Abstract: In order to investigate possible climate change over the western North Pacific (WNP) under global warming scenario, which is the background for the projection of future typhoon activities, outputs of 18 GCMs from the CMIP3 multimodel dataset are emplo yed. The background fields considered in this paper include the sea surface temperature (SST), the magnitude of vertical zonal wind shear (MWS), the sea level pressure (SLP), the outgoing longwave radiation (OLR) and the precipitation. These fields are all closely related to typhoon activities. We compare the changes of these fields during typhoon season (June to October) between SRES A2 experiment and 20C3M experiment for the two periods of 2080-2099 and 1980-1999. The analyses of the change in the multimodel ensemble (MME) and the consistency among the models are mainly presented in this paper. The results show that there is a warming in SST over the entire WNP area with increment larger than 2 ℃. And all the 18 models show the same tendency. The signal to noise ratio for SST is larger than 4 over most of the area. The precipitation in the MME also increases over the entire WNP area with larger change over the lower latitudes. More than 12 models show more precipitation over most of the WNP area, where the signal to noise ratio is mostly larger than 0.6. For the projection of SLP, both of the high and low pressure systems become weaker in SRES A2 and the change in low pressure area is more robust among the models with signal to noise ratio mainly larger than 0.6. There are no consistent changes in the MWS and the OLR over the entire WNP. And the spread of projection in the different models is larger than that in the other variables. The signal to noise ratio for both the MWS and the OLR is about 0.3 for most of the WNP area. But over the key areas where there are significant negative correlations between the MWS, the OLR and the typhoon frequency in the observations, the area averaged MWS and OLR in the MME decrease in SRES A2, and most of the 18 model shows the same tendency. Changes in the SST, precipitation, MWS and OLR over the key areas could imply that the background fields become favorable to typhoon activities in global warming secnario. But nowadays, the mechanism of the influence of large scale environmental factors on the tropical cyclone behaviours still remains to be fully understood, so it is needed to further analyse how exactly the typhoon activities react to the change in background fields.