Unraveling Hollywood's latest spin on tornadoes

There is a scene in the movie "Twisters" in which the main character's mother, an Oklahoma farmer, remarks how she keeps seeing more tornadoes and floods and droughts. Given the proliferation of natural disaster images on television or in our social media feeds, her assessment may have struck a chord with many theatre-goers this past summer.

As a meteorologist and climate researcher who models the forces that drive insurance losses from weather-related catastrophes, however, I thought it worth pointing out that the film's conclusion about the frequency of these natural disasters, at least from what we know now, is only two-thirds correct.  

Droughts and flooding in many parts of the world are growing more frequent and intense. Data gathered and analysed by my colleagues at Swiss Re indicates climate change is exacerbating both of these perils, bringing too much water to some places and too little to others. The movie got that right, even if it stopped short of citing the role of a warming planet.

With tornadoes, it's more complicated. Ascertaining their trajectory – whether we are seeing more of these violently rotating columns of air, and whether they are likely to become more powerful – comes with far less certainty. There is no clear consensus whether tornadoes, often produced by severe convective storms (SCS) that also bring heavy rain and large hailstones that represent a big threat to property, are growing more frequent or fierce with a changing climate.

Tornadoes require a complex mix of atmospheric ingredients to form, including warm, moist air near the ground, cooler, drier air at higher altitudes, and wind shear, where wind changes speed and direction with height. While often short-lived, they sometimes hit suddenly and with extreme intensity.

Some evidence suggests tornado risk may actually have diminished in the US Southern Plains region known as "Tornado Alley" while amplifying to the east and southeast. Still, researchers are still examining whether changes in thunderstorm behaviour can be attributed to global warming, or whether perceived trends are instead due to natural variability.

While reports of tornadoes do seem to have grown more common, that may be due to the always-on news cycle and the nature of our online lives. Moreover, the instruments scientists have at their disposal to identify, record and study tornado-producing thunderstorms are also improving; we can observe more tornadoes, even if there aren't necessarily more of them.

Modelling tornadoes is also very challenging. As our atmosphere warms, we can expect greater instability that can produce powerful supercell thunderstorms. Still, there is also likely to be less wind shear, which is needed to create the rotating updrafts that spawn tornadoes. In short, meteorological forces are sometimes locked in competition and we are not yet certain which will prevail.

So, while it is premature to say we're experiencing more tornadoes and the severe thunderstorms that produce them, other powerful trends linked to these destructive weather events are much clearer. In the United States, insured losses from severe convective storms, in particular from hail, have been rising at a rate of about 8 percent annually since 2008, according to Swiss Re Institute calculations.

These losses are not driven primarily by climate-related hazard intensification, but rather economic growth, urbanisation, ageing roofs and vulnerable facades, as well as expansion of valuable assets like photovoltaic solar panels. Put simply, we have more people and property in harm's way. With inflation supercharging losses, the consequences haven't come cheap.

In 2023 and the first half of 2024, global insured losses from severe thunderstorms added up to USD 106 billion, exceeding damages from all other natural catastrophes combined, including earthquakes and hurricanes. Rising SCS-related losses, in North America but also in Europe and Asia, are a clear sign that communities virtually everywhere must harden their defenses.

From that perspective, the need to adapt to severe thunderstorms, tornadoes and hail, regardless of these perils' future trajectory, is not so different from what is also necessary to prepare for intensifying floods and drought. 

First and foremost, to protect human life, tornado country residents should have emergency plans in place, so they can react quickly when storm warnings come. Building codes in regions exposed to tornadoes and hail should also reflect the current risk environment. We know that when structures are rebuilt to storm-resistant standards after a destructive event, they fare better when subsequent tornadoes hit.  

Impact-resistant roof coverings, skylights and windows are needed, as are roof slopes engineered to minimise hail's destructive potential. Similarly, solar panels, whether on rooftops or in utility-scale installations, must be durable enough to survive direct hits, securely mounted and properly maintained. Automatic PV panel covers and technology to adjust panel angles can add to up-front costs but will likely pay dividends during a severe hail event.

For reinsurers and insurers, monitoring building trends, keeping tabs on inflation and updating models accordingly are all key to delivering risk information that insurance buyers need to mitigate their exposures. This includes tracking how exposures evolve with construction patterns while working proactively to accurately value clients' assets. After a thunderstorm is not the time to learn the replacement cost is more than originally anticipated.

Hollywood didn't get everything quite right when it resurrected the disaster genre this summer. But its latest spin on tornadoes did open an opportune window for engaging in a broader discussion of natural catastrophe losses, what's really driving them, and how to protect people and property, regardless of what the future brings.

To that end, another scene from "Twisters" stayed with me, too. It's the one where the actor Glen Powell's character describes the forces that produce tornadoes as "a mix of what we know, and everything we can't understand." That may be true, but the science is advancing. We're learning more every day. And as our understanding grows, so must our efforts to build resilience.