You’re Thinking About Hurricanes All Wrong
Yes they’re caused by climate change—but not as you know it.
Today’s article, by our contributing editor (and resident climate guru) Quico Toro, is the latest installment of our occasional series “Lies, Damned Lies, and Statistics.” The idea of these articles is to critically examine ideas that are prominent in our discourse even though they are wrong or misleading. Click here to read John McWhorter’s earlier entry on the myth of low black esteem, and Zaid Jilani’s article on fallacies about diversity in the workplace.
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Are hurricanes getting more intense due to climate change? This is one of those questions that seems straightforward—almost banal—but gets weirder the closer you look into it. The discussion atmospheric scientists are having about the drivers of the trend towards stronger hurricanes has shockingly little in common with the simplified story you get in the press.
The standard media narrative begins by comparing hurricane trends so far this century with the three preceding decades. They stress that sea surface temperatures have risen substantially since the late 20th century, and warm oceans are hurricane fuel: the hotter the ocean, the stronger the storm.
“Warm Air and Warm Oceans Power Storms Like Debby,” ran a New York Times headline this summer. Last week, Axios reported that “Due to warming ocean waters and air temperatures from human emissions of greenhouse gasses, tropical storms and hurricanes are now delivering heavier precipitation than just a few decades ago.”
The message is that there’s a nice, neat, clean relationship: more greenhouse gas emissions means a hotter planet, which means warmer oceans, which means stronger hurricanes.
The end.
But this story isn’t quite right. The first indication that something is amiss has to do with the reference period. Hurricanes so far this century have indeed been stronger than those in the 1960s through the 1990s. But then, the 1960s through the 1990s were far from normal. As one paper points out, during the 33-year period from 1933 to 1965, 11 major hurricanes made landfall, while during the following 38-year period from 1966 to 2003, only one major hurricane made landfall—Andrew in 1992.
In fact, an influential study published in 2021 by a team of researchers at Princeton and the National Oceanic and Atmospheric Administration shows clearly how odd the period between 1960s and the early 1990s was:
Climate researchers describe that quiet period as the Hurricane Lull. A fairly large academic literature has tried to explain it. And the leading explanation both for the lull and the spike that came after it does have a lot to do with human activity—but nothing to do with the greenhouse effect.
The most up-to-date theories have focused on human emissions, not of greenhouse gasses, but of old-fashioned air pollution: soot, sulfur dioxide, all the gunk that came out of tailpipes and smokestacks in great volumes before the era of catalytic converters and clean air laws.
Alongside the industrial boom of the post-war era, this kind of pollution exploded—wreaking havoc with human health and damaging all sorts of ecosystems. Beyond their nasty health effects, aerosols have a second effect that scientists are increasingly interested in: they reflect some solar radiation back out to space, acting like microscopic parasols to cool whatever is beneath them.
Cooling, not warming.
During the postwar boom, aerosol pollution was emitted mostly in the Northern Hemisphere, where most people live and where most industry is situated. Research now shows conclusively that during the Hurricane Lull of the 1960s-1990s, aerosols were much denser over the Northern Hemisphere. The theory is that the first-order effects of these aerosols accounted for a large proportion of the ocean cooling—and subsequent decrease in hurricane activity—we saw during that period.
But there were second-order effects, too. The atmospheric imbalance seems to have set off a number of unforeseen changes in the climate around the world, altering rain patterns throughout the tropics and, for example, setting off a multi-decade drought over the Sahel region of Africa that caused famine and mass migration.
A recent paper by MIT doctoral student Raphaël Rousseau-Rizzi and his advisor, Kerry Emanuel—one of America’s most respected hurricane specialists—suggests the two may be intimately connected. The mechanism linking them, they argue, was dust in the wind. Literally.
Each year, winds over Africa pick up thousands of tons of dust and sand from Africa and carry it thousands of miles west, depositing it around the Caribbean basin. This so-called Saharan Air Layer also cools whatever is beneath it: for climate purposes, dust is just another heat-shielding aerosol. Rousseau-Rizzi and Emanuel show that dust over the Caribbean is closely related to rain conditions in the Sahel, and conclude that this mechanism is responsible for around half the decline in hurricane strength witnessed during the 1960s-1990s Hurricane Lull.
Emanuel has argued that it was European air pollution that set the entire chain of events in motion, making the Sahel not just dryer but also dustier, cooling the Atlantic during hurricane season, and setting off the Hurricane Lull in the first place. In other words, one set of aerosols, those emitted in Europe, kickstarted a process that led to a massive increase in another set of aerosols—dust clouds from Africa.
This suggests a radically different interpretation of the recent trend towards stronger hurricanes. Rather than being a direct result of global warming, the stronger hurricanes we’re seeing this century may be largely a reversion to the mean: just a return to the pre-1960s norm, when there was less dust and less aerosol pollution cooling the Atlantic.
Now that Europe has largely cleaned up its air, remote sensing data has picked up unambiguous evidence that the rains are back in the Sahel, which is getting greener. A wetter, greener Sahel, though, is a less dusty Sahel, and a less dusty Sahel makes for a hotter Atlantic better able to sustain more powerful hurricanes of the sort we keep witnessing.
Why climate activists would prefer not to dwell on this explanation is obvious enough: it suggests stronger hurricanes are, in some measure, an unintended outcome of European clean air laws.
And the trend is accelerating. Recent changes to maritime shipping regulations suggest much stronger hurricanes could be just around the corner. Since 2020, the International Maritime Organization has implemented tough new standards to clean up the fuels tankers and container ships use, leading to a fast reduction of sulfur dioxide pollution over the Atlantic. The rub is that sulfur dioxide, aside from causing acid rain, acts as a powerful heat shield. By reducing maritime shipping pollution, we’ve radically cut back on the airborne particles that for decades shielded the North Atlantic from the sun.
This is likely to be part of the reason for the unprecedented Atlantic sea surface heat waves that we’ve seen in the 2020s: the proximate cause of the string of strong hurricanes that hit the Atlantic this summer.
But if you listen to mainstream climate journalism it’s easy to get the sense that the greenhouse effect is the alpha and the omega of our influence on the climate. This bears little relationship to the discussion among actual scientists, who are much more comfortable with the idea that human activity affects the climate through many channels at once. The greenhouse effect is fundamental, yes, but it is not the only mechanism: anthropogenic changes to albedo—the amount of heat the Earth reflects rather than absorbs—is also a fundamental driver of the climate.
The inconvenient truth is that sometimes policies to reduce pollution also decrease albedo and accelerate warming.
No advocacy organization will ever want to highlight that, and few journalists will take the trouble to ferret out the fact on their own. The aerosol link gets politely swept under the rug, and the resulting story is much easier for readers to digest: morally unambiguous, with clear good guys and bad guys, little complexity, and a righteous call to action.
The climate movement has put together an appealing narrative, no doubt. Simple and neat. Alas, it’s not scientific. And it’s not true.
Quico Toro is a contributing editor at Persuasion and writes the Substack One Percent Brighter.
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Easily the best science article I've come across at Persuasion.
If we view the historic increase in SO2 and particulate emissions as "experiments" in climate modification that worked, and did not cause any disaster, could that be used as an argument that we should not shy away from the much, much smaller deliberate experiments being proposed to find out if we could counter global warming, given our failures with UN climate agreements?
Fascinating article. There still much to learn about climate change. Perhaps someone will research why the Canadian polar bear population is increasing, all due respect to the BBC.