Earth has sur­vived warm­ing be­fore. But life al­most didn’t make it through

New sim­u­la­tion shows how cli­mate change can cause a mass ex­tinc­tion

Toronto Star - - NEWS - CARL ZIM­MER THE NEW YORK TIMES

About 252 mil­lion years ago, Earth al­most died.

In the oceans, 96 per cent of all species be­came ex­tinct. It’s harder to de­ter­mine how many ter­res­trial species van­ished, but the loss was com­pa­ra­ble.

This mass ex­tinc­tion, at the end of the Per­mian Pe­riod, was the worst in the planet’s his­tory, and it hap­pened over a few thou­sand years at most — the blink of a ge­o­log­i­cal eye.

On Thurs­day, a team of sci­en­tists of­fered a de­tailed ac­count­ing of how ma­rine life was wiped out dur­ing the Per­mi­anTri­as­sic mass ex­tinc­tion. Global warm­ing robbed the oceans of oxy­gen, they say, putting many species un­der so much stress that they died off.

And we may be re­peat­ing the process, the sci­en­tists warn. If so, then cli­mate change is “solidly in the cat­e­gory of a cat­a­strophic ex­tinc­tion event,” said Curtis Deutsch, an earth sci­en­tist at the Univer­sity of Wash­ing­ton and co-au­thor of the new study, pub­lished in the jour­nal Sci­ence.

Re­searchers have long known the gen­eral out­lines of Per­mian-Tri­as­sic cat­a­clysm. Just be­fore the ex­tinc­tions, vol­ca­noes in what is now Siberia erupted on a tremen­dous scale. The magma and lava that they belched forth pro­duced huge amounts of car­bon diox­ide.

Once in the at­mos­phere, the gas trapped heat. Re­searchers es­ti­mate that the sur­face of the ocean warmed by about 10 C. Some re­searchers ar­gue that the heat alone killed off many species. Oth­ers be­lieve that the warmth re­duced oxy­gen in the ocean, as­phyx­i­at­ing the species liv­ing there. Rocks from the mass ex­tinc­tion ap­pear to have formed when at least some of the ocean was lack­ing oxy­gen.

Dr. Deutsch and Justin Penn, a grad­u­ate stu­dent, recre­ated the world at the end of the Per­mian Pe­riod with a largescale com­puter sim­u­la­tion, com­plete with a heat-trap­ping at­mos­phere and a cir­cu­lat­ing ocean.

As the Siberian vol­ca­noes flooded the vir­tual at­mos­phere with car­bon diox­ide, the at­mos­phere warmed. The ocean warmed, too — and ac­cord­ing to the model, it be­gan los­ing oxy­gen.

Some parts lost more than oth­ers. On the sur­face, for ex­am­ple, fresh oxy­gen was pro­duced by pho­to­syn­thetic al­gae. But as the ocean warmed, its cir­cu­la­tory cur­rents also slowed, the model demon­strated.

Oxy­gen-poor wa­ter set­tled to the bot­tom of the oceans and be­fore long, the deep was gasp­ing. Ris­ing tem­per­a­tures and plung­ing oxy­gen must have made huge swaths of the oceans un­in­hab­it­able. Some species sur­vived here and there. But most dis­ap­peared com­pletely.

“Ev­ery­thing was los­ing a lot of habi­tat, cre­at­ing the risk of ex­tinc­tion,” said Dr. Deutsch. “But the risk was ac­tu­ally higher in places that were cold. That was a bit sur­pris­ing.”

You might ex­pect that an­i­mals near the Equa­tor would be at a greater risk, be­cause the wa­ter was warm to be­gin with. But Dr. Deutsch’s model sug­gested a very dif­fer­ent kind of apoca­lypse.

An­i­mals in oxy­gen-rich cold wa­ter could not han­dle the sud­den drop, while those in trop­i­cal wa­ters were al­ready adapted to poor oxy­gen. And the cold-wa­ter species could not find refuge else­where.

The new study of­fers an im­por­tant warn­ing to hu­mans over the next few cen­turies.

“The way the Earth sys­tem is re­spond­ing now to the buildup of CO2 is in the ex­act same way that we’ve seen it re­spond in the past,” said Dr. Kump.

“Left unchecked, cli­mate warm­ing is putting our fu­ture on the same scale as some of the worst events in ge­o­log­i­cal his­tory,” Dr. Deutsch said.

JILL SCHENSUL TRI­BUNE NEWS SER­VICE

About 252 mil­lion years ago, an­i­mals in oxy­gen-rich cold wa­ter could not han­dle the sud­den tem­per­a­ture jump of about 10 C.

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