Abstract: Using the forecasts of the five general circulation models distributed by the IPCC, the large-scale environment over the western North Pacific (WNP) under the high (SRES A2) and low (SRES B1) emission scenarios in the 21st century are projected. The results show that the 500 hPa geopotential height over the tropical WNP and the sea surface temperature, especially in the east-central tropic Pacific, both will be above normal. Furthermore, the low-level anomalous anti-cyclonic circulation will cover the region east to the Philippines in the 21st century. Thus the large-scale environment will not be conducive to the formation of tropical cyclones (TCs), and such an environment will be more remarkable under the SRES A2 scenario or after the mid-21st century. The frequency of TC will possibly decline, but the decreasing trend under the SRES B1 scenario will be weaker than that under the SRES A2. There will still be interdecadal and interannual fluctuations of TC frequency in the 21st century.

Key words: tropical cyclone, trend, scenario, projection