When meteorologists began using the five-step Saffir-Simpson scale to measure the intensity of hurricanes in the 1970s, a Category 5 storm represented forgetfulness. Such a tornado, with sustained winds of at least 157 mph, could have flattened any structure of that era, so there was no reason to give the most ferocious class of tornadoes an upper limit.
Hurricanes have become so intense, scientists are proposing Category 6
by rfergusonlaw.com ·
But as the planet warms, storms are increasingly exceeding what was previously considered extreme, according to research published Monday. Now, two scientists are proposing a new classification that they say an increasing number of storms actually merit: Category 6.
“Climate change has made the strongest storms stronger,” said Michael Weiner, a senior scientist at Lawrence Berkeley National Laboratory. “Introducing this virtual Category 6 would raise awareness of this.”
Weiner and James Kossin, distinguished science advisor at the First Street Foundation, point out that a Category 6 designation could go to any tropical cyclone with sustained winds of at least 192 mph — an intensity that has been exceeded by five storms since 2013.
Meteorologists have debated for years whether the current hurricane scale adequately captures current storm risk — it only takes into account winds, not strong waves or flooding — and whether a new, higher-level category is needed. With the new research, scientists say they are formalizing this discussion, hoping to stimulate more academic debate about the ways in which climate change is increasing the risks of weather as we know it.
“Having a ‘Category 5’ meaning anything above a certain threshold is becoming increasingly problematic,” Kosin said. “He tends to underestimate the risks.”
There’s no indication that government hurricane forecasters will revise their rating scale any time soon — and some meteorologists disagree on whether it should be adopted. However, the proposal highlights how dramatically the potential for severe storms has risen.
As global temperatures rise, the warming of the oceans and atmosphere often creates an environment for storms to grow rapidly and eddy more powerfully than ever before.
Scientists expect this trend will only accelerate in warm basins like the Gulf of Mexico, where some sea surface temperature readings exceeded 100 degrees amid record high global temperatures last summer. Scientists predict that the threat will worsen when the planet’s average temperatures reach 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels. In this scenario, they say the risk of Category 6 storms in the Gulf would double.
Climate change is causing hurricanes to intensify
The research adds to a growing body of understanding — and evidence — that global warming translates into stronger storms.
After all, warm air holds more moisture. More heat means more energy for storms to feed on and unleash violence. Tropical cyclones effectively settle clashes between high and low pressure and hot and cold temperatures, bringing the meteorological environment back into balance.
Global warming has already translated into increased odds of major hurricanes around the world, according to research led by Kosen and published in the Proceedings of the National Academy of Sciences in 2020. Other studies have found that as temperatures rise, more hurricanes experience what meteorologists do. This calls for rapid intensification, and they are doing so at accelerating rates.
Kosin Wonner’s latest paper adds further detail and scientific rigor to our understanding of what climate change means for more intense hurricanes.
They examined observations of past storms to find that five of them were outliers relative to previous Category 5 storms: Typhoon Haiyan in 2013, Typhoon Patricia in 2015, Typhoon Meranti in 2016, Typhoon Goni in 2020, and Typhoon Surigai in 2021.
Typhoon Haiyan killed thousands across the Philippines, stunning meteorologists with its record intensity. Two years later, Patricia became stronger, with maximum sustained winds of 215 mph, although it weakened before making landfall in Mexico.
They analyzed how often conditions might be ripe for such severe storms to develop. They found that near the Philippines, the risk of a Category 6 storm would rise by 50 percent once global warming reaches 2 degrees Celsius above pre-industrial levels, and would double at 4 degrees Celsius. In the Gulf region, risks will triple if temperatures reach 4 degrees above pre-industrial levels.
They used climate models to predict how often Category 6 storms might form in the future and to confirm that this trend is related to climate change and not natural fluctuations. They found that the annual chances of Class VI forming somewhere on the planet would rise to 2% for a 1.5 degree warming, 7% for a 2 degree warming, and 10% for a 3 degree warming.
Some worry that a new category might backfire
Although there may be a scientific basis for the idea of a Category 6 storm, meteorologists would not support its adoption. After all, a Category 5 storm causes “catastrophic” damage that could make the area “uninhabitable for weeks or months,” according to the National Hurricane Center’s description.
“It’s hard for me to imagine needing to move a threat beyond that, even if a hypothetical tropical cyclone had peak winds that would constitute a Category 6 (however you define that),” said Michael Fisher, an associate scientist at NOAA. The National Oceanic and Atmospheric Administration’s (NOAA) Atlantic and Oceanographic Survey. The meteorological laboratory said in an email.
He added that there was a risk that the Category 6 designation would backfire.
“If Category 6 is designated, will that reduce the risk of a Category 5 hurricane, since that is no longer the most dangerous classification?” Fisher added.
Even without the introduction of Category 6, the Saffir-Simpson scale is already facing criticism because it only takes into account wind speed and not risks from storms, floods or hurricanes. To qualify as hurricanes, tropical cyclones must have sustained winds of at least 74 mph; “Major” hurricanes have winds of at least 111 mph.
The National Hurricane Center will soon test a new version of its widely used forecast cone that aims to communicate the risk of a storm’s winds extending far beyond where its eye is expected to reach.
But NOAA research shows that such water-related hazards are the most dangerous hurricane threats, said Deirdre Byrne, a NOAA oceanographer who studies ocean heat and its role in intensifying hurricanes. Although adding a Category 6 “does not seem inappropriate,” combining the Saffir-Simpson scale with a rating like A to E for flood threats could have a greater impact, she said.
“This could save more lives,” Byrne said.
In a statement, National Hurricane Center Director Michael Brennan supported these concerns. He said forecasters at the National Oceanic and Atmospheric Administration “have tried to shift the focus toward individual risks,” including storms, heavy rains and dangerous rip currents, rather than overemphasizing the category of storms and therefore wind threats alone.
“It is not clear that another category will be needed even if storms become stronger,” he said.
Bringing the Saffir-Simpson scale into the future
Kosen and Winer said their research does not mean referring to the sixth category He should Added to the Saffir Simpson scale. They said this decision requires social science research into how it affects people’s risk perceptions and their actions to prepare for tropical cyclones.
Instead, they said their goal is to communicate how dramatically global warming has changed the ecology of hurricanes. Scientists said they hope the discussion will raise the urgent need to better equip coastal communities to confront new and changing extreme weather events.
Weiner compared this to the time when Australians had to add new color to heat maps amid unprecedented heat waves, or when extreme ocean temperatures last month prompted the National Oceanic and Atmospheric Administration (NOAA) to do so. Adding three categories to the coral bleaching alert system.
“The ways we looked at things in the past are not necessarily a good description of the present, and certainly of the future,” he said.