A group of top hurricane experts, including several federal researchers at the National Oceanic and Atmospheric Administration, published striking new research Thursday, suggesting that hurricanes in the Atlantic Ocean have grown considerably worse and that climate change is part of the reason why.\
The study focused on rapid intensification, in which hurricanes may grow from a weak tropical storm or Category 1 status to Category 4 or 5 in a brief period. They found that the trend has been seen repeatedly in the Atlantic in recent years. It happened before Hurricane Harvey struck Texas and before Hurricane Michael pummeled the Gulf Coast with little warning last fall. Hurricane Michael, for example, transformed from a Category 1 into a raging Category 4 in the span of 24 hours.
The study, published in Nature Communications, describes its conclusion in blunt language, saying the Atlantic already has seen “highly unusual” changes in rapid hurricane intensification, compared to what models would predict from natural swings in the climate. That led researchers to conclude that climate change played a significant role.
“Natural variability cannot explain the magnitude of the observed upward trend,” they wrote. The research was led by Kieran Bhatia, who conducted the research as a graduate researcher at Princeton University and NOAA’s Geophysical Fluid Dynamics Laboratory.
“There’s just a whole host of issues that come along with rapid intensification, and none of them are good,” said Jim Kossin, one of the study’s authors and a hurricane expert with the National Oceanic and Atmospheric Administration.
The increase in prevalence of rapidly intensifying storms, Kossin said, means both that there are more strong storms overall and that there are more risky situations near land.
“Rapid intensification is exceedingly dangerous because people, they’re not warned adequately, they’re not prepared, many of them don’t evacuate,” he said.
The findings come in the wake of two of the most damaging years for hurricanes and other extreme events. In 2017, according to NOAA figures, the United States saw $306 billion in disaster losses, largely driven by Hurricanes Harvey, Maria and Irma. In 2018, Hurricanes Florence and Michael were major factors in a $91 billion damage total.
Rapid intensification is generally measured by comparing the strength of a hurricane over a 24-hour period. A change in storm wind speed of greater than 35 mph in 24 hours is generally the cutoff.
In the new study, the researchers used two separate data sets of storm behavior to analyze changes in the tendency of hurricanes to rapidly intensify. They looked at the globe and also at the Atlantic region specifically, but had less confidence in global figures, given that record-keeping of storm behavior is less reliable in other regions than in the carefully studied Atlantic.
Over a 28-year period, from 1982 to 2009, the percentage of Atlantic storms that rapidly intensified had tripled, the study found.
This was true of both data sets used, one of which records official hurricane statistics from global monitoring agencies, such as the National Hurricane Center, and one of which uses satellite imagery to estimate storm strengths.
The researchers then used a model that can reliably simulate hurricanes to determine whether the rates of rapid intensification found in the study are significantly greater than seen in a version of the model that did not include human-caused climate change.
One obvious inference is that warmer ocean temperatures, which provide the fuel for hurricanes, are probably driving explosive storm strengthening.
Kossin said that if hurricanes have the potential to achieve higher intensities because of warmer ocean conditions, they’ll also probably rapidly intensify more frequently, since they have more “headroom” to grow in strength. That could explain the results.
And Kossin noted that the study only went through 2009, due to limitations in the satellite data set. That means it did not include multiple recent rapidly intensifying storms - if it had, the findings might have been even stronger.
“We’re finding trends even without including what we’ve been seeing in the last few years,” Kossin said.
Still, the study did include some major devastating storms, such as 2005’s Hurricane Wilma, which rapidly intensified from a strong tropical storm into a Category 5 hurricane in 24 hours.
“It is fortunate that this ultrarapid strengthening took place over open waters, apparently void of ships, and not just prior to a landfall,” the National Hurricane Center wrote in a post-season analysis of the storm.
Kerry Emanuel, a hurricane expert at MIT, said the new results make theoretical sense - that storms are intensifying faster as the climate warms. “One theoretical prediction, backed up by modeling results, is that intensity change should increase faster with global warming than intensity itself,” he said by email.
The Washington Post’s Jason Samenow contributed to this report.