Marine Ecosystems Research Department - jamstec japan agency ...

Japan Marine Science and Technology Center
Frontier Research System for Global Change
c. Development of a Cryospheric Climate System Model
Ice sheets are huge glaciers that extend over the continents.
At present there are two ice sheets on the earth,
the Antarctic ice sheet and the Greenland ice sheet,
which are together equivalent to more than meters'
sea level. Slight changes in the ice sheets have the potential
to affect the geography and economy of the world's
coastal regions. Therefore it is critical that we understand
how much the ice sheets will change in size due to
future changes, such as Global Warming. The aim of our
research is to tackle these issues by using coupled models
of the ice sheets, the atmosphere and the seaiceoceans
to simulate the evolution of the ice sheets. Runs
on the Earth Simulator supercomputer are planned.
For FY, the ice sheet model was developed and
validated, since it has to sufficiently simulate the present
situation. Sensitivity of the ice sheet model to
regional warming was investigated and it was found
that a to degree Celsius warming is sufficient for
the Greenland ice sheet to fall to half its volume or
raise the sea level by meters, although the response
time is in the order of hundreds to thousands of years.
For the future prediction, not only the ice sheet model
but also the climate model (General Circulation Model,
GCM) should predict the regional climate changes
over the Antarctic and Greenland ice sheet region with
both high resolution and high precision, since ice sheet
is very sensitive to small temperature changes. The
evaluation of the atmospheric GCM is done in a high
resolution (T, deg. lat. and lon.) AGCM, which
was done so far only by one GCM (ECHAM) referred
in the IPCC Third Assessment Report. It is concluded
that careful treatment of the albedo of the snow over
the ice sheet and the altitude correction could bring
about a more realistic result. Moreover, one way coupling
of high resolution GCM to Ice sheet model was
attempted. The role of ice sheet flow becomes important
after the st century and lasts for a millennium.
Since this one-way coupling does not include the
detailed scenario of warming and the albedo feedback
effect, the fully coupled ice sheet – GCM is essential
for the next step.
To investigate the other important cryosphere component,
sea ice, in the coupled GCM, we focused on
sea ice dynamics and assessed its effect on the presentday
sea ice climatology. Previous studies using numerical
models have shown that summer sea ice area in the
Southern Ocean decreases due to the sea ice dynamics.
In winter, on the other hand, sea ice dynamics cause
little difference in the simulated sea ice area. However,
one of the reasons for this less sensitivity in winter
may be that the dynamic response of the ocean, such as
convection, has not been incorporated in the sea ice
models used in the experiments. In the present study,
therefore, we employ a coupled ocean-atmosphere
GCM (OAGCM) to verify whether sea ice dynamics
can affect sea ice distribution by controlling the ocean
convection process. It is found that (a) sea ice dynamics
increase the static stability of the ocean by enhancing
freshwater release near the ice edge, and (b) sea ice
dynamics increase the static stability by decreasing the
sea ice concentration and thickness, which enhances
the deep water cooling in winter (especially near the
Antarctic continent). In the Northern Hemisphere, on
the other hand, impact of sea ice dynamics on the sea
ice extent appears to be minor, although significant
effect on sea ice thickness was found.
d. Improvement of the Physical Climate System Model
The main objective of this sub-group is to improve a
climate model (CCSR/NIES model) which consists of
a coupled atmosphere and ocean general circulation
model (GCM), a sea ice model, and a land surface
model. In particular, various important processes in the
stratosphere will be improved and/or newly implemented.
The effects of anthropogenic gases and aerosols on
the ozone chemistry may cause dramatic climate variability
over the whole atmosphere through complex
interactions between radiative and dynamical processes.
In addition, variability of solar radiation can cause
ozone changes and climate variability in the middle
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