Scientists are debating adding a Category 6 for mega-storms

In 1973, National Hurricane Center The Saffir–Simpson scale was introduced, a five-category rating system that classified storms based on wind intensity.

At the bottom of the scale was Category 1, for hurricanes with sustained winds of 74 to 95 mph. At the top was Category 5, for disasters with winds of 157 mph or more.

In the half century since the scale began, land and ocean temperatures have steadily increased as a result of greenhouse gas emissions. Storms have become more intense with strong winds and heavy rainfall. This week a research team led by climate scientists at the University of Pennsylvania michael mann Predicted that an unprecedented event will be seen in the North Atlantic 33 named tropical cyclones From 1st June to 30th November.

Some scientists argue that with destructive hurricanes routinely exceeding the 157-mph threshold, the Saffir–Simpson scale no longer adequately expresses the threat of the largest hurricanes that exist.

Earlier this year, two climate scientists published a paper which compared historical hurricane activity to a hypothetical version of the Saffir–Simpson scale, which included a Category 6 for hurricanes with sustained winds of 192 mph or greater.

Of the 197 typhoons classified as Category 5 from 1980 to 2021, five fit the description of a hypothetical Category 6 typhoon: Typhoon Haiyan in 2013, Typhoon Patricia in 2015, Typhoon Meranti in 2016, Typhoon Goni in 2020, and Typhoon Surigae in 2021. . ,

Patricia, which made landfall near Jalisco, Mexico in October 2015, is the most powerful tropical cyclone ever recorded in terms of maximum sustained winds. (While the paper looked at global hurricanes, only hurricanes in the Atlantic Ocean and the North Pacific Ocean east of the International Date Line are officially ranked on the Saffir–Simpson scale. Other parts of the world use different classification systems. )

Although the storm had weakened to a Category 4 by the time it made landfall, it still had sustained winds of 215 mph over the Pacific Ocean.

“It’s kind of beyond comprehension,” said Michael F. wehner, a senior scientist at Lawrence Berkeley National Laboratory and co-author of the Category 6 paper. “It’s faster than a straight-up racing car. This is a new and dangerous world.”

In their paper, which was published in the Proceedings of the National Academy of Sciences, Wehner and co-authors James P. Kosin The University of Wisconsin–Madison did not explicitly call for the adoption of Category 6, primarily because the scale is being replaced by other measurement tools that more accurately measure the threat of a specific hurricane.

“The Saffir-Simpson scale is not that good at warning the public about the imminent threat of a hurricane,” Wehner said.

The category scale only measures sustained wind speed, which is one of the dangers of a major hurricane. National Hurricane Center Director Mike Brennan said during a recent public meeting that of the 455 direct deaths in the U.S. due to hurricanes from 2013 to 2023 — a figure that does not include deaths from 2017’s Hurricane Maria — 15%. Less than 100 km/h were caused by wind. The rest were caused by storms, floods and tides.

The Saffir-Simpson scale is a relic of an earlier era in forecasting, Brennan said.

“Thirty years ago, basically all we could tell you about a storm was how powerful it was at the moment. We couldn’t really tell you much about where it was going to go, or how strong it was going to be, or what the threats were going to look like,” Brennan said during the meeting, which was organized by the American Meteorological Society. “Now we can tell people a lot more than this.”

He confirmed that the National Hurricane Center has no plans to introduce a Category 6, primarily because it is already trying to “not push the scale too far,” Brennan said. Other meteorologists said it was the right decision.

“I don’t see any value in it at this time,” said mark bourassaMeteorologist at Florida State University’s Center for Ocean-Atmospheric Prediction Studies. “There are other issues that could be better addressed, such as the spatial extent of hurricanes and storm surges, which would provide more useful information [and] “Assist with emergency management as well as individual people’s decisions.”

As simple as they are, Herbert Saffir and Robert Simpson’s categories are the first thing many people think of when they try to understand the scale of hurricanes. In this sense, the continuity of the scale over the years helps people understand how much the climate has changed since its inception.

“What the Saffir-Simpson scale is good for is quantifying, showing that the most intense hurricanes are becoming more intense because of climate change,” Wehner said. “It’s not like it used to be.”