Study: Global warm­ing to­day mir­rors pre­vi­ous con­di­tions

Texarkana Gazette - - NATION/WORLD - By Evan Bush

More than two-thirds of life on Earth died off some 252 mil­lion years ago, in the largest mass ex­tinc­tion event in Earth’s his­tory.

Re­searchers have long sus­pected that vol­canic erup­tions trig­gered “the Great Dy­ing,” as the end of the Per­mian ge­o­logic pe­riod is some­times called, but ex­actly how so many crea­tures died has been some­thing of a mys­tery.

Now sci­en­tists at the Univer­sity of Wash­ing­ton and Stan­ford be­lieve their mod­els re­veal how so many an­i­mals were killed, and they see fright­en­ing par­al­lels in the path our planet is on to­day.

Mod­els of the ef­fects of vol­canic green­house gas releases showed the Earth warm­ing dra­mat­i­cally and oxy­gen dis­ap­pear­ing from its oceans, leav­ing many ma­rine an­i­mals un­able to breathe, ac­cord­ing to a study pub­lished Thurs­day in the peer-re­viewed jour­nal Sci­ence. By the time tem­per­a­tures peaked, about 80 per­cent of the oceans’ oxy­gen, on av­er­age, had been de­pleted. Most ma­rine an­i­mals went ex­tinct.

The re­searchers tested the model’s re­sults against fos­sil-record pat­terns from the time of the ex­tinc­tion and found they cor­re­lated closely. Al­though other fac­tors, like ocean acid­i­fi­ca­tion, might have con­trib­uted some to the Per­mian ex­tinc­tion, warm­ing and oxy­gen loss ac­count for the pat­tern of the dy­ing, ac­cord­ing to the re­search.

By this cen­tury’s end, if emis­sions con­tinue at their cur­rent pace, hu­mans will have warmed the ocean about 20 per­cent as much as dur­ing the ex­tinc­tion event, the re­searchers say. By 2300, that fig­ure could be as high as 50 per­cent.

“The ul­ti­mate, driv­ing change that led to the mass ex­tinc­tion is the same driv­ing change that hu­mans are do­ing to­day, which is in­ject­ing green­house gases into the at­mos­phere,” said Justin Penn, a UW doc­toral stu­dent in oceanog­ra­phy and the study’s lead au­thor.

Curtis Deutsch, a UW as­so­ciate pro­fes­sor of oceanog­ra­phy and an au­thor of the re­search, said if so­ci­ety con­tin­ues to pump green­house gases at our cur­rent rate, “we have no rea­son to think it wouldn’t cause a sim­i­lar type of ex­tinc­tion.”

The Earth 252 mil­lion years ago was a much dif­fer­ent place. The con­ti­nents as we know them to­day were still mostly one land­mass, named Pangea, which looks like a chunky let­ter “C” on a map.

The cli­mate, how­ever, re­sem­bled Earth’s now, and re­searchers be­lieve an­i­mals would have adapted many traits, like me­tab­o­lism, that were sim­i­lar to crea­tures to­day. Nearly ev­ery part of the Per­mian Ocean, be­fore the ex­tinc­tion, was filled with sea life.

“Less than 1 per­cent of the Per­mian Ocean was a dead zone—quite sim­i­lar to to­day’s ocean,” Deutsch said.

The se­ries of vol­canic events in Siberia that many sci­en­tists be­lieve set off the mass ex­tinc­tion “makes su­per vol­ca­noes look like the head of a pin,” said Seth Burgess, a ge­ol­o­gist and vol­ca­nol­o­gist with the United States Ge­o­log­i­cal Sur­vey.

“We’re talk­ing about enough lava erupted onto the sur­face and in­truded into the crust to cover the area of the United States that if you looked at the U.S. from above was maybe a kilo­me­ter deep in lava,” he said.

Burgess, who has re­searched the Siberian Traps vol­canic events but did not work on the new Sci­ence pa­per, said sci­en­tists be­lieve magma ris­ing from the earth re­leased some ex­tinc­tion-caus­ing green­house gases.

In ad­di­tion, sills of magma still in­side the earth heated mas­sive de­posits of coal, peat and car­bon­ate min­er­als, among oth­ers, which vented even more car­bon and meth­ane into the at­mos­phere.

“That’s how you drive the Per­mian mass ex­tinc­tion, by in­trud­ing mas­sive vol­umes of magma into a basin rich in car­bon-bear­ing sed­i­ments,” he said.

The UW and Stan­ford re­search “takes the next step in fig­ur­ing out why things died at the end of the Per­mian,” Burgess said. “It cou­ples what we think was hap­pen­ing in the cli­mate with the fos­sil record, and it does it el­e­gantly.”

It took a su­per­com­puter more than six months to sim­u­late all the changes the vol­canic erup­tions are sus­pected of caus­ing dur­ing the Per­mian pe­riod. The com­puter mod­els go into re­mark­able de­tail— sim­u­lat­ing things like clouds, ocean cur­rents and ma­rine plant life—in de­scrib­ing what tem­per­a­tures and con­di­tions were like on Earth.

The re­searchers knew that sur­face tem­per­a­tures rose about 10 de­grees Cel­sius in the trop­ics be­cause of pre­vi­ous sci­en­tific anal­y­sis of the fos­silized teeth of eel-like crea­tures called con­odonts.

To run their model, re­searchers pumped vol­canic green­house gases into their sim­u­la­tion to match tem­per­a­ture con­di­tions at the end of the Per­mian pe­riod.

As tem­per­a­tures climbed to­ward the 10-de­gree mark, the model’s oceans be­came de­pleted of oxy­gen, a trend sci­en­tists are eval­u­at­ing in to­day’s oceans, too.

To mea­sure how ris­ing tem­per­a­tures and less oxy­gen would af­fect an­i­mal species of the Per­mian pe­riod, the re­searchers used 61 mod­ern crea­tures—crus­taceans, fish, shell­fish, co­rals and sharks. The re­searchers be­lieve these an­i­mals would have sim­i­lar tem­per­a­ture and oxy­gen sen­si­tiv­i­ties to Per­mian species be­cause the an­i­mals adapted to live in sim­i­lar cli­mates.

Warm­ing’s ef­fects were twofold on the crea­tures, the re­searchers found. In warmer wa­ters, an­i­mals need more oxy­gen to per­form bod­ily func­tions. But warm wa­ters can’t con­tain as much dis­solved oxy­gen, which means less was avail­able to them.

In other words, as an­i­mals’ bod­ies de­manded more oxy­gen, the ocean’s sup­ply dropped.

In their model, the re­searchers were able to quan­tify the loss of habi­tat as species faced in­creas­ingly chal­leng­ing ocean con­di­tions. Sur­face tem­per­a­ture rise and oxy­gen loss were more sub­stan­tial in ar­eas far­ther from the equa­tor. Ex­tinc­tion rates also in­creased at higher lat­i­tudes.

An­i­mals in the trop­ics were al­ready ac­cus­tomed to warmer tem­per­a­tures and lower oxy­gen lev­els be­fore the vol­canic erup­tions shifted the cli­mate, ac­cord­ing to the re­search. As the world warmed, they could move along with their habi­tat.

Ma­rine crea­tures that fa­vored cold wa­ters and high oxy­gen lev­els fared worse: They had nowhere to go.

“The high lat­i­tudes where it’s cold and oxy­gen is high— if you’re an or­gan­ism that needs those kind of con­di­tions to sur­vive, those con­di­tions com­pletely dis­ap­pear from Earth,” Deutsch said.

In mod­ern oceans, warm­ing and oxy­gen loss have also been more pro­nounced near the poles, re­searchers said, draw­ing an­other ana­logue be­tween the shift in cli­mate some 252 mil­lion years ago and what’s hap­pen­ing to­day.

“The study tells us what’s at the end of the road if we let cli­mate (change) keep go­ing. The fur­ther we go, the more species we’re likely to lose,” Deutsch said. “That’s fright­en­ing. The loss of species is ir­re­versible.”

Jill Schensul/The Record/TNS

■ Ac­cord­ing to re­cent re­search from a global col­lab­o­ra­tion of sci­en­tists, the Antarc­tic ice sheet has tripled its rate of ice loss over the last 25 years.

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