Understanding Paleoclimates ~ Modelling the Glacial/Interglacial Climate with Coupled GCM~

Transcription

1 Understanding Paleoclimates ~ Modelling the Glacial/Interglacial Climate with Coupled GCM~ Ayako Abe-Ouchi, CCSR, University of Tokyo / FRSGC 1 Introduction 2 Model description 3 Greening Sahara (mid Holocene) 4 Glacial Ocean 5 Ice sheet evolution 6 Summary

2 Introduction Earth System Modelling for Climate in the Past (Paleoclimate) --- To Understand the climate behaviour --- To validate the GCM that we use for Future prediction Model for Paleoclimate ---> 1 needs long integration ---> 2 needs feedback loops among several subsystems. ---> 3 needs high resolution if the phenomenon is regional. Preliminary results are presented

3 Model description Atmosphere :CCSR/NIES/FRSGC AGCM T42L20 (? simple EMBM) Ocean: CCSR COCO 1~0.5 lat x 1.4lon, L43 Sea ice : Elastic Viscous Plastic model with 0 layer thermodynamics. Ice Sheet: Three dimensional thermo-mechanical coupled model Dynamical Vegetation: to be coupled (LPJ and Kissme) Carbon Cycle: to be coupled

4 Surface Temperature in Coupled GCM SST Model -Obs. 1 8 Air Temperature (2m) 16? CO2 1%/yr 16 Model AfterSST 70 years Model -Obs. CT *Low-Mid latidude: drift occurs in the first few years (fast initial response) *High latitude drift appears after the initial drift. ObservationCT02603 Model After 70 years

5 Precipitation Obs. ( CMAP) CGCM DJF DJF JJA AGCM

6 Greening Sahara Polen ( Hoelzmann et al., 1998 ) Savanah Steppe Not enough sensitivity of model climate of AGCM only. ---> PMIP2

7 Sea Surface Temp. Change and Monsoon at 6000 yr BP

8 Precipitation Change in Coupled GCM (zonal mean 20W-30E) 300 CGCM Slab AGCM 200 Coupled GCM 100 drain (mm/year) Climatology affects The response of the 0 Rain belt Rain (20W-30E) 2000 CGCM 0ka Slab 0ka AGCM 0ka Observation mm/year Latitude

9 Modification of Physical Processes in AGCM 2500 AGCM 0ka NEW 0ka Observation mm/year 1000 MCB6k OLD Latitude Modification in AGCM physics; moistenning the troposphere improved the response Chikira 2003 Trop. Rain Forest Steppe Biome (Prentice et al., 199 Savanna Dessert

10 4. Glacial Ocean and climate Response of surface ocean and thermohaline circulation to external condition is of interest. Ice age climate can be checked by rich data. Carbon cycle which involves the surface and deep sea could be related to the low CO2. Ice Age data show a large climate variabilty. (Modification of ENSO be discussed.) Without flux adjustment and some spin-up technique Control Experiment vs. Low CO2 Experiment Is conducted.

11 Time series of Thermohaline circulation Control CO2x2 Glacial CO2

12 Overturning (THC) in the North Atlantic Glacial 14 Control 8 7 Antarctic Bottom Water dominating more in the Glacial than the Control.

13 Ocean Heat Transport Present (Red line) vs. Glacial World (Blue dashed line) 1.5 PW latitude 90 More heat to the south and less heat to the North at the Glacial.

14 Formation of NADW and Sea Ice in North Atlantic Modern Glacial Winter (Feb.) : Convection in the north of Iceland disappears in Glacial Ocean

15 Formation of NADW and Sea Ice in North Atlantic (2) Future Warming Modern Glacial Winter (Feb.) : Convection in the north of Iceland disappears in Glacial Ocean

16 5. Ice Sheet Evolution Why did glacial/interglacial cycle of 100 ka cycle occur? ---> Oscillator of 100 ka? (CO2, eccentricity.) ---> cc. 20 ka, 40 ka oscillator - resonance or nonlinearity of the system? ---> 100ka forcing phase locked some oscillator Wavelet Analysis (Hargreaves and Abe-Ouchi 2003)

17 Phase diagram of a simple model response to periodic forcing of 20ka (Abe-Ouchi, 1995) Forcing 2000 )1800 m (1600 A1400 L E Response 1500 e z i1000 S e c I ( Ma ) )8 m (6 ed u ti 4 l p m2 A 0 Small Ice Cap Non-linear Response A Climatic trajectory Permanent Ice No Ice cooler warmer Mean of ELA (100m)

18 Ice Sheet Model in ESM CCSR/NIES/ AGCM monthly mean Temperature and Precipitation Ice thickness, Bedrock sinking Ice temp. and flow 3D thermo-mechanical ice sheet model (Saito and Abe-Ouchi, 2002) Shallow ice approximation Thermodynamics-dynamics coupling Simple sliding applied Bedrock isostacy included Horizonal resolution 1 deg lon./lat. Vertical 20 layers

19 Temp.(JJA) and Net Mass Balance of LGM Snowfall/ Sublim./ Melt / Net (mm/year) Laurentide Fennoscan

20 Ice sheet - atmosphere feedback Ice albedo feedback Elevation - mass balance feedback Stationary wave feedback (through temperature) (Cook and Held, 1988) Transient eddy feedback (through precipitation) (Hall et al, 1990, Kageyama and Valdes, 1997)

21 Total cooling Cooling due to Ice Sheet Existence Temperature drop (K) Control minus LGM Albedo Effect Lapse rate effect Residual

22 Stationary eddy- Temperature feedback? (Full - Flat ice LGM assuming lapse rate of 5 K/ km) 500hPa Z(m) (JJA) Temperature change (K) At 850hPa (JJA)

23 Ice Sheet Modelling using the AGCM results at LGM (a) No Ice LGM without ice sheet feedbacks (b) Albedo effect But no lapse rate effect (c) Only lapse rate effect (d) Albedo effect + lapse (e) Full LGM rate effect

24 Ice Sheet Size Dependence of net ice mass balance on ice sheet size Ic e C LGM 21 ka ap 18 ka 15 ka No Ice LGM Forcing 12 ka

25 Dependence of ice sheet budget on forcing : CO2 vs orbital ~ Grill the LGM ice sheet by different forcing Experiments with Cold vs Hot orbit e=0.05 Cool vs Warm orbit e= CO2 low = 200 ppm Pre-Ind. = 280 ppm high = 345ppm

26 Dependence of net ice mass balance on CO2 and orbital forcing Cold orbit &Low CO2 0 Cold orbit &High CO Hot orbit &Low CO Hot orbit &High CO

27 Ice SheetAtm-Ocean coupling Response to Orbital parameters (warm-cool o With Ice Sheet Without Ice Sheet Ice topo. Air Temp. JJA Ocean.

28 Summary Climate Change could be affected by the model control climate. Careful consideration of moisture process affects the whole paleoclimate discussion. ES enables the long term integration and a lot of experiments for the past climate. Different Hierarchy of models should be used. GCM could help the simpler model to identify the processes that should be included with higher priority.

29 Conclusion (2) Laurentide do help the Fennoscandian ice sheet to grow in the western part through the transient eddy feedback. Growth of Fennoscandinan ice sheet to the south in the western part is prevented by the stationary wave feedback of Laurentide ice sheet and the presence of itself.

30 Summary 1. Phase diagram of ice sheet response to periodic forcings of 20ka show that the100 ka-like response occurs in a certain range of phase space of forcing. 2. Especially the summer maxima of this mode locates in a limited range, which corresponds to the area of multiple equilibria. 3. In case of Laurentide ice sheet, multiple equilibria seems to exist even under the LGM forcing. Threshold of ice sheet size/shape is between 15 and 18 ka ice size. 4. It is likely that the response time in this area of multiple equilibria can become very long under certain environmental condition, such as the climatic forcing and bedrock response. 5. The speed of growth and retreat of ice sheet could be highly dependent on the strength of feedbacks. 6. Orbital forcing may have a larger impact on ice sheet than

31 Conceptual threshold model for the glacial-interglacial cycles. - The termination always following the smallest maxima in summer insolation but always follow the smallest maxima in A summer insolation -A model able to switch abruptly (Paillard, 1998) between different climatic modes, in relation to both astronomical forcing and ice sheet evolution. Thresholds (for both insolation and Ice volume) and time constants are important. For each mode, the ice volume equation is linear,

32 Simulation of NH ice volume under both the insolation and CO2 change Berger et al (1998), Li et al (1998) -Successful simulation of ice volume by an EMIC. (2D- lat.and vertical) -Sensitivity of NH ice to CO2 is not constant. -Relative importance of CO2 vs. Orbit depends on model. (cf, Tarasov and Peltier, 1997)

33 This talk Here we focus first on a single oscillator as an example and show the possibility of producing 100ka -like oscillation (longer than the one of forcing) by a realistic ice sheet model. Several sensitivity studies are performed also by GCM. Response of ice sheet to periodic forcing by a 2-dim ice sheet model. The thresholds and response time in GCM for Laurentide ice sheet to understand the termination mechanism.

34 Temperature change (K) over Laurentide ice sheet (K) Annual mean Summer (JJA) SST and CO2 effect Ice Ice Albedo topograeffect phy effect Total Present - LGM

35 Topography Effect upon Cooling From the exps. of Full LGM - Flat ice LGM run, Lapse rate of 5 K/ km is estimated. Residual is the component that Cannot be explained by the change assuming the lapse rate. Lapse rate effect Residual (K)

36 Precipitation change rate from Full, flat, no ice LGM runs (a) Full LGM (b) Albedo Effect (c) Topography Effect

37 Response of ice sheet to periodic forcing of 20 ka in a 2-D ice sheet model

38 Equilibria of ice sheet and the phase diagram Range of summer maxima for chaotic response 10 )8 m 00 1( 6 ed ut 4 il p m2 A 0 Small Ice Cap Non-linear Response A Climatic trajectory Permanent Ice No Ice cooler Mean of ELA (100m) warmer 24

39 Inception and Ice sheet growth Ice sheet can initiate with the help of small scale topography (~ 50km size). Abe-Ouchi and Blatter (1993)

40 Uniform 6K cooling With altitude + albedo feedback. ± ̃sƒNƒ`ƒƒ ðœ é ½ ß É Í A gquicktimeþ \Šg Æ A ggif h L ƒvƒ ƒoƒ ƒ ª K v Å B

41 Effect of Strength of Feedbacks on ice sheet evolution and Equilibria LGM forcing Uniform 6K cooling With only altitude feedback. Uniform 6K cooling With altitude + albedo feedback. Strength of the Albedo feedback controls both the final equilibrium state and the speed reaching a certain size (time constant).

42 Equilibria of ice sheet and the phase diagram Range of summer maxima for chaotic response 10 )8 m 00 1( 6 ed ut 4 il p m2 A 0 Small Ice Cap Non-linear Response A Climatic trajectory Permanent Ice No Ice cooler Mean of ELA (100m) warmer 24

43 Retreat speed (Time constant?) Retreat speed of the ice sheet is highly dependent on the forcing change (a, b and c) and the delay of bedrock response.

44 Ice Sheet Size Threshold/ Critical Ice sheet size and shape Around the threshold, the Ic e C ap relative relation between the current ice sheet size and the ice sheet size at the threshold becomes critical. The response time of ice sheet could be very large or small. No Ice LGM Forcing

45 Impact of ice sheet size upon climate Difference in summer air temperature 12ICE-LGM 15ICE-LGM

46 ????????????????

47 Ice Sheet Size Threshold/ Critical Forcing Ic e C ap Around the threshold, any small forcing can push the ice sheet into a new mode. current No Ice Forcing

48 Dependence of net ice mass balance on CO2 and orbital forcing(2) CO2 200-> 280ppm 39.8 mm/yr CO2 200-> 345ppm 84.8 mm/yr Orbit e = mm/yr (cool to warm) e = mm/yr (cold to hot) Orbit

49 Summary Green Sahara Glacial Ocean Ice

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51 Around the threshold the response time of ice Sheet is very large.

52 Response of climate to orbital parameters Suarez and Held (1978)

53 ± ̃sƒNƒ`ƒƒ ðœ é ½ ß É Í A gquicktimeþ \Šg Æ A ggif h L ƒvƒ ƒoƒ ƒ ª K v Å B

54 ????????

55 Conceptual threshold model for the glacial-interglacial cycles.(palliard, 1998) -The termination always follow the smallest maxima in summer insolation. - Importance of thresholds and time constants for each mode.

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58 Sahara??

59 Conclusion (2) Laurentide do help the Fennoscandian ice sheet to grow in the western part through the transient eddy feedback. Growth of Fennoscandinan ice sheet to the south in the western part is prevented by the stationary wave feedback of Laurentide ice sheet and the presence of itself.

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61 Mode of Glacial/Interglacial cycles and the role of ice sheet Why did glacial/interglacial cycle of 100 ka cycle occur? ---> Oscillator of 100 ka? (CO2, eccentricity.) ---> cc. 20 ka, 40 ka oscillator produces nearly 100ka cycle through some mechanism of resonance or nonlinearity of the system. ---> 100ka forcing phase locked some oscillator