The coupled model intercomparison project (CMIP)
Gerald A. Meehl
National Center for Atmospheric Research, Boulder, Colorado
George J. Boer
Canadian Centre for Modeling and Analysis, Canada
Curt Covey
Program for Climate Model Diagnostics and Intercomparison, U.S.A.
Mojib Latif
Max Planck Institute for Meteorology, Germany
Ronald J. Stouffer
Geophysical Fluid Dynamics Laboratory, U.S.A.
CMIP is a project to study and intercompare climate simulations made with
coupled ocean/atmosphere/cryosphere/land GCMs. There are two main phases (CMIP1
and CMIP2) which study: (1) the ability of models to simulate the present-day
climate, and (2) model simulation of climate change due to an idealized change
in forcing (a 1% per year CO2 increase). CMIP was initiated in
December 1995 as part of the overall modelling activities within the World
Climate Research Programme (WCRP). Since that time, present-day climate
simulations from 19 models (CMIP1), and forced climate change results from 12 of
these models (CMIP2) have been archived by the US Department of Energy Programme
for Climate Model Diagnosis and Intercomparison (PCMDI). Virtually all global
coupled modeling efforts in the world are represented in this data set held by
PCMDI. The model results are available for analysis via "diagnostic subprojects"
which concentrate on a particular aspect of climate and model behavior (and
which attempt to entrain expertise outside of the modelling community in this
analysis). There are currently 10 CMIP1 subprojects analyzing aspects of
present-day climate simulations and 9 CMIP2 subprojects analyzing the
CO2 increase experiments. Results from a number of subprojects were
reported at the 1st CMIP Workshop held in Melbourne. Australia at the Bureau of
Meteorology Research Centre from 14-15 October, 1998. Some recent advances in
global coupled modeling related to CMIP were also reported. Presentations were
based on preliminary (sometimes controversial) unpublished results. reflecting
the personal views of the participants. Some of the results from the workshop
are: 1) most observed processes are simulated in the global coupled models with
varying degrees of fidelity, including the North Atlantic Oscillation and
linkages to North Atlantic SSTs, the Antarctic Circumpolar Wave, El Nino-like
events, monsoon interannual variability, etc.; 2) the amplitude of both high and
low frequency surface temperature variability in some global coupled models is
less than that observed, which may be partly due to omission of low frequency
forcing agents in the models (e.g. solar, volcanos, etc.), and this has
implications for climate change detection/attribution studies that rely on model
results for estimates of natural low frequency variability; 3) in the
CO2 climate change experiments, an El Nino-like pattern in the mean
SST response such that there is greater mean surface warming in the eastern
equatorial Pacific than the westren equatorial Pacific is simulated by a number
of models but other models have little, or even a La Nina-like response; this
complicates a simple understanding of climate change anomalies in the Pacific
region; 4) though flux adjustment improves the simulation of present-day climate
and produces a stable base state to enable very long term (1000 years and
longer) integrations, it does not appear to have a major effect on model
processes or model response to increasing CO2; and 5) recent
multicentury integrations that produce a stable surface climate without flux
adjustment (though still with some systematic simulation errors) signify a
substantial increase in our understanding of the causes of climate drift and the
need for flux adjustments. This has led to improvements in the model components
and the initialization procedures used in these models.
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Hongjun Zhang:
zhangho@ucar.edu