11 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

12 Largest mass of land-ice in the last 130,000 years. Last Glacial Maximum, 21kyrBP

13 Incoming solar radiation distribution very similar to present. CO 2 at approx 185ppmv ( pre-industrial 280ppmv, present approx 380ppmv (and rising!)).

14 Last Glacial Maximum, 21kyrBP Observations: global ice-sheet area reconstruction, derived from position of glacial morraines. Modern [fraction]LGM Peltier, Science, 265, , 1994.

15 Last Glacial Maximum, 21kyrBP Observations: global topographic reconstruction, derived from observed rebound of lithosphere. Modern [metres]LGM Peltier, Science, 265, , 1994.

16 Kageyama et al, 2006 ICE-4GICE-5G

17 Last Glacial Maximum, 21kyrBP Observations: global sea-surface temperature: CLIMAP. Derived from bugs, e.g. foraminifera, in ocean sediments. December SST, o C LGM-present CLIMAP project members, Map and chart ser. MC-36, For updated version see also Hostetler and Mix, Nature, 399, , Also, newer MARGO data.

18 Kucera et al, 2005

19 de Vernal et al, 2006

20 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.

21 Last Glacial Maximum, 21kyrBP Observations: terrestrial pollen data. Kageyama et al, Climate Dynamics, 17, 23-43, 2001

22 Last Glacial Maximum, 21kyrBP History of LGM modelling GCMs with constrained (CLIMAP) SSTs and sea-ice extent, constrained (Peltier ICE4G icesheets), constrained CO 2. (PMIP). GCMs with simple ocean (thermodynamic, not dynamic) and seaice, constrained (Peltier ICE4G icesheets), constrained CO 2. GCMs with fully-dynamic ocean and seaice and vegetation, constrained (Peltier ICE5G icesheets), constrained CO 2. (PMIP2). PMIP2 website: PMIP1 website:

23 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.

24 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.

25 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

26 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.

27 Effect of including vegetation changes in the GCM Ramstein et al, Clim. Past, 3, 331–339, 2007

28 Effect of including CO 2 effects on vegetation… Clim. Past, 3, 331–339, 2007

29 Last Glacial Maximum, 21kyrBP Dynamic ocean and seaice Was part of the North Atlantic warmer than present?! Hewitt et al, Climate Dynamics, 20, , 2003

30 IPCC AR4, Paleoclimate Chapter Ensemble does not support warm Atlantic Relative importance of forcings

31 Bracconnot et al, 2007, Clim Past Difference between fully coupled (AO), slab, or fixed SSTs…

32 IPCC AR4, Paleoclimate Chapter Comparison with data

33 Downscaling… Vrac et al, 2007

34 Period of relative warmth. Mid-Holocene, 6kyrBP The mid-Holocene, 6kyrBP

35 IPCC AR4, Paleoclimate Chapter Why study 6k?

36 The mid-Holocene, 6kyrBP Relatively large northern-hemisphere summer insolation (larger obliquity and eccentricity and change in perihelion) CO 2 at approx pre-industrial - 280ppmv.

37 Bracconnot et al, 2007, Clim Past Difference between fully coupled (AO) or fixed SSTs…

38 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) esources/BIOMES_data/BIO ME_v4.2.htm

39 The mid-Holocene, 6kyrBP Intensification of the Asian and African Monsoons See also, Texier et al, Journal of Climate, 13, , However, coupled climate-vegetation models currently unable to generate a green Sahara – not sensitive enough. JJA precipitation change, mm/day,6kyrBP-preindustrial

40 Bracconnot et al, 2007, Clim Past The Green Sahara problem….. still a problem

41 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


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