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

1. Earth system models of intermediate complexity:Examining the past to understand the future Future Challenges for Marine Sciences in Canada 40th Anniversary Symposium Bedford Institute of Oceanography 24-25 October 2002 Andrew Weaver School of Earth & Ocean Sciences University of Victoria

2. 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

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

4. The old vision of climate models: The EMIC vision of climate models: 1. Bern 2.5D 2. CLIMBER-2 3. EcBilt 4. EcBilt-CLIO 5. IAP RAS 6. MPM 7. MIT 8. MoBidiC 9. PUMA What EMICs exist: 10. UVic 11. IMAGE 2 What are earth system models of intermediate complexity?

5. 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

6. The 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

7. The UVic Coupled Model 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

8. The UVic Coupled Model 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

9. Northern Hemisphere Southern Hemisphere Continental Ice Sheet Component The UVic Coupled Model MODEL OBSERVED Comparison between observed and simulated present day northern and southern hemisphere ice sheets

10. The UVic Coupled Model 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

11. The UVic Coupled Model 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.

12. MODEL NCEP REANALYSIS Preindustrial (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 The UVic Coupled Model 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%

13. The UVic Coupled Model Atmospheric Component — A dynamic energy-moisture balance model The 32 river drainage basins used in the UVic model.

14. The UVic Coupled Model The wind feedback ECMWF Reanalysis (45°N): Near-surface air density vs near surface air temperature ECMWF Reanalysis (thick lines); NCEP Reanalysis (thin lines): Latitudinal variation of parameters a and b in r = a + b t

15. The UVic Coupled Model Evaluation of the wind feedback using CCCma AGCM fields Zonal mean zonal wind velocity Zonal mean meridional wind velocity Geostrophic (frictional near equator) wind anomalies for 2 x CO2. Red: ECMWF Reanalysis Green: NCEP Reanalysis Black: CCCma AGCM

16. The UVic Coupled Model 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

17. Surface Air Temperature Sea Surface Temperature Sea Surface Salinity The UVic Coupled Model — Climatology

18. The UVic Coupled Model — Climatology Atlantic Meridional Overturning(Sv; 1Sv=106m3s–1) Global Meridional Overturning (Sv; 1Sv=106m3s–1)

19. Northern Hemisphere SUMMER WINTER Southern Hemisphere Sea Ice Climatology The UVic Coupled Model

20. Release in North Atlantic Release in North Pacific Release in Weddell and Ross Seas Age Tracer Water Mass Analysis The UVic Coupled Model Location of tracer release 27°W

21. The Climate of the 20th Century

22. Focus of rest of talk Climate Change over the Last Glacial Cycle Dansgaard-Oeschger Oscillations and Heinrich Events

23. UVic Model CLIMBER-2 CCCma CGCM2 Climate Change over the Last Glacial Cycle The Last Glacial Maximum

24. Seidov et al. (1996) De Vernal et al. (2000) Seidov et al. (1996) LGM rate: 11 Sv LGM_ADV_1A rate: 14 Sv De Vernal et al. (2000) LGM PD_FWF rate: 25 Sv LGM_ADV_1 rate: 4 Sv Correlation and basin average error for several realisations of NADW formation in UVic model What NADW overturning rate are LGM proxy reconstructions consistent with? Schmittner, Meissner, Eby, Weaver, 2002: Paleoceanography, in press Present day overturning rate: 21 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

25. The Hysteresis of the North Atlantic Overturning Meissner, Schmittner, Weaver, Adkins, 2002: Paleoceanography, in press Experimental set up for Analysis

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

27. Proxy record + error bars Intersection: model/proxy Interpolation between equilibria Meissner, Schmittner, Weaver, Adkins, 2002: Paleoceanography, in press What NADW overturning rate are LGM proxy reconstructions consistent with? NADW: 12.7–18.3 SV

28. Climate Change over the Last Glacial Cycle Dansgaard-Oeschger Oscillations and Heinrich Events Schematic diagram taken from: Alley, 1998: Nature,392, 335 - 337

29. Sample metastable stadial state Interstadial state Present Day: Red Glacial: Black 2 Stable equilibria 2 Stable equilibria + metastable regime with < 10 Sv Stability of the thermohaline circulation using fully interactive ice sheet Schmittner, Yoshimori, Weaver, 2002: Science, 295, 1489–1493 Investigate Hysteresis behaviour: Apply linearly varying freshwater perturbation

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

31. Melt of ice sheet Increased calving Growth of ice sheet Dansgaard-Oeschger Oscillations A. Glacial state ice sheet height and calving rate B. Calving rate and mass balance difference immediately after transition from cold stadial to warm interstadial

32. Force the transition from a stadial to an interstadial state Surface mass balance (dashed) and calving rate (solid) Weak sustained evaporation Strong sustained evaporation Difference between mass balance and calving rates (solid); Anomalies in Atlantic surface freshwater balance (dashed) Positive values indicate positive feedback between THC and ice sheet mass balance Response of NADW formation Dansgaard–Oeschger Oscillations

33. 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.

34. The global response to changes in NADW formation rate Surface Temperature Anomaly 500m Temperature Anomaly

35. Assess the effects of shutting off ice berg calving following a 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 Heinrich Events Why an abrupt warming after a Heinrich event?

36. 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 Wood, Keen, Mitchell, Gregory, 1999: Nature, 399, 572–575 • Coupled modelling study using Hadley Centre model 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 • No analogue during last glacial maximum • Shutdown of LSW formation as a consequence of global warming Is there a link between these? Can we understand why?

37. Preindustrial 125 kyr BP LGM Cottet-Puinel, Weaver, Hillaire-Marcel, de Vernal, Clark, 2002: Quaternary Science Reviews, submitted Labrador Sea Water formation over the last glacial cycle

38. 125 Kyr BP Preindustrial Cottet-Puinel, Weaver, Hillaire-Marcel, de Vernal, Clark, 2002: Quaternary Science Reviews, submitted Labrador Sea Water formation over the last glacial cycle

39. August Cottet-Puinel, Weaver, Hillaire-Marcel, de Vernal, Clark, 2002: Quaternary Science Reviews, submitted Labrador Sea Water formation over the last glacial cycle Last Glacial Maximum February

40. A long 21,000 year integration 6 & 12 kyr BP equilibria looked like preindustrial equilibrium NADW at ~6 kyr BP Cottet-Puinel, Weaver, Hillaire-Marcel, de Vernal, Clark, 2002: Quaternary Science Reviews, submitted Labrador Sea Water formation over the last glacial cycle

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

42. Cold start 1%/year at 2100 Cold start 2%/year at 2100 Warm start at 2100 The future of Labrador Sea Water formation? The transient response at year 2100

43. The future of Labrador Sea Water formation? The quasi-equilibrium response at year 2700 Cold start 1%/year at 2700 Cold start 2%/year at 2700 Warm start at 2700

44. 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

45. Summary and Conclusions In 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 the salt oscillator mechanism 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

46. 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

47. 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.