It has been recently recognized in the field of earth science that the earth's surface environment around us is a system formed through interactions between its components such as atmosphere, ocean, land, and biota. So far, these components have been subjects of separate disciplines. Recently, however, it is becoming more and more important to recognize processes forming the global environment with a well-balanced set of necessary perceptions obtained in different disciplines. 10th session of the Conference of the Parties (COP10), which took place in December 2004 in Buenos Aires, Argentina, provides a good example. The high government officials from all over the world discussed implementation of the Kyoto Protocol that imposes a duty on advanced countries to reduce CO2 emission. Here, the effect of the implementation will remain unknown unless we synthesize various kinds of knowledge from many different fields to answer questions such as: to what extent can forests and oceans uptake anthropogenic CO2? (Ecology, Oceanography); given a certain amount of increase in CO2 concentration, what would be the corresponding temperature rise? (Meteorology); and, will green houses gasses other than CO2 increase in the future? (Atmospheric chemistry). Furthermore, the issue of feedback processes is needed to be examined, as the one between temperature rise and the carbon cycle in both terrestrial and marine ecosystems, may complicate the projection of CO2 concentration. In order to comprehensively simulate the earth system, numerical models used for global environment projection have to be extended. They have to include various processes related to the above questions as realistically as possible. Realizing such circumstances, FRCGC launched a project to develop an integrated earth system model as category 2 of Research Project for Sustainable Coexistence of Human, Nature, and the Earth funded by Ministry of Education, Culture, Sports, Science and Technology (MEXT) (shortly called Kyousei Project after its Japanese name). FRCGC has six research programs that cover most fields relevant to global environmental changes, and the programs have been developing models dedicated to their own disciplines. FRCGC is thus well-equipped for constructing an "integrated earth system model" by combining those component models of global change (Fig.1). As of January 2005, all the component models except for vegetation dynamics have been coupled on the code, although further fine tuning is necessary in order to perform realistic simulations. We have recently obtained some preliminary results regarding carbon cycle modeling. Following are the outputs of our recent experiments.