A new version of a global coupled atmosphere−ocean general circulation model(MRI−CGCM2)has been developed atthe Meteorological Research Institute(MRD．The model canbeusedto explore climate changeassociatedwithanthropogenicforcings．Weaimedtoreducethedrawbacksofthefomerversion ofthemodel(MRI−CGCM1，Tokiokaαα」．，1996)and achieve amore realisticclimaticmean andvariabili取 to predictclimate changeswith greater accuracy． In a preliminary analysis of the control run，the model showed generally goo(1performance in

Experiments related to twentieth century historical climate changes and the twenty-first century scenario are performed with the latest version of the MRI climate model, MRI-CGCM2.3. The model reproduces globally averaged surface air temperature (SAT) variations in the twentieth century with satisfactory agreement with interdecadal changes of the observed trend, as well as with the overall SAT increase of 0.5°C at the present-day compared to the pre-industrial level. The globally averaged SAT rises 2.4°C in the late twenty-first century in the experiment for scenario A1B of the Special Report on Emissions Scenarios (SRES) by the Intergovernmental Panel on Climate Change (IPCC). The spatial structures of the simulated trends for the late twentieth century are validated in various atmospheric fields through comparisons with observed data, which indicate that the model demonstrates reasonable agreement with the observed trend in each field. Most of the simulated changes for the twenty-first century reveal spatial patterns similar to those in the trends that appeared in the late twentieth century. The simulated trend patterns of the sea-level pressure (SLP) in both hemispheres bear a resemblance to the observed trends, with each spatial structure reminiscent of the annular modes in the northern and southern hemispheres (NAM and SAM). These SLP trend patterns are consistent with the trends in the SAT, precipitation, and zonal mean zonal wind fields, as in the NAM and SAM. The coherent trend structures of these fields are projected to be enhanced in twenty-first century climate changes. Changes of ocean and sea-ice in association with these atmospheric changes are also described.

We have developed a general-purpose simple coupler (Scup) that can be used for earth system modeling. Scup allows flexible coupling among component models, for example, atmosphere and ocean general circulation models and chemical transport models. Although Scup has provided functions that are required for the efficient development of an earth system model at the Meteorological Research Institute, its fundamental design should also be applicable to other earth system models. Processes of the component models communicate with each other directly by calling the Scup library, which is necessary to efficiently exchange large amounts of grid data among the processes of the component models. Scup supports grid transformation for three-dimensional data and that for two-dimensional data with accurate local and global conservation, necessary features for coupling component models with different coordinates or grids.Simplicity and ease of use are among Scup's strong points. All of the source code is written in Fortran and can be compiled on various platforms with a Fortran 95 compiler and a Message Passing Interface library, so it has good portability.