As the Atlantic hurricane season kicks off, millions are anxiously monitoring forecasts and looking for telltale signs of impending storms.

This year promises to be particularly severe. Ocean temperatures remain exceptionally high, and conditions in the Pacific are set to amplify Atlantic storm activity.

However, beyond the immediate forecasts, a more profound and surprising phenomenon is unfolding with tropical cyclones globally.

With rising global temperatures driven by human actions, climate change is reshaping our understanding of storms that batter coastlines. These storms are becoming wetter, more intense, and sometimes extraordinarily powerful. The current classification system for these storms is quickly becoming obsolete.

Indeed, it has been noted that Category 5 hurricanes (the most intense classification on the Saffir-Simpson scale) may no longer represent the upper limit. Future storms could necessitate an entirely new category.

“This is a discussion that has occurred several times, and I believe it is a valid argument,” says Dr. Tom Matthews, a senior lecturer in environmental geography at King’s College London. BBC Science Focus.

“We’ve expanded to Category 5 on the Saffir-Simpson scale, so using the term Category 5 is misleading, and we do need a new category.”

How are hurricanes classified?

Hurricanes are currently classified using the Saffir-Simpson scale, which is based on sustained wind speeds.

• Category 1 – 74-95 mph (119-153 km/h). Very dangerous winds cause minor damage.
• Category 2 – 96-110 mph (154-177 km/h). Very dangerous winds cause significant damage.
• Category 3 – 111-129 mph (178-208 km/h). Catastrophic damage occurs.
• Category 4 – 130-156 mph (209-251 km/h). Catastrophic damage occurs.
• Category 5 – Over 157 mph (over 252 km/h). Catastrophic damage occurs.

However, climate change is pushing storms far beyond these established limits. Hurricane Patricia recorded wind speeds of 215 mph in 2015. Hurricane Dorian in 2019 hovered over the Bahamas with wind speeds of 185 mph.

Additionally, Typhoon Haiyan, highlighted by Matthews as a prime example of these next-generation storms, struck the Philippines in 2013 with sustained winds of 195 mph (314 km/h), with gusts reaching up to 220 mph (354 km/h).

These storms are unlike any we have experienced before.

How is climate change impacting hurricanes?

One might expect that as the planet warms, the number of hurricanes will increase. However, the situation is more nuanced.

“The upper atmosphere warms faster than the lower atmosphere, creating stability that resists the vertical movements essential for hurricane formation,” explains Matthews.

Hurricanes depend on rising air, but a heated atmosphere can suppress this necessary upward movement, making it more difficult to initiate a hurricane.

“It’s akin to trying to lift a hot air balloon when the surrounding atmosphere is warmer than the burner inside the balloon,” Matthews elaborates.

“Another apt analogy is that the atmospheric lid above convection—the vertical movement needed to kickstart a hurricane—is becoming stronger, impeding hurricane development.”

This translates to reduced chances of hurricane formation. Nonetheless, when they do occur, they tend to exhibit explosive intensity.

Mathews provides another perspective: “A hurricane serves as a mechanism for redistributing heat from the ocean to the atmosphere. More heat is needed to initiate a hurricane.”

“This could mean they are less frequent, but when they do occur, they pack a significant punch.”

Moreover, rising sea levels mean that even storms of similar intensity can push further inland, causing greater damage. “Unfortunately, this is an unavoidable reality,” Matthews concludes.

Why is a new category necessary?

The classification of tropical cyclones is not merely an organizational tool; it is crucial for understanding the evolving nature of storms. With storm intensity rising, the current five-level classification may be insufficient for effective assessment.

Even within Category 5, there exists a vast range that can mislead and obstruct preparedness efforts.

“What may seem like a minor change, especially in wind speeds, can correspond to significant differences in damage.”

This dynamic is amplified because the force of wind impacting an object relates to the square of its speed, and the resulting power grows proportionally. In simple terms, what may seem like a minor acceleration can lead to catastrophic consequences on the ground.

“What may appear to be a slight change can cause substantial damage. This is especially problematic when structures are designed to withstand specific wind speeds but are exceeded.”

This is a serious warning. With ongoing climate change, the strongest storms are intensifying, and our longstanding classification system may no longer suffice.

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About our experts

Tom Matthews serves as a senior lecturer in environmental geography at King’s College London, UK. His research delves into extreme meteorological environments and events. He has worked extensively in mountainous regions, such as the Himalayas, where he has been instrumental in setting up state-of-the-art weather stations on Mount Everest. His studies on severe extratropical cyclones and combined events have furthered the understanding of extreme humid thermal events and their prospective changes due to climate warming.