‘HIGHLY UN­USUAL’

Study: Cli­mate change al­ready mak­ing hur­ri­canes more fierce

The Times-Tribune - - HEALTH&SCIENCE - BY JENNY STALE­TOVICH

MI­AMI — Cli­mate change has al­ready made At­lantic hur­ri­canes more fierce, driv­ing up the num­ber of storms that rapidly in­ten­sify, be­come more lethal and dif­fi­cult to fore­cast, ac­cord­ing to new re­search led by the Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion.

Pub­lished Thurs­day in the jour­nal Na­ture, the re­search looked at storms churn­ing in the At­lantic over nearly three decades be­tween the 1980s and 2000s and found the num­ber of storms that un­der­went rapid in­ten­si­fi­ca­tion nearly tripled. The team con­sid­ered nat­u­ral vari­a­tions in cli­mate that might drive the in­crease but still found the num­ber “highly un­usual.”

While past stud­ies have con­firmed a rise in more in­tense storms and pre­dicted they would con­tinue to in­crease as a warm­ing planet heats up oceans, this is the first to di­rectly link the cause to cli­mate change. And to show such a dra­matic in­crease.

“I wasn’t sur­prised there was an up­ward trend, but I was sur­prised by the mag­ni­tude,” said lead au­thor Kier­nan Bha­tia, who earned a doc­toral de­gree from the Uni­ver­sity of Mi­ami and com­pleted the re­search while a fel­low at Prince­ton Uni­ver­sity work­ing with the NOAA team.

Search for con­sis­tency

For the study, re­searchers looked at the record of hur­ri­canes in the At­lantic. Global data ex­ist, but they said they had less con­fi­dence in the in­for­ma­tion be­cause of track­ing meth­ods and sig­nals that might change find­ings. As re­port­ing and satel­lites have im­proved, re­searchers say that has in­flu­enced the record of storms and ap­peared to in­di­cate an in­crease. So they look for con­sis­tency in data. The pe­riod be­tween 1982 and 2009 re­mained re­mark­ably con­sis­tent for both satel­lite and hur­ri­cane in­for­ma­tion.

Once they had the data, they also looked for nat­u­ral vari­abil­ity in cli­mate that might fuel rapid in­ten­si­fi­ca­tion. Rapid in­ten­si­fi­ca­tion oc­curs when wind speeds spike, in­creas­ing by about 35 mph in less than 24 hours. Such storms are un­pre­dictable, even more dif­fi­cult to fore­cast in in­ten­sity, and tend to cause the most dam­age.

Last Oc­to­ber, Hur­ri­cane Michael trans­formed from a mid­dling trop­i­cal storm with 40 mph winds to a Cat­e­gory 1 hur­ri­cane in less than a day. It un­der­went two more rapid changes be­fore it made land­fall as a fe­ro­cious storm with 155 mph winds, just shy of a Cat­e­gory 5, in the Pan­han­dle. A month ear­lier, Florence rapidly in­ten­si­fied be­fore slam­ming the Carolina coast. Those storms were not in­cluded in the study. How­ever, it did cover the record-break­ing 2005 sea­son, which pro­duced 28 named storms in­clud­ing Ka­t­rina and Wilma, as well as 1992’s lethal Hur­ri­cane An­drew.

Fo­cus­ing on a cul­prit

Nat­u­ral changes can fuel more in­tense storms. For ex­am­ple, since the 1990s, a pat­tern that can last decades and af­fect tem­per­a­tures on the sur­face of the ocean has been run­ning warm. El Niños and La Niñas, other pat­terns that change ocean tem­per­a­tures year to year in the Pa­cific, can also trig­ger more hur­ri­canes in the At­lantic. But those fluc­tu­a­tions failed to ac­count for the steep in­crease, Bha­tia said, which left man-made changes on the planet as the cul­prit.

Ris­ing ocean tem­per­a­ture has been con­sid­ered a chief cause, but Bha­tia said sci­en­tists have so far not con­firmed it’s the only fac­tor.

“It’s def­i­nitely some­thing we’re try­ing to un­der­stand bet­ter,” he said. “If you think of rapid in­ten­si­fi­ca­tion as a recipe, we know warm ocean wa­ters are part of the in­gre­di­ents, but we still haven’t iden­ti­fied the most im­por­tant in­gre­di­ents. It’s re­ally hard to make good cook­ies with­out su­gar. That’s the ocean part. But at the same time you need flour and bak­ing soda.”

AS­SO­CI­ATED PRESS FILE

A res­i­dent walks past the shat­tered win­dow of a room at a dam­aged mo­tel Oct. 16 in Panama City, Fla., where guests con­tin­ued to stay in the af­ter­math of Hur­ri­cane Michael.

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