From Dr. Roy Spencer's Global Warming Blog
Author: Dr. Roy W. Spencer
Florida residents must feel like they've been hit by major hurricanes in recent years, but what does the data show?
The problem with human perception of such things is that the time scales at which hurricane activity fluctuates tend to be longer than human experience. For example, people born in the 1950s will not remember that Florida was hit by major hurricanes (five in total) in the 1940s. But they have many memories of the hurricane lull of the 1970s and 1980s, when Florida experienced just one major hurricane each decade. Then, when the number of hurricane strikes increased, they thought something was unusual and they thought “hurricanes are getting worse.”
Another problem is that for an area as small as Florida, any statistics will be quite noisy, even over 100 years. Hurricanes making landfall in the eastern United States will be a better gauge. Statistics are even better for the entire Atlantic basin, except that satellite coverage didn't begin until the 1970s, and hurricane intensity measurements in remote areas were poor (or not measured at all) before then.
Finally, tropical cyclone statistics for the entire tropics would be best (if trying to determine whether climate change affects cyclone intensity or frequency). But satellite data from the global tropics are again limited to the period since the 1970s. Global tropical cyclone data before the 1970s are sketchy at best.
So, keep in mind that any trends we see in Florida will be strongly influenced by the “luck of the lottery” and the quasi-random nature of hurricane paths (hurricanes are guided by massive air currents in the mid-troposphere, say about 20,000 feet height), what are the statistics on the intensity and frequency of major hurricanes in Florida since 1900?
Intensity and number of major hurricanes in Florida
The chart below shows the intensity of major hurricanes (maximum sustained winds of 100 knots or greater) that have struck Florida since 1900, updated with the most recent (2024) Hurricane Helene:
As can be seen from the linear trend line, there is no obvious trend. strength Major hurricanes to hit Florida since 1900.
But so what Digits hurricane? The chart below shows a slight upward trend in the ten-year total of major hurricanes hitting Florida since 1900:
Note that the numbers for the 2020s are likely to increase, as the end of the current (2024) hurricane season is just over halfway through the 2020s. Although Hurricane Milton was just classified as a major hurricane, its wind shear is expected to increase within 2 days, so it is not obvious whether it will hit Florida as a major hurricane, so I did not include it in the chart above.
Another feature of the second chart above shows that Floridians born in the 1960s or 1970s do experience an increase in major hurricanes hitting Florida during their lifetimes. But their first decades of personal experience occurred during a historic lull in hurricane activity.
Why start in 1900?
There is reason to believe that the number and/or intensity of the major hurricanes that struck Florida in the early 1900s were underestimated, which would bias the trend in the above graph upward, falsely indicating a long-term increase in activity. First, in 1900 Florida was virtually uninhabited. A hurricane's intensity is determined by its maximum wind speed lasting one minute and usually covers a very small area. Even though people now live along much of the Florida coastline, coastal anemometers rarely measure hurricane intensity given by the National Hurricane Center because these winds cover such a small area. So how do you know how severe some hurricanes in the early 1900s were?
Evidence for long-term hurricane fluctuations independent of water temperature
Modern concerns are that global warming from man-made carbon dioxide emissions is causing sea surface temperatures to rise, causing hurricanes to become stronger or more frequent. But studies of Gulf Coast and Caribbean coastal lagoon sediments deposited by catastrophic hurricane landfalls show large fluctuations in activity on centennial to millennium time scales, even in the absence of unusually warm sea surface temperatures measured today . (Example here.)
It should also be remembered that not long ago, the United States experienced an “unprecedented” 11-year drought amid major hurricanes. This greatly affects our perception of “normal”. When the lull reached nine years, a NASA study found that such an event would occur only once every 177 years. I recall that when the lull reached 11 years, this number increased to 1 in 250 years.
The point is that there are huge natural variations in hurricane activity in Florida (or any other hurricane-prone state) on decadal to century time scales. But as more and more people think the government is influencing hurricane activity in some way (I see a lot of this on Twitter), I doubt the actual data will have much of an impact on these people, and while I'm on Earth As I pass my 70th year, I notice a long-term decline in critical thinking about weather, climate, and cause and effect. I suspect this trend will change anytime soon.
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