There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.

Mark Twain

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Fear Mongering

Yelling fire in a crowded theater is a crime, but only if it incites imminent lawless action. People rushing to the exits may be harmed, but no lawless action was encouraged. So what about yelling climate change during the impact of two large hurricanes? The same thinking applies. People will undoubtedly be harmed by the rush to poor public policy, but no lawless action was encouraged. But just as a snow storm is not evidence against global warming, two large hurricanes are not evidence for climate change, let alone man-made climate change. Anecdotal evidence is unscientific. In terms of recorded data, the current hurricanes are not even that unusual.

Meteorologists had a field day with Hurricanes Harvey and Irma because of their rarity. The continental United States had not had a large hurricane hit land for quite some time. Hurricane Sandy, while devastating to the East Coast, was not a major hurricane by wind or pressure standards. The last significant hurricanes hitting the United States were Katrina and Rita in 2005. Ranking hurricanes by damage is nonsense, judging storms by the foolishness of the building codes and power constructs in their path. A list of the major hurricanes hitting the continental United States since 1900 is instructive.

Note that Irma is tied for the seventh strongest hurricane and Harvey is tied for eighteenth by atmospheric pressure. For reference, the Labor Day Hurricane of 1935 caused storm surge of 18-20 feet in the Florida Keys. The storm surge for Irma was on the order of 10 feet. That is still bad for the Keys.

Other meteorological rankings of hurricanes exist. And the media will always exaggerate the largest to tell a more fearful story. For instance, the accumulated cyclone energy is frequently used. By that standard, Hurricane Irma was the second largest hurricane on modern record because it spent so much time over the warm tropical water with little or no shear to disrupt it. However, the seasonal look at all cyclonic storms puts that in perspective.

Note that some years are higher than others. There is great variability. Note also that this measure requires frequent measurement of wind speed that may not have been as accurate in the older records, and is nonexistent in the earliest years on record. Not many planes flew through a hurricane in 1935.

The longer history of all hurricanes to make landfall in the United States is also interesting. The National Oceanic and Atmospheric Administration (NOAA) keeps a record of all landfalling hurricanes from 1800s to the present.

Note that the data are plotted summed over two decades to reduce the noise and make trends more visible. From this data, the number of landfalling hurricanes appears to decreasing over time. Since climate change is actually measured over a length of time, say 30 years, it would appear that the climate for hurricane formation is becoming more docile.

However, hurricanes, known as cyclones worldwide, make landfall in many places other than the United States. While the history is not as complete, the plot of number of cyclones over 40+ years shows great variability and little trend.

And the same kind of plot for all tropical storms is no different: little or no trend. Remember that tropical storms are just cyclonic storms that have not built up sufficient wind speed to be classified as hurricanes. Sustained winds of 56 mph or greater are needed.

Now to the questions at hand. Is climate change visible in an increase in the number of tropical storms? No. Is climate change visible in an increase in overall storm intensity? The accumulated data is insufficient. Can two hurricanes over 16 days be used to make any statement about climate change? Not honestly, but that hasn’t stopped college professors from making that claim even if their meteorology is wrong.

In trying to correlate hurricanes with climate change, I suppose we could try politics. After all, Presidents do change the climate in a meaningful way. Do hurricanes favor one political side over the other? Possibly, maybe, if you squint, but look at Wilson and Taft. So probably not ;-).

Thanks to NOAA, Ryan Maue, Philip Klotzbach, and Roger Pielke Jr for all the data they freely put in the public sphere.

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