The rapid intensification of Hurricane Ian signals the impact of climate change

As Hurricane Ian made its way to Florida this week, it did what six other storms did in the past six years as they approached the United States: it escalated, rapidly.

Some factors help explain the change, including warming waters – fueled by climate change – which give hurricanes more energy to release through the crushing winds and pounding waves. Climate scientists suspect that the slow motion of storms like Ian also stems from global warming, giving them a greater opportunity to strengthen and destroy as long as daily conditions remain mature.

Since 2017, an unprecedented number of Category 4 or higher storms have hit the coast of the United States: Harvey, Irma, Maria, Michael, Laura, Ida and now Ian. They all qualify as “rapid escalation events,” when the wind speed of a storm increases by at least 35 mph within 24 hours.

These types of storms have increased in number over the past few decades. Sixteen of the last 20 hurricanes in the Atlantic basin have experienced rapid intensification.

“Especially in the region near the coast where the hurricane is just before landing, what we are seeing is that hurricane intensification rates have increased,” said Karthik Balaguru, a climate scientist at Pacific Northwest National Laboratory. “And that’s a little disconcerting.”

Ian was just the latest case in which its winds nearly doubled in a 24-hour period, going from a low-end hurricane with sustained winds on Monday at 75 mph to a Category 3 storm with winds of 125 mph on Tuesday. Then, as it approached Florida on Wednesday, its winds increased even faster, going from 120 mph around 2:00 am to 155 mph by 7:00 am.

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The string of intense hurricanes that have hit the United States since 2017 is “one of the busiest times for powerful hurricane landing that we have seen historically,” said Phil Klotzbach, senior researcher at Colorado State University. A comparable period of hurricane activity spanned from 1945 to 1950, when five Category 4 hurricanes hit Florida in six years, making Klotzbach reluctant to call the string of intense storms since 2017 unprecedented.

And, added Klotzbach, a period of rapid strengthening is almost a prerequisite for a storm to become one of the most powerful hurricanes. “The stronger the storm, the more likely it is to intensify rapidly,” he said.

Even so, recent research suggests that the increase in rapidly intensifying storms is having a profound impact.

A study published earlier this year found that since 1990 a steadily increasing number of global tropical cyclones have undergone what the study termed “extremely rapid intensification,” with winds increasing at least 50 knots, or 57 mph. , in a period of 24 hours. Another 2018 study focusing on the Atlantic Basin found that among cyclones that strengthened fastest, their intensification rates have increased, growing by 4 mph every decade for the past 30 years.

The most recent assessment by the Intergovernmental Panel on Climate Change came to a similar conclusion, noting that tropical cyclones are likely to become more intense and subject to rapid intensification.

“I would say that one of the most troubling things about climate change is a change in extremes,” Balaguru said. “Rapid escalation is a process that fits that category of extremes.”

For example, Balaguru said, if a storm in the Caribbean Sea four decades ago intensified by 34 mph in one day, the same storm would increase by 48 mph in today’s climate.

And a preliminary analysis of Ian’s precipitation released Thursday by Kevin Reed, professor at Stony Brook University and Michael Wehner, senior scientist at Lawrence Berkeley National Laboratory, based on previously peer-reviewed research, found that climate change is responsible for the 10% increase in precipitation rates. extreme of Ian.

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A warmer ocean, coupled with low vertical wind shear, helped drive the rapid intensification of recent storms.

In general, ocean waters must be above 79 degrees Fahrenheit for a hurricane to develop and persist. Over the past few decades, the ocean has warmed at record speeds due to human-emitted greenhouse gases, making it easier to reach this threshold. As Ian was moving away from Cuba, sea surface temperatures were approaching 86 degrees.

The rise in global air temperature also means that waters, especially in bodies like the bathub-style Gulf of Mexico, are warming beyond their surface. The deeper the heat goes, the more fuel can flow into a slow moving storm like Ian. Warm seawater evaporates and pumps moisture into the air, which can condense in storms, clouds, and rain.

“A storm can stay on this warm water for almost days, and if it’s deep enough, it won’t kill itself,” said James Kossin, senior scientist at the Climate Service, risk assessment consultant and former scientist at the National Oceanic. and Atmosphere Administration which conducted hurricane intensification studies.

Vertical wind shear, which changes wind speed and direction at different altitudes during a storm, also has a key influence on hurricane intensity, although researchers are still deciphering any long-term trends. Strong wind shear can weaken a hurricane, while weaker shear can help a hurricane form and strengthen.

Wind shear has been relatively low in the western Atlantic since 2017, a factor that has since contributed to the flurry of tropical cyclones, according to Klotzbach. It is possible that, in the long term, climate change may make this environmental condition more common. Scientists speculate that the jet stream, which creates strong wind shear, could be pushed north as global temperatures rise.

Climate change could also increase the potential for hurricanes to intensify and destroy, slowing them down, increasing the duration of damaging winds and rain floods.

For example, while Hurricane Ian took a similar path and with a similar intensity as Hurricane Charley in 2004, Charley exploded in Florida at 20 mph, while Ian moved only half the speed. This allowed Ian to dump up to 20 inches of rain along his path, already more than double Charley’s rainfall, according to initial estimates.

Scientists speculate that the slow-moving storms may result from rapid warming at the Earth’s poles, because this has narrowed the temperature and pressure gap from the poles to lower latitudes. These differences drive winds around the world, pushing around weather systems, including hurricanes, like corks in a stream. So when they are minimized, this could cause a wider slowdown in global weather systems.

The same phenomenon could cause abnormal waves of extreme heat and bursts of polar frost, because the jet stream winds that normally disrupt weather patterns and drive storm systems are weaker.

“It appears that the whole atmosphere is getting slower and, as a result, the storms carried within it are moving more slowly,” said Kossin.

Slower storms are capable of dropping huge amounts of rain. Hurricane Harvey rained more than 60 inches of rain in parts of southeastern Texas because it froze over the region for nearly two days.

Likewise, if a storm with hurricane winds stays in one spot long enough, “it will eventually flatten everything,” Kossin said.

Authorities have changed the way they make forecasts and warn the public, meteorologists said. due to the danger posed by the sudden escalation of a storm.

The National Hurricane Center has reported fears of a rapid escalation with Ian as the storm turned into a tropical storm. On Friday morning, well before Ian approached the Cayman Islands and Cuba, forecasters warned that it would likely feed from the warm waters of the Gulf of Mexico and become a major hurricane approaching Florida within five days.

“We have much better tools to be able to predict this rapid intensification than before,” said Klotzbach. “The models are just better.”

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