Civilization was nice while it lasted…
If you dig deep enough into the Earth’s climate change archives, you hear about the Palaeocene-Eocene Thermal Maximum, or PETM. And then you get scared.
This is a time period, about 56 million years ago, when something mysterious happened — there are many ideas as to what — that suddenly caused concentrations of carbon dioxide in the atmosphere to spike, far higher than they are right now. The planet proceeded to warm rapidly, at least in geologic terms, and major die-offs of some marine organisms followed due to strong acidification of the oceans.
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“If you look over the entire Cenozoic, the last 66 million years, the only event that we know of at the moment, that has a massive carbon release, and happens over a relatively short period of time, is the PETM,” says Zeebe. “We actually have to go back to relatively old periods, because in the more recent past, we don’t see anything comparable to what humans are currently doing.”
That’s why this time period is so crucial to study — as a possible window on our own.
There’s no doubt that a lot of carbon — about as much as contained the fossil fuel reserves that humans have either already burned, or could still burn, combined — made its way into the atmosphere during the PETM. The result was a major warming event that lasted over 100,000 years. But precisely how rapidly the emissions occurred is another matter.
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The geologic evidence from the new core did not show a lag, the new study reports. That means, the authors estimate, that while a gigantic volume of carbon entered the atmosphere during the PETM — between 2,000 and 4,500 billion tons — it played out over some 4,000 years. So only about 1 billion tons of carbon were emitted per year. In contrast, humans are now emitting about 10 billion tons annually — changing the planet much more rapidly.
“The anthropogenic release outpaces carbon release during the most extreme global warming event of the past 66 million years, by at least an order of magnitude,” writes Peter Stassen, an Earth and environmental scientist at KU Leuven, in Belgium, in an accompanying commentary on the new study.