Atmosphere Absorbing CO2 Faster Than PETM, When Dinosaurs Perished

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Conchs (Strombus alatus) kept in seawater under different levels of atmospheric carbon dioxide to effects of increased ocean acidity ( Kleindinst)
Conchs (Strombus alatus) kept in seawater under different levels of atmospheric carbon dioxide to effects of increased ocean acidity ( Kleindinst)

A new study in Nature Geoscience, led by Richard Zeebe of the University of Hawaii, looked at an anomalous time period called the Palaeocene-Eocene Thermal Maximum, or PETM. This phenomenon occurred about 56 million years ago, about ten million years following the beginning of the Cenozoic era (Age of Mammals), just about when the dinosaurs became extinct.

During the PETM, concentrations of carbon dioxide in the atmosphere spiked by 5 degrees Celsius, far higher than they have risen since human preindustrial levels 200 years ago. Climate scientists and world policy makers agree that 2 degrees more is all humans can probably take—or maybe 1.5, as more cautious voices are warning.

Zeebe’s expert team of researchers used a new technique to extract rates of change in a deep sedimentary record from the New Jersey shelf. They based their analysis on the relative timing of climate and carbon cycle changes. An age model was not necessary.

Cenozoic pCO2 and stacked deep-sea benthic foraminifer oxygen isotope curve for 0 to 65 Ma. Updated from Zachos et al. and converted to the Gradstein timescale ( applied the new method to stable carbon and oxygen isotope records using time-series analysis and carbon cycle–climate modeling. By doing so, they determined the ratios between different isotopes of carbon and oxygen found in PETM sediments.

The investigation indicates that earth’s population now is emitting carbon into the atmosphere faster than carbonization at any other time in earth’s history since the PETM. Zeebe explains:

Current and PETM rates of atmospheric carbonization over time (“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. 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.”

In fact, our current rate of anthropogenic carbon release is at least an order of magnitude (10x) higher than what the world experienced during the PETM. The study concludes that “given that the current rate of carbon release is unprecedented throughout the Cenozoic, we have effectively entered an era of a no-analogue state.” In other words, earth has apparently never seen a situation like today’s for at least 66 million years, if ever. At that time, the hothouse world lasted over 1,000 centuries.

Atmospheric CO2 and ice-free periods on the geologic time scale (

Weather Underground scientists provide the following description of the PETM:

“There are a lot of uncertainties surrounding the PETM—this extremely warm geologic period has been notoriously difficult to recreate, but recent advancements in understanding the warming have been made. Uncertainties should not be interpreted as misunderstanding. Instead, they should be treated a testament to how sensitive the climate system could be, and how influential humans are on the delicate global energy balance. It is clear that the earth dumped almost all of its stored carbon into the atmosphere, and now we are doing the same by pulling fossil fuels out of the ground and burning them. Just like the previous great global warming did, we are likely catapulting ourselves into a new geologic era: the Anthropocene.”

The abstract for the Nature Geoscience paper concludes:

“Given currently available records, the present anthropogenic carbon release rate is unprecedented during the past 66 million years. We suggest that such a ‘no-analogue’ state represents a fundamental challenge in constraining future climate projections. Also, future ecosystem disruptions are likely to exceed the relatively limited extinctions observed at the PETM.”

Zeebe says the two main conclusions are that ocean acidification will be more severe this time around, and that existing ecosystems may be hit harder because of the higher rate of carbon release.

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