TCS Daily

Is the Current Era of Hurricane Activity Unprecedented?

By Anthony Lupo - September 30, 2005 12:00 AM

In the age of instant media, the pictures coming from the southeastern United States of the damage wrought by the one-two punch of Hurricanes Katrina and Rita have triggered a generous response from our nation to those hurt the most by these storms. But even as Katrina  was cutting a swath of destruction across the southeast part of our country, there were those who were content to wag their finger and put the blame for all the devastation squarely on the shoulders of us all by saying that Katrina (1), and then Rita, were products of man-made global warming.

Aside from the fallacy of attributing the intensity of one or two storms to climate change, regardless of the cause of the change, there are other reasons not to jump to the conclusion that hurricanes like Katrina somehow are a sure sign of global warming and, more importantly, of things to come. While these storms were intense -- their central pressures bottoming out as two of the most powerful ever to occur in the Atlantic Ocean basin -- storms of this magnitude have not occurred since Mitch in 1998. Including Katrina and Rita, only six such storms have occurred since 1969, and only one other of these storms struck the United States while it was still a category 5 event.


Are two storms as severe as Katrina and Rita in the same year in the Atlantic Ocean basin unprecedented? No, Carla and Hattie were category five storms in 1961. The year before that, 1960, Donna and Ethel were both category five storms which occurred within a three week period at the end of August to mid-September, and both of these storms hit the United States. 


It can be argued that the hurricane activity in recent times -- for example 33 hurricanes occurring in the Atlantic from 1995-1998 -- has been unprecedented (1) and may be attributable to climate change. A new paper, by Webster et al. (2), published recently made the case that the number of intense hurricanes worldwide has increased nearly 80% since 1970. Aside from the fact that the study covers a relatively short period and begins close to a long-term period of reduced hurricane activity (3,4), the study is used as evidence that global warming has caused an alarming increase in hurricane activity. Looking in the Atlantic Ocean basin alone, since it has the longest available reliable record, reveals that the number of hurricanes from 2000 - 2005 has seen 46 storms, including 15 intense storms (category 4 and 5).


However, one of the worlds foremost experts on hurricanes (5), has been saying for years that the recent increase in hurricane activity in the Atlantic is due to the complex interplay between long-term climate cycles and the El Nino phenomenon. In addition, other studies have shown no significant increases in global hurricane activity over the last 50 - 60 years. Augmenting our own research group's study (4) with hurricane activity from 2000 2004, for example, does not change our results.


What our study did conclude was that hurricane activity, from 1999 on, would be more similar to that of the active period in hurricane occurrences from the 1940s - 1960s and would show little year-to-year variability. So far, the first few years of the current decade have followed this pattern.


So, is the current era of hurricane activity unprecedented? If we look at hurricane activity from 1932 - 1937 (6), we would find that 37 storms occurred in the Atlantic Ocean basin. While this is nine fewer storms over a six year interval than the recent active period cited above, any researcher would concede that the hurricane archives prior to about 1940 are, at best, incomplete.


An examination of hurricane archives from these earlier times almost always show little if any hurricane activity in the east Atlantic, where observations would have been sparse. Thus, it is very possible, or even likely, that the earlier period observed just as many storms. Additionally, it would be hopeless to attempt a comparison of today's intensities to those of the earlier period. Furthermore, how could global warming be used to explain the period 1884 - 1889, when 43 hurricanes were logged as part of the record?


What about the 2005 season-to-date? There was a lot of discussion about the early start to the 2005 hurricane season. At this point in the season, we are not that far ahead of four of the previous five seasons in hurricane occurrences. While there is still the active month of October to go in this hurricane season, it is likely that this season will not see a repeat of the disaster caused by Katrina. But, it only takes one storm such as this one to have such a far reaching impact on our society both in terms of human suffering and the economic hardship that will undoubtedly follow. Invoking global warming as the cause of storms like Katrina and Rita does not help anyone harmed by the storm and causes even more damage to the public discourse on climate change.  


(1) Kluger, J., Is global warming fueling Katrina? Time ( 29 August


(2) Webster P., et al., 2005. Changes in tropical cyclone number, duration, and intensity in a warming environment. Science, 309, 1844-1846.

(3) Michaels, P., Global Warming and Hurricanes: Still no connection.

(4) Lupo, A.R., and G.Johnston, 2000: The variability in Atlantic Ocean Basin hurricane occurrence and intensity as related to ENSO and the North Pacific Oscillation. Nat. Wea. Dig., 24, 3-13.

(5) Tropical Meteorology Project, see comments by Dr. William Gray

(6) Colorado State University hurricane data archives available via


To see more of the extensive coverage of the 2005 Hurricane Season from TCS, click here.


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