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Climate ChangeGlobal WarmingScience

Prehistoric Warming Mysteries

A new research paper published in the journal Nature Geoscience has drawn attention to the possibility that the Earth may be able to recover quicker than anticipated from rising carbon dioxide emissions.

This new theory is based on data gathered from studying the end of the Palaeocene-Eocene Thermal Maximum, which took place some 56 million years ago, and constitutes an approximately 170,000 year long period of global warming that, sadly, has much in common with Earth’s present-day conditions.

According to the research, the Earth increased its ability to pull carbon from the air, leading to a recovery that was quicker than models would have anticipated. That being said, the recovery is still measured in the order of tens of thousands of years.

“We found that more than half of the added carbon dioxide was pulled from the atmosphere within 30,000 to 40,000 years, which is one-third of the time span previously thought,” said Gabriel Bowen, the associate professor of earth and atmospheric sciences who led the study and who also is a member of the Purdue Climate Change Research Center. “We still don’t know exactly where this carbon went, but the evidence suggests it was a much more dynamic response than traditional models represent.”

“During this prehistoric event billions of tons of carbon was released into the ocean, atmosphere and biosphere, causing warming of about 5 degrees Celsius,” Bowen said. “This is a good analog for the carbon being released from fossil fuels today.”

Bowen worked with James Zachos, a professor of earth and planetary sciences at the University of California, Santa Cruz, to study the end of the Palaeocene-Eocene Thermal Maximum using samples of marine and terrestrial sediments deposited throughout the event. They measured the levels of two different types of carbon atoms.

“The rate of the carbon isotope change in rock minerals tells us how rapidly the carbon dioxide was pulled from the atmosphere,” he said. “We can see the fluxes of carbon dioxide in to and out of the atmosphere. At the beginning of the event we see a shift indicating that a lot of organic-derived carbon dioxide had been added to the atmosphere, and at the end of the event we see a shift indicating that a lot of carbon dioxide was taken up as organic carbon and thus removed from the atmosphere.”

There are several theories which explain how the Earth was able to develop a quick-fire method of withdrawing the carbon dioxide, but all have flaws. A rapid growth of forests, plants and carbon-rich soils could explain the recovery, says Bowen.

“Expansion of the biosphere is one plausible mechanism for the rapid recovery, but in order to take up this much carbon in forests and soils there must have first been a massive depletion of these carbon stocks,” he said. “We don’t currently know where all the carbon that caused this event came from, and our results suggest the troubling possibility that widespread decay or burning of large parts of the continental biosphere may have been involved.”

And release from a different source, such as volcanoes or sea floor sediments, may be what triggered the event.

“The release of carbon from the biosphere may have occurred as a positive feedback to the warming,” Bowen said. “The forests may have dried out, which can lead to die off and forest fires. If we take the Earth’s future climate to a place where that feedback starts to happen we could see accelerated rates of climate change.”

So with all the mysteries surrounding the Palaeocene-Eocene Thermal Maximum, Bowen and his team continue to study the carbon cycle, as well as investigating the changes in the water cycle.

“We need to figure out where the carbon went all those years ago to know where it could go in the future,” he said. “These findings show that the Earth’s response is much more dynamic than we thought and highlight the importance of feedback loops in the carbon cycle.”

Source: Purdue University
Image Source: Axel-D




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