NSERC CSHD Collaborative Special Project
Paleoclimatic Modelling using Coupled Ocean-Ice-Atmosphere Models (April 17, 1996)
The motivation and background for the Climate System History and
Paleoclimate proposal has been given in the Science Plan. Here we focus
on our component of this collaborative project.
Recently Augustus Fanning, a PhD student working under A. Weaver's
supervision, developed a diffusive heat transport energy balance model
that has been tested in both simplified and global domains. The EBM is
based upon the models of Budyko (1969), Sellers (1969), and North (1975).
have extended these models to allow coupling with the GFDL ocean general
circulation model (OGCM -- Pacanowski et al., 1993) by allowing latent,
sensible and radiative heat transfers between the ocean and atmosphere.
effort to completely couple the ocean-atmosphere system, a moisture
equation has also been added to the EBM so that freshwater fluxes can be
predicted for the ocean model.
The resultant EMBM has been run in a global 2deg. x 2deg. domain with
sea surface temperatures (Fanning and Weaver, 1996). Under climatological
oceanic conditions, the surface air temperatures, specific humidities and
surface fluxes are comparable to direct estimates. As an extension to the
climatological forcing case, a simple perturbation experiment was
which the 1955-59 pentad was compared to the 1970-74 pentad by driving
model under the respective sea surface temperatures. The model exhibits
as well as basin-mean temperature changes in the latter pentad comparable
direct estimates (Jones, 1988). These validations of the EMBM against the
present climate give us greater confidence in its ability to be applied
A global ocean general circulation model (OGCM) has also recently been
developed in collaboration with Warren Lee and others for coupling to the
Canadian Centre for Climate Modelling and Analysis (CCCMA) atmospheric
circulation model (AGCM). Two versions of this OGCM now exist: the first
high resolution model (1.8deg. x 1.8deg. x 29 levels) which has now been
coupled to the CCC AGCM to investigate the climatic response to
atmospheric greenhouse gases and aerosols. The second version of the
at slightly coarser resolution (3.6deg. x 1.8deg. x 19 levels). It is
latter, computationally-efficient, OGCM that we propose to use in this
a description of which may be found in Weaver and Hughes (1996).
Fanning and Weaver (1996) also show how the coupling of this EMBM and
into which a thermodynamic ice model (TIM) has been incorporated, leads
very reasonable simulation of the present climate. The virtue of this
atmospheric model is that we do not need to employ flux adjustments to
simulation of the present climate stable. Thus, it is relatively easy to
this model to past climates through a change in the seasonality and
of incoming solar radiation and through other changes in radiative
have also recently incorporated a simple parameterization which allows
wind-stress feedbacks through the calculation of geostrophic wind
where Rayleigh friction becomes important near the Equator. This coupled
is one of the numerical tools which we shall apply to the projects
This project will also include some aspects of the modelling work
within CSHD 5. [The latter project will be terminated as a result of Dr.
leaving Dalhousie University. Only aspects of CSHD 5 which we intend to
continue within the present project will be discussed here.] Within CSHD
low order climate model of Wright and Stocker has been extended to
representation of the major land masses as well as seasonal cycles
with variations in incoming shortwave radiation. These developments are
essential prerequisites for the inclusion of an active cryosphere
the model. An inorganic carbon cycle component of the model has also been
developed in collaboration Thomas Stocker of the Climate Research
the University of Bern. This work represents a step towards allowing for
influence of variations in atmospheric CO2 associated with exchanges
the ocean and the atmosphere. Both of these developments are relevant to
examination of climatic variations on the millenial timescale which
the second major focus of this project.
2. Simulation of the Younger Dryas event and the Transition from the
Last Glacial Maximum to the Holocene
The use of models to simulate past climatic events is an important
investigation if one is to have confidence in their application to future
climatic changes. To this end the realistic geometry, global, coupled
OGCM-EMBM-TIM (mentioned above) will be used to simulate the transition
the last glacial maximum and the present Holocene. During the transition,
abrupt return to glacial climatic conditions, known as the Younger Dryas
occurred. The YD cold episode was particularly pronounced in regions
the North Atlantic, and is evidenced in northern European and maritime
lakes and bogs; North Atlantic marine sediments; and northwestern
central Canadian glacial moraines. Although strongest in the northern
region, further evidence indicates the impacts of the YD were felt
While the exact cause of the YD is still unknown, a general consensus
emerged that it was linked to oceanographic phenomena. The amplification
YD signal in the northeastern North Atlantic suggests a primary role for
thermohaline circulation, particularly North Atlantic Deep Water (NADW)
production. The question naturally arises as to what source could supply
necessary excess freshwater needed to reduce NADW formation. The obvious
sources are the polar ice caps and the Laurentide and Fennoscandian ice
(LIS and FIS, respectively). The traditional viewpoint is that the YD was
triggered by the diversion of meltwater (due to the retreating LIS) from
Gulf of Mexico to the St. Lawrence (Broecker et al., 1988). However, the
that deep water is usually formed in local high-latitude regions of small
extent suggests that not only the amount, but also the location of
introduced is crucial for interrupting the North Atlantic Conveyor.
of changes in ocean circulation during the Younger Dryas event have
been done within CSHD 5 and 8, but the idealized models used in these
do not permit examination of the influence of meltwater input location.
study is thus a natural next step to be taken within the CSHD project.
We shall conduct experiments to reinvestigate the climatic implications
geographical and temporal change in the runoff from the LIS and FIS,
estimated meltwater and precipitation runoff from drainage basins in and
the North Atlantic, before, during, and after the YD (Teller, 1990).
Maier-Reimer and Mikolajewicz (1989), using an ocean-only model, found
were capable of shutting down NADW production within 200 years from the
they deflected 347 km3/yr from the Gulf of Mexico into the St.
Lawrence valley (roughly half that estimated to have occurred), our
results suggest the traditional meltwater diversion theory is incapable
inducing a shutdown of NADW in our EMBM. If, however, we apply the runoff
estimates previous to the YD, the conveyor is pushed to the brink,
diversion of LIS waters to completely halt NADW production. In an
experiment we will consider the role of the FIS meltwater on the YD
3. The Effect of Oceanic Gateways on Paleoclimate
As an extension of the above paleoclimatic experiment, we will also
sequence of experiments with the coupled model to investigate the
of opening and closing oceanic gateways such as the Isthmus of Panama and
Passage (about 3.5 and 30 million years ago, respectively). In
attention will be focused on the changes in meridional oceanic heat
and the relation to glacial events in the paleoclimate record.
4. The Dependence of Paleoclimate Variability on the Mean Climatic
Late last year we acquired the GFDL coupled climate model for use on A.
Weaver's local work station cluster. Drs. S. Valcke, S. Zhang and A.
now have this model running and are using it (in close collaboration with
Stouffer and Suki Manabe) to investigate the existence of climate
in the coupled climate system and how it varies as the mean climatic
changes. We plan to initially use the coupled EMBM-TIM-OGCM to streamline
experiments that we will perform with the GFDL coupled model as it is
and hence more computationally efficient.
We intend to examine the hypotheses of Weaver and Hughes (1994) and Tang
Weaver (1995) that warmer climates may be more variable due to an
intensification of the hydrological cycle. In addition, we will
whether colder climates are also more unstable through ice-thermohaline
circulation instabilities (Broecker et al., 1990) or through
diffusive-timescale internal oceanic oscillations (Weaver and Sarachik,
That is, we wish to understand why the Holocene has exhibited a
stable climate which appears to be unparalleled in recent Earth's
5. Confirmation of Dansgaard-Oeschger oscillations in low-order
Considering the potential significance of the discovery of
Dansgaard-Oeschger-like oscillations in the model of Sakai and Peltier
it is appropriate to determine if similar variability may exist in the
viscid model of Wright and Stocker. If similar variability is found, it
of interest to determine if the same physical mechanism is responsible
variability in the two models. As part of this investigation, a
of the Wright and Stocker code to explicitely include vertical and
diffusion of momentum is being developed. Analysis of model runs will
clarify the strengths and weaknesses of both modelling approaches and
subsequent work will be carried out with an appropriately generalized
formulation. It should also be noted that the earlier work of Tang and
(1995) is directly relevant to this topic and comparisons with their
will also be investigated.
6. Improved representations of land-sea and seasonal variations in the
extended Wright and Stocker climate model
In order to extend a low order climate model to include an active
it must include both realistic seasonal variations and land-sea contrast.
low order climate model of Wright and Stocker has been extended to
these effects within the CSHD 5 project. However, comparison with the
Crutcher-Meserve and GEDEX data sets reveals significant discrepancies in
aspects of the model's variability, suggesting inadequacies in the
component of the model. Indeed, it appears likely that the atmosphere is
weakest component of the Wright and Stocker climate model and improvement
highly desirable. As part of the present project, we will perform
diagnostic analysis of model results to determine the major source(s) of
discrepancies; implement appropriate improvements in the atmospheric
hydrological cycle, and coupling procedure; and verify results against
7. Investigation of the influence of variations in the thermohaline
circulation on ice sheet growth and decay
Once the atmospheric component of the climate model has been improved
verified, we will implement an idealized cryosphere component into the
We will survey the literature to identify an existing model of the
which is consistent with our overall goal of developing a highly
dynamically consistent model of the global climate system. The modelling
approach followed by Weertman (1961, 1976), Pollard (1978) and Oerlemans
co-workers (1980, 1982, 1984) are generally consistent with ours and
more recent adaptations will be considered. After an appropriate model is
identified, implemented, tested and (presumably) modified we will examine
oceanic influence on ice sheet variations. The final aspect of this
will be the incorporation of a carbon cycle component in the model which
allow for the exchange of carbon between the oceanic and atmospheric
reservoirs. Initially, our intention is simply to determine the magnitude
the changes induced by including atmospheric carbon dioxide variations in
model which includes the feedbacks associated with both the oceans and
8. References not in the NSERC Personal Data Forms 100
Broecker, W.S. et al., 1988: The chronology of the last deglaciation:
Implications to the cause of the Younger Dryas event.
Broecker, W.S. et al., 1990: A salt oscillator in the glacial
Atlantic? -- The concept. Paleoceanogr., 5, 469-477.
Budyko, M.I., 1969: The effect of solar radiation variations on
climate of the earth. Tellus, 21, 611-619.
Jones, P.D., 1988: Hemispheric surface air temperature variations:
Recent trends and an update to 1987. J. Climate, 1,
Maier-Reimer, E. and U. Mikolajewicz, 1989: Experiments with an
OGCM on the cause of the Younger Dryas, Max Planck Institute fur Meteorologie,
#39, 13 pp.
North, G.R., 1975: Theory of energy balance climate models. J.
Sci., 32, 2033-2043.
Oerlemans, J., 1980: Model experiments on the 100,000 yr glacial
Nature, 287, 430-432.
Oerlemans, J., 1982: Glacial cycles and ice-sheet modelling.
Change, 4, 353-374.
Oerlemans, J. and C.J. van der Veen, 1984: Ice Sheets and
Climate, 217pp., Riedel.
Pacanowski, R. et al., 1993: The GFDL Modular Ocean Model Users
GFDL Ocean Group Technical Report #2, 46pp.
Pollard, D., 1978: An investigation of the astronomical theory of
the ice ages using a simple climate-ice sheet model. Nature,
Sakai, K. and W.R. Peltier, 1995: A Simple Model of the Atlantic
Thermohaline Circulation: Inernal and Forced Variability with
Paleoclimatological Implications, J. Geophys. Res., 100,
Sellers, W.D., 1969: A global climatic model based on the energy
of the earth-atmosphere system. J. Appl. Meteorol., 8,
Teller, J.T., 1990: Meltwater and precipitation runoff to the
North Atlantic, Arctic, and Gulf of Mexico from the Laurentide Ice sheet and
adjacent regions during the Younger Dryas, Paleoceanogr., 5,
Justification for Budget Request:
1) Salaries and benefits
a) Graduate Students
Full support for one student (P. Poussart who arrives in September 1996;
partial support for A. Fanning and T. Murdock until September, 1996) at
current NSERC rate. This project will involve 3 graduate students
Murdock, Poussart). Fanning and Murdock should graduate early into the
this project. I suspect Murdock will continue on in the PhD program once
receives his MSc. Murdock will be partially supported off my NOAA Grant
Fanning is partially supported by an Atlantic Career Development
d) Postdoctoral Fellows/Research Associates
Full support for S. Zhang (UVic) and D. Brickman (Dal) for 1996-1997
1997-1998. Full support for Dr. Sophie Valcke from year 2 onwards. She is
currently completing the first year of her NSERC Post doctoral
3) Materials and Supplies
Toner cartridges, computer paper, magnetic tapes, computer manuals,
costs, video cassettes for computer movies, photocopying charges,
charges (telephone, fax, courier) etc.
Travel to CHSD annual meetings.
5) Dissemination Costs
Publication and reprint charges. The total ($8,000) is significantly less
we have had to pay out during the 1995-96 fiscal year (~$25,000).
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