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Hurricanes 100 years later — it isn't all about the number

Hurricanes 100 years later — it isn't all about the number
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Hurricanes exist for a reason. How many we have and how fast the winds become are related to why they exist. But they are separate characteristics of the same event. While hurricane scientists would agree that there are no more hurricanes today than there were 100 years ago, why hurricanes exist and the frequency with which they hit isn’t quite so simple and shouldn’t be ignored.

One characteristic of hurricanes refers to the frequency — will we see more/less hurricanes this summer than last? The other refers to the intensity — will the storm reach Category 5 status like Hurricane Michael in 2018, or only a Category 1, with milder winds?

Our planet is unequally heated, as evidenced from the ice-covered surface of the poles and the blue skies and palm trees of the tropics. This unequal heating forces air to move due to something called the pressure gradient force. You know this movement as the wind. If this process didn’t occur, you would see the tropics become continuously hotter and the poles continuously colder. Instead, we see the tropical temperature remain the same on a daily basis. Hot and, typically, humid. The ice-cover of the poles do not continuously expand, but instead, slowly melt due to the influx of energy brought by the wind. Hurricanes are the ultimate heat transporters on our planet. They are the manifestations of the surplus heating within the tropics into swirling energy transport systems. That energy is then moved from its original location within the tropics to areas all around the subtropics, midlatitudes and poles, as the systems ultimately leave their origin points and begin to dissipate at higher latitudes. 

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How many hurricanes we see develop — the frequency — depends on whether the atmospheric conditions are conducive to the continued formation and ultimate tracking to the U.S. coast. There are many factors impacting frequency, like stratospheric wind changes, changes in tropical wind patterns and changes in air pressure and sea temperature over the Pacific Ocean — events known as El Niños or La Niñas. Climate change is also a factor. 

Many critics of climate change state the number, or frequency, of these energy transport systems are not changing over time. The number of storms across the globe that we have today is no different than the number of storms we had 100 years ago. Many hurricane scientists would agree with that statement. The number of total storms really hasn’t changed. However, thinking of overall frequency as the only potential mechanism for showcasing climate change is misleading. 

If the number of storms isn’t changing, but there is more energy on the planet, how else might that manifest where humans notice a change? The maximum potential intensity of a hurricane is something that has been theorized about since the 1980s. How strong can a given hurricane actually get? That strength is related to the amount of energy available in the atmosphere and oceans, which is also related to those oscillation patterns and climate change. In a world where we have more of a capacity to hold onto energy, the energy must be transported. So, in a warmer environment, we might not see the total number of storms change, but if we break it down by intensity, we begin to notice a shift to a more intense hurricane environment. For two decades scientific research has suggested that the most extreme hurricanes are becoming more extreme. What does this mean? More storms are reaching higher categories than they used to. Instead of mostly Category 1 and 2 storms, we now see more Category 3, 4 and 5 storms. In fact, it was modeled this would happen a decade ago. In total, the number is the same. But the reality is, the storms that are coming are closer to that theoretical maximum than they used to be — all because we have more energy to transport. The difference is nuanced, and discussions can be misleading when description lacks the important details. 

Frequency is affected by the atmospheric set up. Are all the puzzle pieces in the right spots to make a storm survive? Intensity is additionally affected by energy availability. All else being equal, more energy to transport means a stronger storm. 

What does this mean for us? We have millions of people living along the coastlines. We need to begin accepting that these risks are not going away, nor are they going to improve. The reality is with every additional house built and tree removed, the water dynamics of the coastline change. Instead of spending resources arguing over whether it is or is not changing, solution-oriented approaches should be entertained. In what ways can we make a more resilient coastline in the face of more extreme storms? Education, outreach, sea walls and adequate response after an event. 

Hurricane Delta made landfall just 14 miles away from where Hurricane Laura struck just six weeks ago. The vast majority of homes still standing after Laura had tarped roofs as they waited for help that has been slow to come. Peak wind gusts from Delta in Lake Charles were recorded at 96 mph. Imagine the terror after dealing with one storm to watch your tarped roof blow into yet, another, swirling energy transporter. Those people don’t care, nor should they, about scientists and politicians’ inability to agree on the changing climate. They are living it. And they are waiting for help. Let’s hope it comes.

Jill Trepanier is a hurricane climatologist and associate professor of Geography and Anthropology at Louisiana State University with expertise in the geographic variability of extreme hurricane characteristics.