[font face=Serif][font size=5]Past Global Warming Similar to Today’s[/font]

[font size=4]Size, Duration Were Like Modern Climate Shift, but in Two Pulses[/font]

[font size=3]Dec. 15, 2014 – The rate at which carbon emissions warmed Earth’s climate almost 56 million years ago resembles modern, human-caused global warming much more than previously believed, but involved two pulses of carbon to the atmosphere, University of Utah researchers and their colleagues found.

The findings mean the so-called Paleocene-Eocene thermal maximum, or PETM, can provide clues to the future of modern climate change. The good news: Earth and most species survived. The bad news: It took millennia to recover from the episode, when temperatures rose by 5 to 8 degrees Celsius (9 to 15 degrees Fahrenheit).

“There is a positive note in that the world persisted, it did not go down in flames, it has a way of self-correcting and righting itself,” says University of Utah geochemist Gabe Bowen, lead author of the study published today in the journal Nature Geoscience. “However, in this event it took almost 200,000 years before things got back to normal.”

Bowen and colleagues report that carbonate or limestone nodules in Wyoming sediment cores show the global warming episode 55.5 million to 55.3 million years ago involved the average annual release of a minimum of 0.9 petagrams (1.98 trillion pounds) of carbon to the atmosphere, and probably much more over shorter periods.

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Press Release 14-171
[font face=Serif][font size=5]Back to the future? Past global warming period echoes today's[/font]
[font size=4]Size, duration were like modern climate change[/font]

December 15, 2014

[font size=3]The rate at which carbon emissions warmed Earth's climate almost 56 million years ago resembles modern, human-caused global warming much more than previously believed, but involved two pulses of carbon to the atmosphere, researchers have found.

The findings mean that the so-called Paleocene-Eocene thermal maximum, or PETM, can provide clues to the future of modern climate change.

The good news: Earth and most species survived.

The bad news: It took millennia to recover from the episode, when temperatures rose by 5 to 8 degrees Celsius (9 to 15 degrees Fahrenheit).

"There is a positive note in that the world persisted, it did not go down in flames, it has a way of self-correcting and righting itself," says University of Utah geochemist Gabe Bowen, lead author of a paper published today in the journal Nature Geoscience.

"However, in this event it took almost 200,000 years before things got back to normal."

Using continental drilling boreholes from the Bighorn Basin of Wyoming, "these researchers have revealed for the first time that two rapid carbon release events occurred in the beginning of the PETM about 55.5 million years ago, the warmest period for the past 65 million years on Earth," says Yusheng (Chris) Liu, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research.

Bowen and colleagues report that carbonate or limestone nodules in Wyoming sediment cores show that the global warming episode 55.5 million to 55.3 million years ago involved the average annual release of a minimum of 0.9 petagrams (1.98 trillion pounds) of carbon to the atmosphere, and probably much more over shorter periods.

That's "within an order of magnitude of, and may have approached, the 9.5 petagrams (20.9 trillion pounds) per year associated with modern anthropogenic carbon emissions," the researchers write in their paper.

Since 1900, human burning of fossil fuels has emitted an average of 3 petagrams per year--even closer to the rate 55.5 million years ago.

Each past pulse of carbon emissions lasted no more than 1,500 years. Previous conflicting evidence indicated that the carbon release lasted anywhere from less than a year to tens of thousands of years.

The new research shows that atmospheric carbon levels returned to normal within a few thousand years after the first pulse, probably as carbon dissolved in the ocean.

200,000 years for conditions to normalize

After the second pulse, it took up to 200,000 years for conditions to normalize.

The research also ruled as unlikely some theorized causes of the warming episode, including an asteroid impact, slow melting of permafrost, burning of organic-rich soil or drying out of a major seaway.

Instead, the findings suggest that more likely causes included melting of seafloor methane ices known as clathrates, or volcanism that heated organic-rich rocks and released methane.

"The Paleocene-Eocene thermal maximum has stood out as a striking, but contested, example of how 21st-century-style atmospheric carbon dioxide buildup can affect climate, environments and ecosystems worldwide," says Bowen.

"This new study tightens the link. Carbon release back then looked a lot like human fossil-fuel emissions today, so we might learn a lot about the future from changes in climate, plants and animal communities 55.5 million years ago."

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