In a 2C global warming scenario, the risk of Category 6 storms would double in the Gulf of Mexico and increase by 50% near the Philippines.
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The Saffir-Simpson hurricane wind scale, the most widely recognized risk assessment method for tropical cyclones, is no longer accurate in measuring the climate change-driven exponential increase in winds, a new paper argues.
Developed in 1971 by civil engineer Herbert Saffir and meteorologist Robert Simpson and introduced to the general public in 1973, the scale classifies hurricanes into five categories based on their sustained winds. To be classified as a hurricane, a storm must have a one-minute-average maximum sustained winds of at least 74 mph or 119 km/h (Category 1). Currently, the highest classification is assigned to storms with winds blowing at a speed of at least 157 mph or 252 km/h (Category 5). The scale also estimates the extent of potential damage to properties, infrastructure, and livelihoods, with Categories 3-5 hurricanes – also known as major hurricanes – expected to cause “devastating” to “catastrophic” damage and loss due to the strength of their winds, though it does not take potentially deadly hazards such as storm surge, rainfall flooding, and tornadoes into account.
However, a new paper published Monday in the Proceedings of the National Academy of Sciences (PNAS) argues that the Saffir-Simpson scale needs updating to reflect the exponential increase in wind intensity witnessed in recent years. According to Michael Wehner and James Kossin, who are behind a assessment, the fact that the scale is open-ended – meaning that anything beyond 157 mph or 252 km/h is classified as Category 5 and assigned the same level of wind hazard – reflects a flaw in the system, no matter if it is blowing 160 mph (257 km/h), like 2022 Hurricane Ian in the US, or 215 mph (346 km/h), like Mexico’s 2015 Hurricane Patricia.
“What we found is that the strongest storms have become stronger because of climate change … and we thought that highlighting that reality by adding another category to the scale would raise awareness of the increased danger of climate change regarding tropical cyclones and hurricanes,” Weiner said in a radio interview with WCBS.
Hurricanes – also known as typhoons in the northwestern Pacific and cyclones in the Indian Ocean and South Pacific – are a rather common weather phenomenon, though there has been a significant increase in their intensity in recent decades, which scientific observations link to anthropogenic climate change.
These abnormal trends are attributed largely to the increased ocean temperatures – warmer than normal Atlantic waters. Indeed, as ocean surfaces warm, so does the air above it, causing water to be carried up to high altitudes to form clouds, while leaving a low pressure zone beneath causing more air to rush in. As these systems build up, thunderstorms are formed, and if there are no strong winds to slow it down, they can become hurricanes.
A 2020 analysis of satellite records from 1979 to 2017 found that the likelihood of a storm reaching Category 3 or above, with sustained winds of 185 km/h, increased by 8% per decade. In 2023, the Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (AR6) confirmed these observations, arguing that the proportion of Category 3-5 tropical cyclones as well as the frequency of rapid intensification events have likely increased globally over the past four decades.
For this reason, Wehner and Kossin suggest adding a hypothetical new category – Category 6 – to the Saffir-Simpson. The new category, they argue, would reflects changes in wind speeds, which have already been reached in a number of recent storms, all of which happened in the last decade, including Typhoon Haiyan (2013), Typhoon Meranti (2016), Typhoon Goni (2020), and Typhoon Surigae (2021) in the Western Pacific and Hurricane Patricia (2015) in the Eastern Pacific.
And with our atmosphere and oceans set to continue warming in the coming years as the climate crisis intensifies, there is little doubt that wind speeds will also progressively strengthen. In fact, Kossin and Wehner’s future climate models suggest that, in a 2C global warming scenario, the risk of Category 6 storms would double in the Gulf of Mexico and increase by 50% near the Philippines.
More on the topic: How Does Climate Change Affect Hurricanes?
