| Consistent increase of anthropogenic greenhouse gas (GHG) emission has led to global climate change since 20th century. Lots of research about the impact of GHG on global ocean and atmosphere are carried on. In earlier research, the linear trend of variables was commonly used to represent the effect of GHG. In this study, however, it is found that the linear trend method is not fit for the North Pacific (NP) research, for there is decadal-scale variability in NP (as known as PDO) and the linear trend will be interfered by the phase shift of the variability. The impact of GHG on climate is accumulative, which can surpass that of natural variability when the growth rate and the concentration is up to a higher level. A new method is raised in this study that can reasonably estimate the impact of GHG in NP. Based on IPCC AR4 models project in Special Report on Emissions Scenarios (SRES) A1B, a formula is put forward to calculate the influence of GHG. The new method is used to estimate the response of the NP oceanic and atmospheric circulation to increasing GHG. Some new features have been found as follows:1. As response to GHG increase, the NP Sea Surface Temperature (SST) increases all over the basin, 0.33℃on average, less than 0.4℃in low-latitude, higher than 0.6℃in high-latitude and polar region. The latent heat flux increases by 0.22W/㎡(upward positive). The contribution of surface relative humidity, sea-air temperature difference and wind speed are -1.7 W/㎡, -2 W/㎡ and 3.92 W/㎡. The sensible heat flux is reduced by 0.4 W/㎡, mostly due to the less sea-air temperature difference. The shortwave radiation reaching the surface decreases by 0.33 W/㎡, while the net downwelling longwave radiation increases by 0.53 W/㎡. As a result, the net heat flux change was -0.37 W/㎡, suggesting that ocean gets more heat from atmosphere as response to GHG increase. The SST increases by about 0.3℃and the net heat flux by about 3 W/㎡ near the Kuroshio and Kuroshio Extent region. 2. The geopotential height root mean square (rms) at 500hPa layer over NP in boreal winter decreased by about 1gpm, denoting the weakening of NP storm track. A possible reason is the decrease of atmospheric baroclinity, as shown by the decrease of Eady growth rate by about -0.12 s-1. The Aleutian Low in boreal winter is also weakened by about 3gpm at 1000hPa layer. It suggests the strengthening phenomenon of NP storm track and Aleutian Low found in earlier research was mostly the feature of PDO phase shift.3. The zonal-mean Hadley circulation is widened in both hemispheres caused by GHG increase, but less than 0.2°in all, while the intensity of the circulation is weakened by about 0.9%. Comparing the earlier results, it indicates the poleward expansion of Hadley Circulation by about 2°during the recent 25 years was probably attributed to decadal-scale natural variability, rather than the GHG increase.Conclusions above could be as a reference to the future research on impact of increasing GHG. It will be helpful to the long term climate prediction.
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