What was done
The authors analyzed trends and oscillations in monthly and annual frequencies of tropical cyclones in the North Indian Ocean from 1877 to 1998, over which time the earth warmed significantly as it recovered from the global chill of the Little Ice Age.

What was learned
The analysis produced a mixed bag of results, with some months exhibiting an increase in tropical cyclone frequency, some months a decrease, and some months no trend at all.  Considered annually, tropical cyclone frequency in the North Indian Ocean experienced a slightly decreasing, but non-significant, trend of -0.8/100 years.

Spectral analyses of the monthly and annual data revealed several cycles of various periodicities, the most pronounced of which were 2-5, 10, 13 and 29 years.  Further analyses, using monthly tropical cyclone data from the Bay of Bengal (located within the authors' North Indian Ocean study area) and the Southern Oscillation Index, revealed that tropical cyclone frequency declined during the months of most severe cyclone formation - November and May - when ENSO was in a warm phase.

What it means
This study, as is also the case with many others (see the Hurricanes section of our Subject Index), refutes the climate alarmist claim that global warming will result in more frequent and more intense major storms, as evidenced by the decline in the frequency of severe tropical cyclones in the North Indian Ocean during warmer El Niņo years and by the overall small decline in annual cyclone numbers over a period of demonstrable global warming.