With the one-year anniversary of hurricane Katrina fast
approaching, I want to share some findings reported by Bjorn Lomborg in his
2001 book The Skeptical Environmentalist  (pages 294-295).
The observed evidence counts against the idea of increased
frequency of tropical cyclones. Generally,
it has been impossible to establish a reliable global record of variability of
tropical cyclones through the twentieth century because of changing observing
systems and population changes in tropical areas. Based on relatively short time series, the
Northwest Pacific basin has shown an increase in tropical cyclones since 1980,
preceded by an almost identical decrease in frequency from about 1960 to 1980. Since the 1960s, the Northeast Pacific has
experienced a significant upward trend in tropical cyclone frequency, the North
Indian Ocean a significant downward trend, and not appreciable long-term
variation was observed in the Southwest Indian Ocean and Southwest Pacific. Finally, the
numbers of tropical cyclones occurring in the Australian region have decreased
since the mid-1980s.
However, the North Atlantic has good cyclone data because weather aircraft have reconnoitered there since
the 1940s. Here, it turns out that
although there are great decadal variations, the trends are generally
declining, with a noticeable quiet period in the 1970s and 1980s. Particularly, it turns out that the number of
intense cyclones (those that cause the greatest damage) has been declining, as
has the number of cyclone days. Equally,
and as shown in Figure 152 [unavailable on line], the average [maximum sustained] wind [speed] of an
Atlantic cyclone has been decreasing over the past half-century.
These data, of course, are pre-Katrina (which was a category
three storm when it made landfall on August 29, 2005, just east of New Orleans – and which, despite being a major
tragedy, doesn’t come close  to being a killer of the magnitude of the hurricane that hit Galveston, Texas, in 1900).