Climate Modelling Group
School of Earth and Ocean Sciences


1. Name of Theme Leader, Department, Institution

Andrew J. Weaver, School of Earth and Ocean Sciences, University of Victoria

2. Title of Project or Theme Area

Paleoclimatic experiments using coupled atmosphere ocean models

3. Co-investigators, Department, Institution

Andrew Bush, Department of Earth and Atmospheric Sciences, University of Alberta

4. Budget

Amount ($) Recommended by Science Committee

Amount ($) Approved by Management Committee

1Cash ($) from Partners

Total NSERC ($) Spent

Year 1

$100,500

$120,000

2$1,955

$100,500

Year 2

$100,444

$120,000

3$33,226

$100,444

Year 3

TBA

$120,000

TBA

TBA

Year 4

TBA

$120,000

TBA

TBA

Year 5

TBA

$120,000

TBA

TBA

1Note, IBM under their Shared University Research program gave A. Weaver an SP2 with 6 nodes and a switch (list price $565,000) for CSHD and related research.

2UVic faculty research and travel award for CSHD research

3UVic faculty research and travel award ($1,726) and grant (including 30% overhead and salary support for M. Eby) from Lawrence Livermore National Laboratories (LLNL – $31,500) to bring A. Weaver’s reduced sabbatical salary to regular level – both are for CSHD research.

5. Progress toward achievement of the objectives described in the original application

Substantial progress towards the goals of CSHD 5 has been made over the first two years of funding. The UVic coupled model has been significantly improved (now at Version 2.0) and is publicly available at http://wikyonos.seos.uvic.ca/climate-lab/model.html. These improvements, implemented by M. Eby, C. Bitz, M. Holland, M. Yoshimori and H. Wang (LLNL) include the development and testing of an elastic-viscous-plastic dynamical sea ice model with multi-level thermodynamics, and an ice thickness distribution; the incorporation of a snow model; the inclusion of an option to rotate the grid to alleviate problems associated with converging meridians at the poles; the inclusion of topography on land which improves the geographical distribution of precipitation and allows us to use realistic river drainage basins; the inclusion of a more complicated river model; the inclusion of advection of moisture. The Marshall/Clarke UBC ice sheet model has also been incorporated into the UVic coupled model. In collaboration with K. Caldeira and P. Duffy at LLNL, we will be incorporating an ocean carbon cycle and we will also include a land surface model (BIOME 3) in the near future. We are currently parallelising all components of our coupled model in collaboration with P. Elgroth at LLNL. We anticipate that the parallel version of the code will be available (as Version 3.0) in January 2000. Our goal is to develop a comprehensive Earth System Clmate Model with which to analyse the causes and consequences of northern hemisphere glaciation.

Version 1.0 of the UVic coupled model was used to investigate the climate of the last glacial maximum (LGM) and the competing effects of CO2, orbital forcing and ice sheet albedo. Tropical LGM temperatures were found to be slightly colder than CLIMAP, but only ~2.2°C less than the present, consistent with a low-mid climate sensitivity to radiative perturbations. An amplification of the cooling occurs in the North Atlantic through a weakening and shallowing of the conveyor. A sensitivity analysis to the strength of the present-day conveyor revealed that changes in ocean circulation do not contribute to global mean LGM cooling.

The most common method used to evaluate climate models involves spinning them up under perpetual present-day forcing and comparing the model results with present-day observations. This approach ignores any potential long term memory of the model ocean to past climatic conditions. We examined the validity of this approach through the 6000 year integration of version 1.0 of the UVic coupled model. The coupled model was initially spun-up with atmospheric CO2 concentrations and orbital parameters applicable for 6 kyr BP. The model was then integrated forward in time through to 2100. Results from this transient coupled model simulation were compared with the results from two additional simulations, in which the model was spun up with perpetual 1850 (preindustrial) and 1998 (present-day) atmospheric CO2 concentrations and orbital parameters. This comparison lead to substantial differences between the equilibrium climatologies and the transient simulation, even at 1850 (in weakly ventilated regions), prior to any significant changes in atmospheric CO2. When compared to the present-day equilibrium climatology, differences were very large: the global mean surface air and sea surface temperatures were ~0.5°C and ~0.4°C colder, respectively, deep ocean temperatures are substantially cooler, southern hemisphere sea ice cover is 38% larger, and the North Atlantic conveyor 16% weaker in the transient case. These differences were due to the long timescale memory of the deep ocean to climatic conditions which prevailed throughout the late Holocene, as well as to its large thermal inertia. We are currently rerunning these experiments using Version 2 of the UVic model (with its more sophisticated representation of sea ice) and we are also including changes in solar forcing.

As noted above the UBC dynamical ice sheet model has been coupled into Version 2 of the UVic coupled model. Experiments and sensitivity analyses have been conducted to address: 1) model validation with present-day, 11 kyr BP, and 21 kyr BP forcing; and 2) the ice sheet response under the competing effects of both orbital and CO2 forcing. Before coupling the ice sheet model, we integrated the UVic model for 2,000 years until a quasi-steady state was reached. Thereafter, we integrate the climate model for 10 years, average the fields (net surface accumulation) over this period and pass them to the ice sheet model as a boundary condition. The ice sheet model is then integrated for 2,000 years with a 10 year time step and the averaged fields are returned to the climate model. This cycle is repeated until the ice sheet model reaches steady state.

The model performs well under present-day, 11 kyr BP and 21 kyr BP forcing. From a serious of sensitivity analyses we concluded that both orbital and CO2 forcing have an impact on ice sheet maintenance and deglacial processes. Although neither acting singly is sufficient to lead to complete deglaciation, orbital forcing seems to be more important. The impact of CO2 has its peak in winter time through changing the rate of deepwater formation and hence poleward ocean heat transport while that of orbital forcing has its peak in summer time at 11 kyr BP and 21 kyr BP. Since the summer time temperature seems dominant rather than winter time temperature, orbital forcing has a larger impact on the ice sheet mass balance than CO2. Also, warm winter time SSTs due to increased CO2 during the deglaciation might contribute to ice sheet mass balance as a negative feedback through slightly enhanced precipitation.

A very challenging and outstanding problem concerning our inability to capture glacial inception 116 kyr BP remains. Since one of our goals is to determine whether or not the closure of the Isthmus of Panama was responsible for the onset of northern hemisphere glaciation ~3 Ma, it is very important that we attempt to resolve the glacial inception issue at 116 kyr BP. In order to address why our model (as do others) does not capture glacial inception we are taking two approaches. In the first, we are determining whether or not our simple atmosphere is missing some important process. As such, several equilibrium experiments have been conducted under past atmospheric CO2 and orbital conditions. The resulting SST and sea ice mask fields have been passed to the CCCma atmospheric GCM, to see whether or not they lead to the presence or absence of perpetual snow cover in northern middle to high latitudes. In the second approach we are attempting to determine whether certain feedbacks are missing in our model that are necessary for us to capture glacial inception. We are now including land surface and carbon cycle (in collaboration with researchers at LLNL) models as well as a parameterisation for cloud feedbacks, with the goals of developing a comprehensive Earth System Climate Model.

With respect to the first approach, the UVic coupled model was integrated to equilibrium under present day and 116 kyr BP orbital parameters and atmospheric CO2 levels. Monthly SST, sea ice thickness and mask fields obtained from these equilibrium simulations were then passed to the CCCma AGCM. Three initial tests (1: present day orbital forcing, present-day UVic coupled model SST/sea ice fields, 350 ppm CO2; 2: 116 kyr BP orbital forcing, present-day UVic coupled model SST/sea ice fields, 240 ppm CO2; 3: 116 kyr BP orbital forcing, 116 kyr BP UVic coupled model SST/sea ice fields, 240 ppm CO2) were conducted with the CCCma AGCM. Preliminary results are extremely encouraging in that there is a clear sensitivity to the ocean SSTs regions critical to glacial inception (e.g. Baffin Island, Kewatin, Labrador Plateau). M. Yoshimori, the PhD student working on this project, is currently writing up these results in collaboration with A. Weaver, N. McFarlane (CSHD 8) and C. Reader (CSHD 3).

A. Bush completed a hierarchy of numerical simulations for the early- to mid- Holocene (9 kyr and 6 kyr BP time slices). These simulations have ascertained that in determining the strength of the south Asian monsoon (for which there is a wealth of proxy data), tropical Pacific SST forcing can actually dominate orbital forcing. These simulations directly address the hypothesis that a permanent El Niño state existed 11K-5K BP and suggest that La Niña conditions were more likely. The hierarchy of simulations culminated in a coupled atmosphere-ocean simulation for 6 kyr BP. The coupled model results support inferences made from the atmosphere-only simulations that La Nina conditions were more likely: a stronger Walker circulation, associated with increased seasonality, produces colder Pacific SSTs by altering the morphology of the tropical thermocline. Since the publication of these results, proxy data from the Galapagos islands have revealed La Niña-like conditions in the early-mid Holocene (Reidinger, personal communication).

A coupled atmosphere-ocean simulation for the LGM has been completed with the GFDL model. Tropical SST cooling of up to 6°C was simulated in the equatorial Pacific Ocean and was shown to be a result of changes in strength of the dynamical and thermodynamical atmosphere-ocean interactions that regulate the depth of the tropical Pacific thermocline. These results describe mechanisms that can lead to the tropical temperature depressions of 5-6° that have been inferred from a variety of proxy data. We are linking these numerical results directly to the geological record through data produced by N. Rutter’s group (CSHD 9). Examination of changes in monsoon strength and direction at both 6 kyr BP and the LGM are being collated in order to compare simulated movement of the Gobi desert margin to that inferred from the Chinese loess records.

6. Problems Encountered

None

7. Training of Research Personnel

A. Weaver is presently supervising 2 MSc students, 6 PhD students. In January 2000, his group will be joined by Katy Hill (MSc student) and Melanie Cottet-Puinel (PhD student). Olaf Dravnieks, who recently defended his MSc thesis, will leave his group by this time. In the tables below, we have highlighted in bold those students/research associate who either are/were working or will work on CSHD projects.

Student

Degree

Country

Area

Student

Degree

Country

Area

L. Waterman

MSc

Australia

Arctic

F. McLaughlin

PhD

Canada

Arctic

O. Dravnieks

MSc

Canada

Ocean mixing

M. Roth

PhD

Canada

Ocean Modelling

K. Hill

MSc

England

CSHD

M. Cottet-Puinel

PhD

France

CSHD

T. Ewen

PhD

Canada

CSHD

M. Yoshimori

PhD

Japan

CSHD

G. Arfeuille

PhD

France

Arctic

D. Stone

PhD

Canada

Climate Variability

Of the three students that have graduated over the last two years, one was funded by CSHD. Gary Clarke was her external examiner. Upon graduation, P. Poussart received the UVic Lieutenant Governor’s Silver Medal as the top graduating MSc student. She is currently a PhD student working with Dr. D. Schrag at Harvard University.

MSc (Year)

Present Affiliation

MSc (Year)

Present Affiliation

E. Wiebe (1998)

Systems Analyst, University of Victoria

P. Poussart (1999)

PhD Student, Harvard University

D. Stone (1999)

PhD Student, University of Victoria

   

A. Weaver currently supervises two research associates. Marika Holland and Cecilia Bitz both recently returned to the US after two years as research associates in his group. They were responsible for the implementation of the new sea ice model in the UVic coupled model. Andreas Schmittner and Katrin Meissner will arrive in January to work on CSHD topics and Harper Simmons will arrive in March, 2000.

Research Associate

Country

Area

Research Associate

Country

Area

M. Eby

Canada

CSHD

H. Simmons

USA

Arctic

E. Wiebe

Canada

Computing

M. Holland

USA

Arctic

A. Schmittner

Switzerland

CSHD

C. Bitz

USA

Arctic/CSHD

K. Meissner

Germany

Arctic

     

8. Partnerships and Collaboration

The CSHD project has allowed A. Weaver to develop the most stimulating and productive collaborations he has ever had the opportunity to be involved in. Masakazu Yoshimori, an outstanding PhD student, has coupled the Marshall/Clarke UBC Ice Sheet Model into the UVic coupled model to investigate the causes and consequences of northern hemisphere glaciation. G. Clarke’s group (CSHD 1) and our group (CSHD 5) frequently interchange models, output and discussions and we have arranged a number of meetings between us. M. Yoshimori has also facilitated a close collaboration with N. McFarlane (CSHD 8) and C. Reader (CSHD 3) through a novel approach at conducting paleoclimate modelling simulations. Specifically, the UVic model is run to equilibrium to provide the CCCma AGCM a lower boundary condition SST field. The CCCma AGCM is then run in stand-alone mode within a paleo context.

M. Cottet-Puinel will arrive from France in January 2000 to work with A. Weaver’s group and the groups lead by C. Hillaire-Marcel (CSHD 6) and A. De Vernal (CSHD 2). As an undergraduate student she already worked with C. Hillaire-Marcel and since that time she has gained modelling skills working with B. Barnier in France. Finally, I co-authored a review article with N. Rutter (CSHD 9) on the Younger Dryas.

Internationally, A. Weaver has developed a very strong collaboration with P. Duffy and K. Caldeira at Lawrence Livermore National Laboratories. T. Ewen will be visiting LLNL in January to couple K. Caldeira’s ocean carbon cycle model into the UVic coupled model. The UVic coupled model is now also being used by a number of other researchers internationally (Canada: UBC, IOS, McGill; Chile: University of Concepcion; China: Nanjing University: Croatia: Marine Meteorological Centre; Germany: University of Bremen; Japan: Hokkaido University; Korea: Seoul National University; UK: University of East Anglia; USA: LLNL, NCAR, University of Maryland, Pennsylvania State University, University of Washington).

Publications Arising (1998—1999): A. Weaver

a) CSHD Funded Publications:

1. Weaver AJ, M Eby, AF Fanning, EC Wiebe, 1998: Simulated influence of carbon dioxide. orbital forcing and ice sheets on the climate of the last glacial maximum. Nature, 394, 847—853.

2. Weaver AJ, C Green, 1998: Global climate change: Lessons from the past – policy for the future. Ocean & Coast. Manag., 39, 73—86.

3. Weaver AJ, CM Bitz, AF Fanning, MM Holland, 1999: Thermohaline circulation: High latitude phenomena and the difference between the Pacific and Atlantic. Ann. Rev. Earth Plan. Sci., 27, 231—285.

4. Poussart PF, AJ Weaver, CR Barnes, 1999: Late Ordovician glaciation under high atmospheric CO2: A coupled model analysis. Paleoceanogr., 14, 542—558.

5. Weaver AJ, 1999: Millennial timescale variability in ocean/climate models. In: Mechanisms of Global Climate Change at Millennial Time Scales. Webb RS, PU Clark, & LD Keigwin Eds., AGU, Geophys, Mon. 112, Washington, D.C., pp. 285—300.

6. Rutter NW, AJ Weaver, D Rokosh, AF Fanning, DG Wright, 1999: Is the Younger Dryas a global event? Can. J. Earth Sci., in press.

7. Flato GM, GJ Boer, NA McFarlane, D Ramsden, MC Reader, AJ Weaver, 1999: The Canadian Climate Centre for Climate Modelling and Analysis global coupled model and its climate. Clim. Dyn., submitted.

8. Wang H, PB Duffy, K Caldeira, M Eby, AJ Weaver, AF Fanning, 1999: Importance of water vapor transport to the hydrological cycle in an atmospheric energy-moisture balance model coupled to an OGCM. J.Geophys. Res., submitted.

9. Bitz CM, MM Holland, M Eby, AJ Weaver, 1999: Simulating the ice-thickness distribution in a coupled climate model. J.Geophys. Res., submitted.

10. Weaver AJ, PB Duffy, M Eby, EC Wiebe, 1999: Evaluation of ocean and climate models using present-day observations and forcing. Atmos.-Ocean, in press.

b) Other Publications (1998—1999):

11. Weaver AJ, S Valcke, 1998: On the variability of the thermohaline circulation in the GFDL coupled model. J. Clim., 11, 759—767.

12. Fanning AF, AJ Weaver, 1998: Thermohaline variability: The effects of horizontal resolution and diffusion. J. Clim., 11, 709—715.

13. Giorgi F, GA Meehl, A Kattenberg, H Grassl, JFB Mitchell, RJ Stouffer, T Tokioka, AJ Weaver, TML Wigley, 1998: Simulation of regional climate change with global coupled climate models and regional modeling techniques. In: The Regional Impacts of Climate Change, An Assessment of Vulnerability. Watson RT, MC Zinyowera, & RH Moss Eds., Cambridge University Press, Cambridge, England, pp. 427—437.

14. National Research Council, 1999: Global Ocean Science: Toward an Integrated Approach. National Academy Press, Washington, D.C., 165pp.

15. Weaver AJ, 1999: Extratropical subduction and decadal modulation of El Niño. Geophys. Res. Lett., 26, 743—746.

16. Huck T, A Colin de Verdière, AJ Weaver, 1999: Interdecadal variability of the thermohaline circulation in box-ocean models forced by fixed surface fluxes. J. Phys. Oceanogr., 29, 893—910.

17. Huck T, AJ Weaver, A Colin de Verdière, 1999: On the influence of the parameterisation of lateral boundary layers on the thermohaline circulation in coarse-resolution ocean models. J. Mar. Res, 57, 387—426.

18. Duffy PB, M Eby, AJ Weaver, 1999: Effects of sinking of salt rejected during formation of sea ice on results of a global ocean-atmosphere-sea ice climate model. Geophys. Res. Lett., 26, 1739-1742.

19. Wiebe EC, AJ Weaver, 1999: On the sensitivity of global warming experiments to the parametrisation of sub-grid scale ocean mixing. Clim. Dyn., in press.

20. Weaver AJ, EC Wiebe, 1999: On the sensitivity of projected oceanic thermal expansion to the parameterisation of sub-grid scale ocean mixing. Geophys. Res. Lett., in press.

21. Duffy PB, M Eby, AJ Weaver, 1999: Climate model simulations of effect of Antarctic sea ice on stratification of the Southern Ocean. J. Clim., submitted

22. Holland MM, AJ Brasket, AJ Weaver, 1999: The impact of rising atmospheric CO2 on low frequency North Atlantic climate variability. Geophys. Res. Lett., submitted.

23. Holland MM, CM Bitz, M Eby, AJ Weaver, 1999: The role of ice ocean interactions in the variability of the North Atlantic thermohaline circulation. J. Clim., submitted.

24. Stone DA, AJ Weaver, FW Zwiers, 1999: Trends in Canadian precipitation intensity. Atmos.Ocean, submitted.

Publications Arising (1998—1999): A. Bush

a) CSHD Funded Publications:

Bush ABG and S.G.H. Philander, 1998: The role of ocean-atmosphere interactions in tropical cooling during the Last Glacial Maximum. Science, 279, 1341-1344.

Campbell ID, C Campbell, MJ Apps, NW Rutter, ABG Bush, 1998: Late Holocene ~1500 yr. climatic periodicities and their implications. Geology, 26, 471-473.

Bush ABG, 1999: Assessing the impact of mid-Holocene insolation on the atmosphere-ocean system. Geophys. Res. Lett., 26, 99-102.

Bush ABG, SGH Philander, 1999: The climate of the Last Glacial Maximum: Results from a coupled atmosphere-ocean general circulation model. J.Geophys. Res., in press.

Bush ABG, 1999: A positive feedback mechanism for Himalayan glaciation. Quat. Int., in press.

Bush ABG, 1999: Orbital forcing versus sea surface temperature forcing and the implications for early Holocene climate. Quat. Res., submitted.

b) Other Publications (1998—1999):

Masina S, SGH Philander, ABG Bush, 1999: An analysis of tropical instability waves in a numerical model of the Pacific Ocean. Part II: Generation and energetics of the waves. J.Geophys. Res., in press.


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