As the second brutal storm in the past few weeks bears down on Florida, it’s worth looking at the relationship between climate change and hurricane season. Hurricane Milton has already broken some records, rapidly intensifying into a Category 5 hurricane before weakening a bit. It’s perhaps a bit too easy to, in this age of American empires in decline, shrug it off and say, “Welp! What are to do!?” Perhaps we can start by asking some basic questions. Is climate change exacerbating the rate at which we experience hurricanes? Is it making hurricanes worse? And, importantly, how is it doing this?
How does Milton stack up?
Formed on October 5th, Milton quickly became the fifth most intense storm ever recorded, after Rita (2005), the Labor Day hurricane of 1935 (which famously destroyed Henry Flagler’s Key West railroad), Gilbert (1988), and Wilma (also 2005). If you said, “gee, that’s a whole lot of storms in 2005– also, wasn’t Katrina in 2005?” then you’d be correct! Five of the most intense ten hurricanes on record have occurred in the past twenty years.
First, one challenge with historical data is that we have only had relatively consistent, comprehensive, and uniform meteorological data for the past half century. Let’s recall that outside measurements of things like temperature, standardization is a relatively novel concept. We have pretty good numbers from the past hundred-ish years, though. Climate scientists look not only at historical temperature records but plenty of other records– historical water levels, historical levels of carbon dioxide, and other stuff that can’t be measured through historical records but rather through, ahem, deep science.
If you measure by damages rather than meteorological intensity, on the other hand, all ten of the most damaging hurricanes have occurred in the past twenty years. This is, as I tell my students all the time, true but unconnected to the specific question of storm intensity or climate change– the damages are substantially attributable to the fact that we have allowed unchecked urban development in the Gulf Coast, where hurricanes are likely to inflict the most damage. This is why it’s silly to talk about how the increased incidence of billion-dollar storm events are evidence of climate change. They are indeed evidence of climate change having huge economic effects, but not evidence of climate change itself, of course. They’re also evidence of how insurance markets are, well, fucked, basically– the average homeowner is now paying nearly $12,000 a year for insurance (that is approximately what we have paid for our house in Detroit for six years).
What does the science say?
For one, we know that the Gulf of Mexico has been abnormally warm as of late– and appears to be warming faster than other parts of the ocean. We suspect that this is because of climate change, which, most scientists agree, is the product of an abnormal (extreme) increase in the rate of carbon dioxide from the ceaseless combustion of fossil fuels. That’s a problem, because temperature changes make storms worse. And how, you ask?
Simply put, warmer air can hold more moisture than cooler air.
For every unit of increased temperature, air has a fixed rate of additional capacity for moisture. How much, you ask? About 7% increased moisture capacity for every degree of temperature (°C). This is established by an equation called the Clausius-Clapeyron Relation. An idea originally devised notionally by Sadi Carnot (inventor of the Carnot Cycle and basically the entire field of thermodynamics), Clausius-Clapeyron establishes a curve that illustrates the phase transition of vapor along axes of temperature and pressure. This is called the Coexistence Curve because of the notion of vapor and liquid coexisting along opposite sides of this curve in equilibrium. They’re friends!
How does it play out for a hurricane?
Illustration
Imagine that a storm holds 100 billion gallons of water (a nice, round number!). If the temperature increases by 3°C (the aspirational limit of warming from baseline temperatures set by global climate treaties), this means that the theoretical storm in the warmer world can now hold about 123 billion gallons. Every degree C increased means an additional 7%, and this additional capacity is, of course, cumulative. Now, think that we’re talking about an average of 3°C. This means that you might have temperature swings that push that number to, say, 10°C above historical averages. That gives us 197 billion gallons of water.
With Florida ocean temperatures hitting record highs of hot tub temperatures in 2023, we can see how this theory can become reality. Or how Category 5 storms can be come more common. Or perhaps how the categories could become somewhat irrelevant when wind speeds increase to the point that a Category 5 inevitably becomes a Category 6. And so on and so forth.
There’s a lot we don’t know about climate science, of course. We do know that the Clausius-Clapeyron Relation explains how warmer temperatures can translate to more intense storms. We also know that more damaging storms occur as development in storm-prone areas proliferates. This is a bad thing, because we do not have the resources to adapt every square inch of the built environment, strip malls and all, to the inevitability of climate doom. So, this will lead to some tough questions about how to restrict growth that, you can imagine, will go over great with folks like Ron DeSantis. In the meantime, I am hoping that all of our friends in Florida are staying safe.