Hurricanes in the Atlantic Ocean are now twice as likely to grow from a weak storm into a major Category 3 or higher hurricane within just 24 hours, according to a study published Thursday.

“These findings should serve as an urgent warning,” said Andra Garner, an assistant professor of environmental science at Rowan University and the author of the new paper.

Many of the costliest climate-related disasters to strike the United States in recent years have been hurricanes that intensified unusually quickly. Hurricane Maria, which killed more than 3,000 people in Puerto Rico and neighboring islands in 2017, strengthened from a Category 1 to Category 5 hurricane in less than 24 hours before making landfall.

When hurricanes intensify so quickly, it becomes more difficult to forecast how severely places will be affected. In the worst cases, officials may be left without time to order evacuations.

From 2001 to 2020, Dr. Garner found that tropical cyclones in the Atlantic Ocean had an 8 percent chance of strengthening from a Category 1 or lower storm into a Category 3 or higher hurricane within 24 hours. By comparison, from 1970 to 1990, similar storms had only a 3 percent chance of strengthening so much, so rapidly.

Hurricane categories, which range from 1 to 5, are determined by the storms’ wind speed. All are dangerous, but storms rated Category 3 and above — with wind speeds over 110 miles per hour — are considered “major” hurricanes.

Tropical storms form when warm ocean water evaporates into the atmosphere. The storms gather their wind power in large part from the difference in temperature between the surface of the ocean and the cooler upper atmosphere. That’s why the North Atlantic hurricane season runs from June through November: It’s the time of year when the water is warmest.

And ocean temperatures are rising.

Globally, oceans have absorbed more than 90 percent of the extra heat trapped on the planet’s surface by greenhouse gas emissions. Since 1850, the global average sea surface temperature has risen by about 0.9 degrees Celsius.

“Without limiting future warming, this is a trend that we could expect to continue to get more extreme,” Dr. Garner said.

Dr. Garner examined historical data from the National Hurricane Center using a variety of statistical analyses on recorded wind speeds of all tropical cyclones in the Atlantic Ocean between 1970 and 2020. She found consistent increases over time in the likelihood of storms to grow quickly.

She also found smaller regional differences within the Atlantic Ocean. There was more rapid intensification of storms along the east coast of the United States, in the southern Caribbean, and in the eastern Atlantic from 2001 to 2020 compared with 1970 to 1990. In the Gulf of Mexico, however, there is less rapid intensification now compared with previous years.

This paper confirms previous studies on hurricane intensity in the Atlantic Ocean. The research is “converging,” said Kerry Emanuel, a professor emeritus of atmospheric science at MIT who conducted early research on this topic, and wasn’t involved in Dr. Garner’s study.

Dr. Emanuel cautioned, however, that climate change from greenhouse gas emissions may not be the only factor contributing to a warmer northern Atlantic and changing hurricane behavior.

Decreased sulfate aerosol pollution following clean-air regulations in the United States and Europe may also affect storms. This type of pollution, a byproduct of burning fossil fuels but distinct from greenhouse gases, reflects sunlight back into the atmosphere and cools the Earth slightly. Dr. Emanuel suggested that more global studies are needed to separate the influence of global climate change from aerosol levels and other local factors specific to the Atlantic.

Even so, “the physics is super clear that as you warm the globe, you raise the thermodynamic potential for hurricanes,” he said.

Dr. Emanuel also emphasized the real-world importance of this research. The rapid intensification of hurricanes is “the forecaster’s nightmare,” he said. “You go to bed, figuratively speaking, at 10 at night, and there’s a tropical storm in the Gulf of Mexico. And you wake up the next morning and it’s a Cat 4, eight hours from landfall. And now you don’t have time to evacuate anybody, to warn them.”

Although this study isn’t global, it’s one of the most robust so far, said Karthik Balaguru, a climate and data scientist at the Pacific Northwest National Laboratory who also studies hurricanes and wasn’t involved in Dr. Garner’s research. The fact that this finding of more quickly growing storms stayed consistent through multiple kinds of statistical analyses shows there’s a real trend in the data, Dr. Balaguru said.

Source link: https://www.nytimes.com/2023/10/19/climate/hurricane-intensity-stronger-faster.html