Friday, September 02, 2005


In the aftermath of Katrina, there's been a lot of talk about global warming and whether or not it has contributed to the severity of hurricanes in recent years. One the denial side, Jonah Goldberg argues that the numbers of category 3,4, and 5 hurricanes haven't increased. He points to this data and says, "[e]ven a casual glimpse at the data provided by the national weather service shows that big hurricanes (categories 3,4, and 5) haven't increased over the 20th century." The problem is that global warming is subtle and you have to do a bit more than just a "casual glimpse."

Using that same data Goldberg points to, I did an analysis of the average strength of hurricanes per decade. Disclaimer: I did make two changes to the data for the 2001-present decade. First, after looking through the climate reports for 2001-2004, I found that there should be 3 category 1 (Gabrielle, Gustav, Claudette) and 3 category 2 (Lili, Isabel, Frances). I also added the two from this year (Dennis as a 4, Katrina as a 5). Here are my findings:

1851-1860 = 19 for 1.9
1861-1870 = 15 for 1.5
1871-1880 = 20 for 2
1881-1890 = 22 for 1.9
1891-1900 = 21 for 2.1
1901-1910 = 18 for 1.7
1911-1920 = 21 for 2
1921-1930 = 13 for 2.2
1931-1940 = 19 for 2.4
1941-1950 = 24 for 2.1
1951-1960 = 17 for 2.2
1961-1970 = 14 for 2.4
1971-1980 = 12 for 1.8
1981-1990 = 15 for 1.8
1991-2000 = 15 for 2.3
2001-2010 = 11 for 2.5

Look at that data. In the past 100 years, we've had two decades that averaged below an intensity of 2. Three of the four highest averages are in the past five decades. Granted, the 2001-2010 average must be taken with a grain of salt because the decade is only half over. I also find it curious that the two decades with the lowest averages (1971-1990) immediately followed the founding of the EPA and the beginning of federal work in protecting the environment. And, of course, there were the gas shortages in the '70s. I don't have the training or the research to state that these correlations mean anything. I simply find these facts interesting.

I am not a climatologist and make no claim to be one. However, from the reports that I have read, I firmly believe that global warming exists and is a factor in the increasing intensity of hurricanes. When I look at the data above, I see a general trend, despite the dip in the '70s and '80s. I think the only thing that would convince Jonah Goldberg would be a category 5 developing a voice box as it passes over his house, calling out "Global warming did this." Even then, he might think it was just the wind and a coincidence.

Update: I just wanted to put a little note in here about the data referred to above. Those are counts of the numbers of hurricanes that hit the mainland U.S. with that category. Hence, Ivan gets counted as a 3, even though it spent a lot of time as a 5 (to which Cuba and the Cayman Islands can attest). So a definitive analysis on trends of hurricane severity would rely on additional data, most of which is not available. Somehow, I doubt people in 1875 were keeping track of the severity of hurricanes that never made it out of the Atlantic.


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