For more than half a century, the National Hurricane Center has used the Saffir-Simpson wind scale to communicate potential property damage; this system classifies hurricanes on a scale from Category 1 (wind speed 74-95 mph) to Category 5 (wind speed greater than 158 mph).

But as rising ocean temperatures fuel increasingly intense and destructive hurricanes, climate scientists Michael Wehner of Lawrence Berkeley National Laboratory (Berkeley Lab) and James Kossin of the First Street Foundation wonder whether a clear Category 5 is enough to signal a risk of hurricane damage. did. warming of the climate. So they researched and detailed their extensive research. Proceedings of the National Academy of Sciences (PNAS) also introduce a hypothetical category 6, which would include storms with higher wind speeds on the Saffir-Simpson wind scale. More than 192 miles.

Motivation to re-evaluate the Saffir-Simpson scale.

“Our motivation is to review how the openness of the Saffir-Simpson scale can lead to underestimation of risk, and particularly how this underestimation becomes increasingly problematic in a warming world,” said Wehner, who has devoted his career to this work. the behavior of extreme weather events in a changing climate and the extent to which human influence affects individual events.

Anthropogenic global warming significantly increases surface ocean and troposphere air temperatures in areas where hurricanes, tropical cyclones and typhoons form and propagate, providing additional heat energy to fuel the storm, Vener said. When the team analyzed historical hurricane data from 1980 through 2021, they found five storms that could be classified as Category 6, all of which occurred in the last nine years. They determined a hypothetical upper limit for Category 5 hurricanes by looking at the widening range of wind speeds among lower category storms.

Understanding hurricanes and their projected impacts on climate

Hurricanes, tropical storms, and typhoons are essentially the same weather phenomenon; The difference in their names is purely geographical: Storms in the North Atlantic and Northeast Pacific Oceans are called hurricanes, events in the Northwest Pacific Ocean are called typhoons, and events in the South Pacific and Indian Oceans are called tropical cyclones.

In addition to examining the past, researchers also analyzed simulations to examine how a warming climate would affect hurricane strength. Their models showed that as global warming increases to two degrees Celsius above pre-industrial levels, the risk of Category 6 storms increases by 50% near the Philippines and doubles in the Gulf of Mexico, with the highest risk of these storms occurring in the Southeast. . Asia, the Philippines and the Gulf of Mexico.

“Even under the relatively low global warming targets set by the Paris Agreement, which aims to limit global warming to just 1.5°C above pre-industrial temperatures by the end of this century, the increased chance of Category 6 storms is meaningful in these simulations.” ” said Wehner.

“Communicating tropical hurricane risks is a hot topic, and changes are needed in messaging to better inform the public about inland flooding and storm surges, events where the wind scale matters little. While adding a Category 6 to the Saffir-Simpson Hurricane Wind Scale will not solve the problem, It can raise awareness about the dangers of the increased risk of major hurricanes due to global warming,” Kossin said. “The purpose of our results is not to suggest changes of this magnitude, but rather to raise awareness that wind hazards from storms that are currently Category 5 are increasing and will continue to increase under climate change.”