Category 6? Climate change can lead to a rapid intensification of hurricanes.

In just over a day, Hurricane Florence exploded by jumping from a Grade 1 monastery to a 140 mph wind. This process, which intensifies rapidly, is both extremely dangerous and misunderstood. But new research indicates that as the climate continues to warm up, storms will do so faster and more often and, in extreme cases, will become so powerful that they could be referred to as "category 6".

The new science demonstrates the growing capacity of supercomputing to drive simulations of the planet that show the future of massive features such as the atmosphere and oceans, while retaining enough detail to capture smaller ones like hurricanes. of categories 4 and 5. It is so that a model created at the Geophysical Laboratory of Fluid Dynamics of the National Oceanic and Atmospheric Administration has generated new discoveries and has identified how the rapid intensification of storms could worsen things later in this century.

"The reason there will be more big hurricanes will not necessarily be a lot more storms … it's really the fact that these storms will arrive faster," said Kieran Bhatia, lead author of the new study on the Journal of Climate. Bhatia completed the job while a graduate researcher at Princeton University and the nearby NOAA laboratory.

In recent years, we have already seen signs of intense hurricanes intensifying by intensifying explosively. Hurricane Maria from last year, for example, went from a simple tropical depression to a Category 5 storm in just over two days; or Hurricane Patricia in 2015, whose winds in the eastern Pacific exceeded 210 mph, more than 50 mph as the lowest category 5 storms.

Kerry Emanuel, an expert on hurricanes and climate change at MIT, said in an email that the research "could change the game in climate-hurricane studies". Emanuel was not directly involved in the work.

The study relies on increased computing power to achieve something that until now was very difficult – capturing a reasonable representation of hurricanes in a global climate change model that simulates both the atmosphere and the oceans.

By dividing the globe into squares of about 16 miles over 16 miles, the researchers were able to simulate Category 4 and 5 storms and the locations where they are currently located around the world, which is not the case. perfectly representative.

But when researchers switched from late-20th century hurricane simulation to those of the future as part of an intermediate climate change scenario, they saw big changes. Between 2016 and 2035, there were more hurricanes in general and 11% more hurricanes in categories 3, 4 and 5; at the end of the century, there were 20% more of the worst storms.

In addition, the study found that storms of extreme intensity, with sustained winds of more than 190 mph, were also becoming more frequent. While she found only nine of these storms in a climate simulation of the late 20th century, she found 32 for the period 2016-2035 and 72 for the period 2081-2100.

There is no "category 6" on the Saffir-Simpson scale, but the category 5, which is indefinite, starts at 157 mph, much lower than the intensity of these storms. the wind speed before reaching the next category: for example, the lowest category 5 storm would be 24 mph higher than the lowest category 4.

Recently, scientists have begun to talk about a possible designation of "category 6", although there is considerable debate about whether this is really a good idea. other.

"What you expect if you head for more intense storms is that you will begin to see intensities that you have never seen before," said Gabriel Vecchi, a Princeton atmosphere scientist who was one of the authors of the study.

That said, Vecchi is not sure of the concept of "category 6".

"I think I would bring a social scientist here to see what would be the net worth of a category 6 designation," he said.

What is perhaps most significant, is that new research shows that rapid intensification seems to be the main mechanism that causes stronger storms in a warmer climate. Of course, in the coming years, he found more storms of more than 45mph in 24 hours, as did Hurricane Florence, and even a number of rare and extremely extreme storms that s & rsquo; Climb more than 115 mph in 24 hours.

To understand why rapid intensification is important, one must take into account the global population of tropical cyclones (known as cyclones, typhoons and cyclones, depending on the region). There are many relatively small storms – categories 1 and 2 – but also many dangerous and intense storms with winds exceeding 130 km / h.

The difference between the two groups, according to previous research, is often a difficult process to predict in which the hurricane is rapidly increasing, usually in the presence of very favorable environmental conditions, such as very warm seas at considerable depths, many available resources. humidity in the air and low wind around the storm.

Given that climate change is expected to occur, the warmer weather conditions in the ocean have naturally raised questions. Now, new research has suggested that this will be the case.

Certainly, the prospective study of Bhatia and his colleagues remains agnostic about what is happening right now – a period in which we are already witnessing very strong storms, like Patricia.

"This document does not really say what we have had so far, if there is a trend," said Bhatia. "It says literally," In this particular model, climate change will make XYZ more likely. "

But this model is a major breakthrough, said Emanuel, of MIT, who was not involved in the research but said he was "well informed" of the study.

The resolution of the new computer model is "one of the highest ever achieved" for a global climate model that captures the entire Earth and its atmosphere and oceans, said Emanuel in an email. "It's important to note that this remains under-solved [tropical cyclones]but that's an important step in the right direction. Unlike almost every other [global climate model]technology-based studies, it simulates the Cat 4-5 storm and predicts an increase in overall frequency [tropical cyclones] globally. "

But Chris Landsea, another leading hurricane researcher, who heads the Hurricane Center's National Tropical Weather Analysis and Forecasting Directorate, was less convinced, noting that the expected strong increase in future hurricane strength has been shown. . . no significant change in the major numbers of hurricanes, and only a 2-5% increase in hurricane intensity. "

Scientists have been debating for more than a decade exactly what happens to hurricanes when the climate warms up. no study will change that, as their authors themselves admit.

Meanwhile, as scientists continue their debate, Hurricane Florence should cross the sea one degree or a little more than normal on its way to the east coast.