Ancient global warming ‘no match for human-led emissions’
Image credit: Pablo Hidalgo/Dreamstime
Ancient global warming may have been caused by massive volcanic activity, scientists say, but this natural event does not come close to matching what humans are doing today.
Ancient volcanism sent huge amounts of carbon dioxide into the atmosphere during that time, which was then absorbed by the oceans over thousands of years, researchers have suggested in a new study.
The soaring carbon dioxide levels drove temperatures up by between 5°C and 8°C during a time period known as the Paleocene-Eocene Thermal Maximum (PETM), approximately 55 million years ago.
According to the researchers, the event triggered chemical reactions that caused waters to become highly acidic, killing many marine species and causing a deep-sea mass extinction.
However, the researchers warned that current human-led emissions are introducing carbon into the oceans up to eight times faster than those ancient volcanoes and the oceans are again absorbing much of it.
“If you add carbon slowly, living things can adapt. If you do it very fast, that’s a really big problem,” said Dr Bärbel Hönisch, a geochemist at Lamont-Doherty Earth Observatory at Columbia University, US.
Dr Hönisch added: “The past saw some really dire consequences and that does not bode well for the future. We’re outpacing the past and the consequences are probably going to be very serious.”
While scientists have known about the PETM carbon surge for decades, the reason behind this event has been unclear. Investigating this further, the researchers mimicked highly acidic ocean conditions in the lab, where they cultured tiny shelled marine organisms called foraminifera.
They compared the geochemical information gathered from the lab-grown organisms with the data from fossilised foraminifera from the PETM time period. This method allowed the researchers to calculate the amount of carbon added to the ocean during the PETM, which they say was as much as 14.9 quadrillion metric tons over about 5,000 years.
The researchers believe volcanoes to be the likely source of ancient carbon in the oceans, which possibly derived from massive eruptions centered around what is now Iceland.
They added that the carbon would have come from carbon dioxide emitted directly by the eruptions, the combustion of surrounding sedimentary rocks and some methane welling up from the depths.
According to the researchers, atmospheric levels have shot up from about 280 parts per million (ppm) in the 1700s to about 415ppm today and are on a path to keep rising rapidly. As oceans continue to absorb carbon dioxide, rapid acidification is starting to stress marine life.
“We want to understand how the Earth system is going to respond to rapid CO2 emissions now,” said Laura Haynes, an assistant professor at Vassar College in New York. “The PETM is not the perfect analogue, but it’s the closest thing we have. Today, things are moving much faster.”
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