Concerns have risen over the increased intensity of hurricanes due to the climate crisis. Tom Knutson, senior scientist at NOAA’s Geophysical Fluid Dynamics Laboratory, is a leading scientist on hurricanes and climate change. According to Knutson, while models show no change or decrease in hurricane frequency in a warmer climate, a greater proportion of these storms will reach higher intensity levels, giving them a greater chance to become category 4 or 5 hurricanes. However, a handful of super-powerful hurricanes which have occurred in the last decade have led experts to discuss the proposal of adding a Category 6 to the Saffir-Simpson scale.
The Saffir-Simpson scale was introduced in the early 1970s by structural engineer Herbert Saffir and meteorologist Robert Simpson. This scale has become the most common metric in disseminating information to the general public surrounding levels of wind hazard that a hurricane/tropical cyclone poses. The categories range from Category 1, with wind speeds of 74-95 mph to Category 5, with wind speeds exceeding 157 mph.
A figure showing the Saffir-Simpson scale from categories 1-5
A new study, published by two climate scientists Michael Wehner and James Kossin in the Proceedings of the National Academy of Sciences, critiques the openness of the Saffir-Simpson scale proposing an extension by adding an extra category, in a bid to reduce the underestimation of risk by the general public. They have proposed Category 5 should include hurricanes with maximum sustained winds of 157-192mph with Category 6 including hurricanes with wind speeds over 192mph.
If this scale were to be implemented, Category 6 hurricanes would be a rare sight for now. In the past decade, there have been five storms that have exceeded the proposed Category 6 range. This included Typhoon Haiyan, which hit the Philippines in 2013, with wind speeds of 195mph, killing more than 6000 people. Scientists in Taiwan at the time argued for a reclassification of Haiyan into a category of its own. Other storms that fit the category would be 2015’s Hurricane Patricia, which hit Mexico with a top speed of 215 mph and three typhoons in 2016, 2020 and 2021 which formed close to the Philippines.
Although the idea of adding a new category to the Saffir-Simpson scales seems like a non-controversial idea there has been some scepticism and criticism of the proposal. Jamie Rhome, deputy director of the National Hurricane Centre, said his office tries “to steer the focus toward the individual hazards, which include storm surge, wind, rainfall, tornadoes and rip currents, instead of the particular category of the storm, which only provides information about the hazard from wind. Category 5 on the Saffir-Simpson scale already captures ‘catastrophic damage’ from wind so it’s not clear there would be a need for another category even if the storms were to get stronger.” Furthermore, some scientists argue that if a Category 6 level came into place it would diminish the impact of a Category 5.
Deirdre Byrne, a NOAA oceanographer who studies ocean heat and its role in hurricane intensification states, that water-related hazards from hurricanes cause the most threat, further going to say that while adding a Category 6 isn’t inappropriate, combining the Saffir-Simpson scale with a rating for levels of inundation threats might have a greater impact.
Kossin and Wehner said their research didn’t suggest that Category 6 should be added stating, that they intended to convey just how much global warming has dramatically influenced hurricanes. The scientists stated that they hoped their research would raise discussions on how to better prepare coastal communities for extreme weather events.
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