A Jurassic wake-up call

About 183 million years ago -- during the Toarcian Age, one of the subdivisions of the early Jurassic Period -- there was a sudden and puzzling extinction.

Things had been recovering nicely after the End-Triassic Mass Extinction, eighteen million years earlier.  While dinosaurs were not yet at the peak they would hit in the later Jurassic, they were well on their way to taking over the place.  The temperatures were cool -- there's evidence of widespread glaciation during the ten million years prior -- but by and large, everything seemed to be coping just fine.

Then, suddenly, wipeout.

It wasn't as big as some of the truly dramatic mass extinctions the Earth has experienced, but that doesn't mean it was insignificant.  Marine invertebrates got clobbered, dropping both in diversity and in overall numbers.  Over ninety percent of coral species went extinct.  Two entire orders of brachiopods died; bivalves, ostracods, and ammonoids survived, but with greatly reduced populations.  Coelophysid and dilophosaurid dinosaurs got wiped out completely.  Seed ferns and lycophytes declined sharply, to be replaced by cycads and conifers.

Fossil seed fern [Image is in the Public Domain]

All of it occurred rapidly -- the current estimates are less than five hundred thousand years, which is a snap of the fingers geologically.

So what happened?

The culprit seems to have been the Karoo-Ferrar Large Igneous Province, an enormous volcanic formation (estimated at about three million square kilometers) now underlying much of southern Africa, eastern Antarctica, and southwestern South America.  At this point, Gondwana -- the southern half of the supercontinent of Pangaea -- had just begun to break up, and this massive series of eruptions was part of the process of rifting.  But what caused the extinction was not the eruption itself -- it was the sudden spike of atmospheric carbon dioxide, which swung the climate from a glacial period to a hothouse.  A study released last week by a team at Duke University found evidence of a twenty thousand gigaton carbon dioxide pulse, triggering not only a drastic temperature increase, but widespread ocean acidification and anoxia.

According to the study, during the event, eight percent of the global seafloor -- an area three times that of the United States -- became completely anoxic.  The pH dropped so much that animals with calcium carbonate exoskeletons literally dissolved.  Rainfall patterns shifted dramatically, impacting terrestrial biomes as well.  By the time things began to recover, it was a changed world, all in a matter of a half of a million years.

Ready for the punchline? 

Today's rate of carbon dioxide increase in the atmosphere is over two hundred times what it was during the Toarcian Extinction Event.

Twenty thousand gigatons in five hundred thousand years is a lot, and had a devastating effect on the world's ecosystems; we've put two thousand gigatons into the atmosphere in the past two hundred years.  

Is it any surprise why the scientists have been trying like hell to get everyone's attention?

"We just don't have anything this severe [in the geological record]," said paleoclimatologist Michael Kipp, who co-authored the study.  "We go to the most rapid CO2-emitting events we can in history, and they're still not rapid enough to be a perfect comparison to what we're going through today. We're perturbing the system faster than ever before.  We have at least quantified the marine oxygen loss during this event, which will help constrain our predictions of what will happen in the future."

None of this is meant to stun people into giving up.  We have got to get a handle on this.  Yes, we've crossed several benchmarks the climate scientists have warned us about.  But every tenth of a degree's further increase we can prevent will mitigate the effects of what we're doing.  We have got to stop electing politicians who shrug their shoulders about anthropogenic climate change, most strikingly Florida's belligerent and willfully stupid Governor Ron DeSantis, who recently signed a law striking any mention of climate change in state statutes, banning offshore wind turbines, and deregulating natural gas production, transport, and use.  

In one of the lowest-lying, most hurricane-prone states in the country.

Maybe it will take our getting slapped hard to wake us up; we don't have a good record of addressing problems that aren't right in front of our faces.  Events like the massive heat dome that just cooked the southern, central, and northeastern states are just the beginning, and are easily forgotten once they pass.  They're predicting a vicious hurricane season, fueled by a central Atlantic with a surface the temperature of bath water, but we've seen dire predictions before and gone on our way as if nothing was amiss.

So how many lives will it cost before that wake-up call is finally listened to?

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