About 10 million years after the dinosaurs went extinct our planet experienced a surge in the concentration of carbon dioxide in the atmosphere - a climate event called Paleocene-Eocene Thermal Maximum (PETM).

No one is certain what caused the PETM, but the event had turned temperatures to rise to 5 degrees Celsius (41 degrees Fahrenheit). The Earth continued to warm rapidly, and marine organisms went through die-offs because of ocean acidification.

Examining The Past

Today, scientists often look to the PETM as an analog for current rising temperatures.
In fact, a new study suggests that humans are putting more carbon into the atmosphere at a faster rate than what happened during the PETM.

Lead researcher Richard Zeebe, an oceanographer from the University of Hawaii, Manoa, said ecosystems need time to adjust.

"We're doing it faster and most likely the consequences are going to be more severe," said Zeebe.

Zeebe said that the only event they know at the moment that had a massive carbon release at a short period of time was 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," he said, adding that the PETM is so crucial because it is a possible window on our own situation.

A lot of carbon indeed injected themselves into the atmosphere during the PETM, and the warming event that followed it lasted more than 100,000 years. Precisely how rapid the emissions occurred is a different matter.

Facing The Future

Together with colleagues from the University of California-Riverside and the University of Bristol, researchers examined a deep ocean core of sediment from off the coast of New Jersey in order examined what happened during the PETM.

The research team's goal was to figure out the ratios between different isotopes of carbon and oxygen 56 million years ago. It is important to examine the relationship between the two because it would allow researchers to determine how levels of CO2 in the atmosphere influenced temperatures back then.

Zeebe and his colleagues found that there is a gap between time that massive pulses of carbon went into the atmosphere and subsequent warming, because the oceans have larger thermal inertia. A large lag time would suggest greater carbon release, while the lack of lag time would mean that CO2 came out slowly.

About 2,000 to 4,500 billion tons of carbon possibly injected themselves into the atmosphere during the PETM, and that is equivalent to 1 billion tons of carbon emissions per year. Now, humans are releasing 10 million tons of carbon emissions annually, which are impacting the Earth more rapidly.

What does this mean for our future? The PETM analogy to our own time is less than perfect, but it suggests that our own era is worse than what happened since the dinosaur extinction.

"The two main conclusions is that ocean acidification will be more severe, ecosystems may be hit harder because of the [carbon emission] rate," said Zeebe.

This also means that because the carbon emission rate is unprecedented, our planet has effectively entered an era of "no-analog" state, where there is no parallel for the rate of change. It represents a challenge that could constrain future climate projections.

The findings of the study are featured in the journal Nature Geoscience.

Photo: Anja Pietsch | Flickr

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