JunkScience.com
September 4, 2004
It's Hurricane Season and the claims are escalating faster than the storms. Already we've had Knight Ridder Newspapers claiming "The past nine years, from 1995 through 2003, mark the busiest, most intense nine-year storm period on record" based, apparently, on this Climate Prediction Center graphic. Of course, if you choose your "record" carefully enough you can prove anything - but it is not necessarily instructive to do so.
The National Hurricane Center provides a somewhat longer perspective online in U.S. Hurricane Strikes by Decade. From that table it is a simple matter to create a pretty graphic. The thumbnail at right links to a stacked column graph of U.S. landfalling hurricanes by Saffir-Simpson Category and decade. Counts are not labeled for category 5 storms, one occurring in each of the 30s, 60s and 90s (with Hurricane Andrew [1992] having been escalated from cat 4 to cat 5 on reanalysis in 2002).
On a raw count it appears the 1940s were pretty active while the 1970s were rather quiet. Naturally this doesn't necessarily mean that the ferocity of these storms are comparable so we need to differentiate by some sort of composite rating.
A quick check on the numbers of more severe storms (cat 3-5), already tallied for us on the linked NHC page, indicates a similar high/low pattern but it would be nice to have something better than simple raw counts. How about using the storms' Saffir-Simpson Category as a point system? This will give us an instant weighting system so we can accumulate both the number and severity of storms in any given decade - think of it as a sort of decadal hurricane ferocity score.
Perhaps an activity rating would be the more accurate description because the second half of the Twentieth Century does not appear as ferocious as the first.
Granted, this is a very rudimentary analysis but it does suffice to demonstrate the effect of record selection. It is entirely possible, in fact probable, that the Climate Prediction Center has only that length of record with sufficient data to perform their total energy analysis but it does not justify Knight Ridder's claim of "busiest, most intense" period on record.
According to The Most Intense Hurricanes in the United States 1900-2000 only 28 of the listed 65 events occurred since 1950. The Deadliest, Costliest, And Most Intense United States Hurricanes From 1900 To 2000 (And Other Frequently Requested Hurricane Facts) indicates that fully half the years when no hurricanes struck mainland U.S. are after 1950 (10 of 19). The most hurricanes to strike in one year were six in 1916 and 1985. There were five in 1933, and four in 1906, 1909, and 1964. Three hurricanes struck the U.S. in one year a total of sixteen times. Ten of these sixteen times occurred during the sixteen years from 1944 to 1959.
It would appear our rough and ready activity rating scheme of allocating and accruing points by Saffir-Simpson Category adequately reflects the relative severity of the hurricane cycle. While not fully represent the energy of the season a total event count obviously gives a rough approximation of the season severity.
The one thing we did not find is any suggestion of increasing hurricane season severity. The most active period within the Twentieth Century record is the 1930s-1960s with something of a lull subsequently. This is not supportive of the hypothesis that the globe is warming catastrophically or that there are more and more severe storms occurring.
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