Climate Modelling Group
School of Earth and Ocean Sciences

Canadian Foundation for Climate and Atmospheric Sciences

Progress Report:

GR-201 – Vegetation/Carbon Cycle Feedbacks on Quaternary Climate

June 19, 2002

1: Principal Investigator

Andrew Weaver

2: Institution

School of Earth & Ocean Sciences, University of Victoria

PO Box 3055, Victoria, BC, V8W 3P6

3: Milestones and progress towards their completion

There were eight milestones as part of this project and we are ahead of schedule in that the model development milestones (1, 2 and 3) are now completed. This will allow us to spend more time on the interesting scientific milestones (4—7) which are not due to be completed until 2003/2004.

Tracy Ewen, a PhD student, has implemented an inorganic ocean carbon cycle model into the UVic ESCM (milestone 1). She used the new version of the model to examine the role of ocean feedbacks in reducing atmospheric CO2 levels if emissions were to be reduced or stopped (see Ewen et al., 2002).

With increased anthropogenic carbon dioxide emitted into the atmosphere, climate feedbacks could potentially reduce further uptake of carbon by the oceans. The most significant feedbacks acting on the system to reduce carbon sequestration by the oceans are reductions in the thermohaline circulation (THC) and increased sea surface temperatures (SSTs). Although changes to the SSTs affect the solubility of atmospheric CO2 across the ocean-atmosphere interface, changes in the strength of the THC lead to more fundamental modifications of ocean circulation and hence transport and storage of carbon to the deep ocean. Using the UVic model, which now incorporates a ocean carbon solubility pump, we examined the evolution of atmospheric carbon dioxide levels under a variety of emissions scenarios. We found a weakening of the THC and increased SSTs in all simulations. Although these positive feedbacks acted on the carbon system to reduce uptake, we found that the ocean had the capacity to take up an additional 65-75% of the atmospheric CO2 increase when anthropogenic forcing was stopped. This reduced by about 5% for each 50 year period that anthropogenic emissions were maintained at a stabilised and elevated atmospheric greenhouse CO2 level.

The results of this work clearly have enormous and encouraging policy implications with respect to future fossil fuel emissions. If we are able to reduce emissions in the near future, there is hope that the ocean can draw down a substantial portion of the atmospheric CO2 solely through the solubility pump. In particular, 65-70% of all past emissions can be drawn down into the ocean. The longer it takes to reduce emissions, the less that the ocean solubility pump is able to draw down.

The new version of our model with an interactive solubility pump is now being used to examine the paleo questions listed in GR-201 (milestones 4 and 7).

Damon Matthews, an MSc student, has recently transferred to the PhD program. He has implemented a simple bucket land surface model into the UVic climate model (Milestone 2) and has used it to examine the effect of anthropogenic land surface changes on recent climate change (Matthews et al., 2002).

The effect of changing human land-use patterns on the climate of the past 300 years was discussed through analysis of a series of equilibrium and transient climate simulations using the new version of our model. Land-surface changes were prescribed through varying land cover type, representing the replacement of natural vegetation by human agricultural systems from 1700 to 1992. First, equilibrium climate simulations were conducted using (1) present-day vegetation, (2) year 1992 croplands superimposed onto a potential vegetation field and (3) year 1700 croplands superimposed onto potential vegetation. Second, a transient climate simulation forced by land-use changes alone was compared to a control and two other simulations, forced by: (1) changes in atmospheric CO2; and (2) changes in land-use and atmospheric CO2. All simulations showed a cooling resulting from land-use induced changes to surface albedo and evapotranspiration. The globally-averaged cooling was in the range of 0.09 to 0.22 °C, with larger regional changes caused by local positive feedbacks. Transient runs showed that land-use cooling is in the range of 12 to 22% of the magnitude of greenhouse gas induced warming.

Katrin Meissner, a postdoctoral fellow, has now implemented the Hadley Centre dynamic vegetation code TRIFFID into our model. She has also added an additional land surface scheme (a leaky bucket based on the Hadley Centre MOSES model) and is currently writing up these results with application to the last glacial maximum and the mid Holocene climates. She is also in the process of adding a terrestrial carbon cycle component to the model, and she will be working closely with Damon Matthews as Damon begins his PhD work.

Dr. Meissner’s work was presented in a talk entitled "Vegetation model and land surface scheme - 2 new components of the UVic Earth System Climate Model" at the Canadian Global Coupled Climate Carbon Model (CGC3CM), Second Science Meeting, Terrestrial Theme Workshop, Holiday Inn Yorkdale, Toronto, June 14 & 15, 2002. As noted in the original proposal, there will be close and constant collaboration/interaction with members of the CFCAS CGC3CM group.

4: Publications: 2002, in press and submitted

Attached is a list of 2002 publications as well as those are in press or recently submitted. All publications directly supported by CFAS are indicated with a bold number and a ‘*’. Only one of the CFCAS funded articles has already appeared (in Science) and a reprint is attached with this report. CFCAS funding is acknowledged in all papers that were supported by GR-201 research grant funds.

2002:

1. Weaver, A.J., M. Eby, E. C. Wiebe, C. M. Bitz, P. B. Duffy, T. L. Ewen, A. F. Fanning, M. M. Holland, A. MacFadyen, H. D. Matthews, K. J. Meissner, O. Saenko, A. Schmittner, H. Wang and M. Yoshimori, 2001: The UVic Earth System Climate Model: Model description, climatology and application to past, present and future climates. Atmosphere-Ocean, 39, 361—428.

2. Yoshimori, M., M.C. Reader, A.J. Weaver and N.A. MacFarlane, 2002: On the causes of glacial inception at 116KaBP. Climate Dynamics, 18, 383—402.

3. Clark, P.U., N.G. Pisias, T.F. Stocker, and A.J. Weaver, 2002: The role of the thermohaline circulation in abrupt climate change. Nature, 415, 863—869.

4*. Schmittner, A., M. Yoshimori and A.J. Weaver, 2002: Instability of glacial climate in a model of the ocean-atmosphere-cryosphere system. Science, 295, 1489—1493.

5. Claussen, M., L. A. Mysak, A. J. Weaver, M. Crucifix, T. Fichefet, M.-F. Loutre, S. L. Weber, J. Alcamo, V.A. Alexeev, A. Berger, R. Calov, A. Ganopolski, H. Goosse, G. Lohman, F. Lunkeit, I.I. Mohkov, V. Petoukhov, P. Stone and Z. Wang, 2001: Earth system models of intermediate complexity: Closing the gap in the spectrum of climate system models. Climate Dynamics, 18, 579—586.

6. Saenko, O., G. M. Flato and A. J. Weaver, 2002: Improved representation of sea-ice processes in climate models. Atmosphere-Ocean, 40, 21—43.

In press:

7. Schmittner, A., K.J. Meissner, M. Eby and A. J. Weaver, 2001: Forcing of the deep ocean circulation in simulations of the Last Glacial Maximum. Paleoceanography, in press.

8. Meissner, K.J., A. Schmittner, E.C. Wiebe and A.J. Weaver, 2002: Simulations of Heinrich Events in a coupled ocean-atmosphere-sea ice model. Geophysical Research Letters, in press.

9. McLaughlin, F.A., E. Carmack, R. Macdonald, A.J. Weaver and J. Smith, 2002: The Canada Basin 1989-1995: Upstream events and far-field effects of the Barents Sea branch. Journal of Geophysical Research., in press.

10. de Vernal, A., C. Hillaire-Marcel, W.R. Peltier and A.J. Weaver, 2002: The structure of the upper water column in the northwest North Atlantic: Modern vs. last glacial maximum conditions. Paleoceanography, in press.

11. Stone, D.A., and A. J. Weaver, 2002: Daily maximum and minimum temperature trends in a climate model. Geophysical Research Letters, in press.

12. Saenko, O.A., E.C. Wiebe, and A.J. Weaver, 2002: North Atlantic response to the above-normal export of sea-ice from the Arctic. J. Geophys. Res., in press.

13. Saenko, O.A., A. Schmittner, and A.J. Weaver, 2002: On the role of wind-driven sea ice motion on ocean ventilation. Journal of Physical Oceanography, in press.

Submitted

14. Arfeuille, G., A.J. Weaver, E.C. Carmack, F.A. McLaughlin, and G.M. Flato, 2002: Freshwater transport through the southwest Canadian Arctic Archipelago due to buoyancy and wind forcing: Dolphin and Union Strait to Queen Maud Gulf. Atmosphere-Ocean, submitted.

15. Weaver, A.J., 2002: The science of climate change. In: Climate Change in Canada. Coward, H.G., and A.J. Weaver, Eds. Wilfred Laurier Press, Waterloo, Ontario, Canada, submitted.

16. Saenko, O.A., J.M. Gregory, A.J. Weaver and M. Eby, 2002: Distinguishing the influences of heat, freshwater and momentum fluxes on ocean circulation and climate. Journal of Climate, submitted.

17. Stone, D.A. and A.J. Weaver, 2002: Diurnal temperature range trends in 20th and 21st century simulations of the CCCma coupled model. Climate Dynamics, submitted.

18*. Meissner, K.J., A. Schmittner and A.J. Weaver, 2002: The ventilation of the North Atlantic Ocean during the Last Glacial Maximum – A comparison between simulated and observed radiocarbon ages. Paleoceanography, submitted.

19. Hill, K.L., A.J. Weaver, H.J. Freeland and A. Bychkov, 2002: Evidence for change in the Sea of Okhotsk: Implications for the North Pacific. Atmosphere-Ocean, submitted.

20. Simmons, H.L., S.R. Jayne, L.C. St. Laurent and A.J. Weaver, 2002: Tidally driven mixing in the oceanic general circulation. Ocean Modelling, submitted.

21. Saenko, O.A., A.J. Weaver and M.H. England, 2002: A region of enhanced northward Antarctic intermediate Water transport in a coupled climate model. Journal of Physical Oceanography, submitted.

22*. Matthews, H.D., A.J. Weaver, M. Eby and K.J. Meissner, 2002: The effect of land-use change on 20th century climate as simulated by a climate model of intermediate complexity. Geophysical Research Letters, submitted.

23. Gillett, N.P., F.W. Zwiers, A.J. Weaver, G.C. Hegerl, M.R. Allen and P.A. Stott, 2002: Detecting anthropogenic influence with a multi model ensemble. Geophysical Research Letters, submitted.

24*. Ewen, T.L., A.J. Weaver and M. Eby, 2002: Response of the inorganic ocean carbon cycle to future warming in a coupled climate model. Global Biogeochemical Cycles, submitted.

25. Saenko, O.A., and A.J. Weaver, 2002: The effect of Southern Ocean upwelling on the global overturning streamfunction. Tellus, submitted.

26. National Research Council, 2002: Climate Change Feedbacks: Characterizing and Reducing Uncertainties, National Academy Press, 130pp, submitted.

27*. Schmittner, A., O.A. Saenko, and A.J. Weaver, 2002: Coupling of the hemispheres in observations and simulations of glacial climate change. Quaternary Science Reviews, submitted.