University of Southern California and 17 others surveyed 300 million years of ocean life
The breadth of this study – 18 research institutions and 21 scientists worldwide — and the examination of hundreds of studies stretching so far back into the geologic record makes this conclusion a singularly solid statement about the present trend.
“From everything we know today, it looks like the current rate of carbon dioxide (CO2) emissions” may spell the loss of “organisms we care about — coral reefs, oysters, salmon,” says Bärbel Hönisch, the study’s lead author, who I reached by phone in New York. She’s a paleo-oceanographer at Columbia University’s Lamont-Doherty Earth Observatory. The paper’s being published today in the journal Science.
The danger comes from what happens when CO2 is absorbed by the oceans: CO2 and water create carbonic acid, the stuff that makes soft drinks bubbly. It also makes the oceans more acidic. That acid can dissolve the shells of “keystone” species that are the building blocks for marine life. The world’s oceans are already twice as acidic – a pH drop from 8.2 to 8.1 — as they were at the start of the Industrial Revolution. That’s an acidification rate 10 times faster than anything found in the record over the past 300 million years, according to this new survey.
For her part in the study, USC doctoral candidate Rowan Martindale was looking at the juncture between the Triassic and Jurassic eras, 200 million years ago. It was a cataclysmic time when the earth’s continents were splitting apart, huge strings of volcanoes were erupting, atmospheric CO2 was at one of the highest levels ever and — you guessed it — hardly any evidence of limestone or coral, two things that dissolve in acidic water. It marked one of the five biggest extinction events in the planet’s history. Atmospheric carbon was increasing at the rate of one gigaton – about 2.2 trillion pounds — per year.
Today, atmospheric carbon is increasing at the rate of eight gigatonnes per year — about 17.6 trillion pounds. ‘Something weird was going on in the ocean back then,” Martindale says. “The modern ocean chemistry is changing, and nobody really knows exactly what’s going happen.”
Hönisch says the team cited hundreds of studies — the journal had to put a limit on their end list of 218 items — and looked at many more over the past year-and-a-half. “The strength is that when we compare these different events [in the geologic record], we can see the similarities. We can also see where we need more information.”
Both Honisch and Martindale will tell you the paleo record has its gaps and intriguing questions for further study — exactly how atmospheric warming interacts with ocean acidity, and key ocean sediments they’d love to sample that have disappeared back below the sea floor, for example — but their conclusion is clear: the world’s oceans are acidifying at a rate that has never been seen before.
“Maybe things are not as bad as we think, but we don’t know, says Hönisch. “[And] by the time we do, it may be too late to turn around.”