Background
The authors write that "the tropical cyclone (TC) is one of the most destructive natural disasters that cause loss of lives and enormous property damages around the world," adding that "the western North Pacific (WNP) is an area where typhoon activity is the most frequent and strongest and China is one of the countries that seriously suffered from typhoons in this area."

What was done
Using the latest TC data -- "those in the yearbooks of TC of the WNP from 1960 to 2005" -- Lu et al. analyzed the interdecadal variation of WNP TCs and the large-scale circulation factors affecting them.

What was learned
The figure below illustrates the temporal variation of WNP TC frequency derived by the four scientists, who note that "the time period from 1960 to 2005 has two high frequency periods (HFP) and two low frequency periods (LFP)." They further note, in this regard, that "in HFP, the conditions include higher sea surface temperature, lower sea level pressure, larger divergence of upper air, larger relative vorticity of low level and smaller vertical shear," while "it is otherwise true with the LFP."

Tropical cyclone frequency vs. year. Blue line represent five-year running means, while the red line is a fifth-order polynomial that has been fit to the data points. Adapted from Lu et al. (2008).

What it means
Although relatively higher sea surface temperatures lead to relatively more WNP TCs in terms of the periodicity evident in the authors' data, it is clear that the longer-term global warming experienced by the earth has been accompanied by a longer-term decline in WNP TC frequency. Would this thus be a positive consequence of global warming???