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Hurricane Ian and the new era of rapidly accelerating storms

People walk along the beach in Bonita Springs, Fla., on Thursday to look at the damage left by Hurricane Ian. (Sean Rayford/Getty Images)

One of the reasons that many experts prefer the term “climate change” to “global warming” (beyond the political provenance of the former term) is that “climate change” doesn’t constrain expectations about what might happen as the world gets hotter. The globe will warm, certainly; air temperatures have risen and will continue to rise. But there are myriad other effects, some related to air temperatures and some not.

For example, water temperatures will also rise (and have also risen). That means water will expand, accelerating sea-level rise. Rising air temperatures, meanwhile, mean that air can hold more moisture. Climate change will spur longer, deeper droughts — but also, because the sky contains more moisture, bigger rain- and snowstorms.

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The arrival of Hurricane Ian in Florida this week provides an example of what warmer ocean water and more atmospheric moisture can yield. Writing for Axios, Andrew Freedman described Ian’s rapid intensification as it neared Florida, something that is relatively unusual from a historical perspective but clearly linked to factors correlated to climate change.

As he noted, that storms like Ian are getting stronger faster provides a very real and immediate risk to areas in the hurricane’s path.

“The danger of a rapid intensification shortly before landfall is that people will be caught off guard by the stronger storm,” Freedman wrote, “and get stuck in a vulnerable spot for storm surge flooding, damaging winds or both.”

The National Oceanic and Atmospheric Administration has historical data on the speed and location of hurricanes near the United States. Using this data, segmented into six-hour observation periods, we can get a sense of how the number of rapidly intensifying storms is increasing.

The most a hurricane’s wind speeds have increased over a six-hour window in NOAA’s records was 63 mph. There are 12 storms, though, where speeds have increased by at least 35 mph over that period. Of those 12, seven have occurred since 2000.

If we look at the hurricane data by time periods, we can see the rise in the number of storms in which wind speeds increased rapidly. As a function of the percentage of all six-hour periods catalogued in the NOAA data set, the density of periods in which wind speeds picked up by only 9 mph is down. The percentage in which wind speeds increased by 23 mph or more is up.

Period
5 knots
20 knots or more
1910 to 1939
84%
0.3%
1940 to 1969
77.4
0.6
1970 to 1999
76.1
1.6
2000 to 2021
75.5
2

As you probably noticed, most of the storms in which rapid increases in wind speed occurred were in the Gulf of Mexico or the Caribbean. In nearly every part of those regions, the surface temperature of the water has increased since the early 1960s. On average, the increase across latitude-longitude locations is 1.2 degrees Celsius. That’s more than 2 degrees Fahrenheit.

The largest increase in a hurricane’s wind speed over 24 hours was 95 knots — 109 mph. There are eight storms that have seen 24-hour increases of at least 81 mph. Six of them happened since 2000. Three developed since 2016.

More heat in the ocean to draw from and more atmospheric moisture mean bigger hurricanes. Climate change contributes to both of those factors. And climate change has unquestionably worsened over the past several decades.

Again, this is not an academic exercise. As Freedman points out, a storm that suddenly jumps from Category 4 to Category 5 is a storm that people risk underestimating. And there is perhaps no bigger contributor to deaths during natural disasters than human underestimation of the threat.

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