A warmer world makes hur­ri­canes wet­ter and more in­tense.

Daily Times (Primos, PA) - - NEWS - By Seth Boren­stein

WASH­ING­TON » A warmer world makes for nas­tier hur­ri­canes. Sci­en­tists say they are wet­ter, pos­sess more en­ergy and in­ten­sify faster.

Their storm surges are more de­struc­tive be­cause cli­mate change has al­ready made the seas rise. And lately, the storms seem to be stalling more of­ten and thus dump­ing more rain.

Study af­ter study shows that cli­mate change in gen­eral makes hur­ri­canes worse. But de­ter­min­ing the role of global warm­ing in a spe­cific storm such as Hur­ri­cane Florence or Typhoon Mangkhut is not so sim­ple — at least not with­out de­tailed sta­tis­ti­cal and com­puter analy­ses.

The As­so­ci­ated Press con­sulted with 17 me­te­o­rol­o­gists and sci­en­tists who study cli­mate change, hur­ri­canes or both. A few ex­perts re­main cau­tious about at­tribut­ing global warm­ing to a sin­gle event, but most of the sci­en­tists clearly see the hand of hu­mans in Florence.

Global warm­ing didn’t cause Florence, they say. But it makes the sys­tem a big­ger dan­ger.

“Florence is yet an­other poster child for the hu­man-su­per­charged storms that are be­com­ing more com­mon and de­struc­tive as the planet warms,” said Jonathan Over­peck, dean of the en­vi­ron­ment school at Uni­ver­sity of Michi­gan. He said the risk ex­tends be­yond the At­lantic Ocean, such as Typhoon Mangkhut, which hit the Philip­pines on Fri­day.

For years, when asked about cli­mate change and spe­cific weather events, sci­en­tists would re­frain from draw­ing clear con­nec­tions. But over the past few years, the new field of at­tri­bu­tion stud­ies has al­lowed re­searchers to use statis­tics and com­puter mod­els to try to cal­cu­late how events would be dif­fer­ent in a world with­out hu­man­caused cli­mate change.

A cou­ple of months af­ter Hur­ri­cane Har­vey, stud­ies found that global warm­ing sig­nif­i­cantly in­creased the odds for Har­vey’s record heavy rains.

“It’s a bit like a plot line out of ‘Back to the Fu­ture,’ where you travel back in time to some al­ter­nate re­al­ity” that is plau­si­ble but with­out hu­mans chang­ing the cli­mate, said Uni­ver­sity of Ex­eter cli­mate sci­en­tist Peter Stott, one of the pi­o­neers of the field.

A Na­tional Academy of Sciences re­port finds these stud­ies gen­er­ally cred­i­ble. One team of sci­en­tists tried to do a sim­i­lar anal­y­sis for Florence, but out­side ex­perts were wary be­cause it was based on fore­casts, not ob­ser­va­tions, and did not use enough com­puter sim­u­la­tions.

As the world warms and science ad­vances, sci­en­tists get more spe­cific, even with­out at­tri­bu­tion stud­ies. They cite ba­sic physics, the most re­cent re­search about storms and past stud­ies and put them to­gether for some­thing like Florence.

“I think we can say that the storm is stronger, wet­ter and more im­pact­ful from a coastal flood­ing stand­point than it would have been BE­CAUSE of hu­man-caused warm­ing,” Pennsylvania State Uni­ver­sity cli­mate sci­en­tist Michael Mann wrote in an email. “And we don’t need an at­tri­bu­tion study to tell us that in my view. We just need the laws of ther­mo­dy­nam­ics.”

Ge­or­gia Tech cli­mate sci­en­tist Kim Cobb looks not just at ba­sic physics but all the peer-re­viewed stud­ies that es­pe­cially link cli­mate change to wet­ter storms.

“We have solid data across decades of rain­fall records to nail the at­tri­bu­tion — cli­mate change is in­creas­ing the fre­quency of ex­treme rain­fall events,” Cobb said.

Sev­eral fac­tors make sci­en­tists more con­fi­dent in point­ing the cli­mat­e­change fin­ger at Florence.

For ev­ery de­gree the air warms, it can hold nearly 4 per­cent more wa­ter (7 per­cent per de­gree Cel­sius) and of­fer mea­sur­ably more en­ergy to goose the storm, sci­en­tists said.

“The amount of wa­ter that comes out of hur­ri­canes is cer­tainly the most ro­bust con­nec­tion that we have,” Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion cli­mate sci­en­tist Jim Kossin said.

And to look at Florence specif­i­cally, “it’s very likely that cli­mate change has warmed the ocean such that the hur­ri­cane’s in­tense rain­fall is more de­struc­tive than with­out global warm­ing,” said Weather Un­der­ground Me­te­o­rol­ogy Di­rec­tor Jeff Mas­ters, a for­mer hur­ri­cane hunter.

The warmer air and wa­ter also makes storms more in­tense or stronger, Stott said.

A Kossin study this year showed that trop­i­cal cy­clones — a cat­e­gory that in­cludes hur­ri­canes and ty­phoons — are mov­ing slower and even stalling. Kossin said “it’s hap­pen­ing a lot more than it used to.” Sev­eral stud­ies agree that cli­mate change is to blame but dif­fer slightly in their con­clu­sions.

With the emer­gence of Florence, some place in the U.S. has been drenched be­cause of a stalled hur­ri­cane for four years in a row, storm surge ex­pert Hal Need­ham said.

Kossin and Over­peck also pointed to stud­ies that show storms are in­ten­si­fy­ing more rapidly than they used to.

Just like in Su­per­storm Sandy, sci­en­tists said it is clear that hur­ri­cane storm surge is wors­ened by sea level rise be­cause the power of 6 to 10 feet of wa­ter comes on top of seas that were con­sid­er­ably lower decades ago. An ex­tra 8 inches or so can mean the dif­fer­ence be­tween stay­ing dry or get­ting dam­aged, Mas­ters said.

In the Caroli­nas, nat­u­ral and tem­po­rary cli­mate fac­tors added to the “march up­wards” from global warn­ing. Be­cause of that, the seas have risen nearly 5 inches in five years, said An­drea Dut­ton of the Uni­ver­sity of Florida.

Me­te­o­rol­o­gist Ryan Maue of weath­er­mod­els. com cau­tioned that ob­servers should “stick to over­all trends around the world and not in­di­vid­ual cases.”

Uni­ver­sity of Mi­ami hur­ri­cane ex­pert Brian McNoldy said there are too many ever-chang­ing fac­tors that make it hard to blame cli­mate change specif­i­cally.

“If you are try­ing to make cli­mate pol­icy,” Maue said Fri­day, “you don’t want to make it on a storm-bystorm ba­sis.”

Fol­low Seth Boren­stein on Twitter: @boren­bears . His work can be found here .

The As­so­ci­ated Press Health & Science Depart­ment re­ceives sup­port from the Howard Hughes Med­i­cal In­sti­tute’s Depart­ment of Science Ed­u­ca­tion. The AP is solely re­spon­si­ble for all content.

For the lat­est on Hur­ri­cane Florence, visit https://www.ap­news.com/tag/Hur­ri­canes .

NOAA VIA AP

This satel­lite im­age pro­vided by NOAA shows Hur­ri­cane Florence on the eastern coast of the United States on Fri­day.

TOM COPELAND - THE AS­SO­CI­ATED PRESS

High winds and wa­ter sur­round build­ings as Hur­ri­cane Florence hits Front Street in down­town Swans­boro, N.C., Fri­day.

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