Watts Up With That:
Global temperature reconstruction over the past 420,000 years derived from δ18O anomalies in air trapped in ice strata at Vostok station, Antarctica. To render the anomalies global, the values of the reconstructed anomalies (y axis) have been divided by the customary factor 2 to allow for polar amplification. Diagram based on Petit et al. (1999). Note that all four previous interglacial warm periods, at intervals of 80,000-125,000 years, were at least as warm as the current warm period. Data source: Petit et al. (1999). (not part of the Utah press release, provided for reference)
From the University of Utah
Size, duration were like modern climate shift, but in two pulses
SALT LAKE CITY, 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.
That is “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 wrote. Since 1900, human burning of fossil fuels emitted an average of 3 petagrams per year – even closer to the rate 55.5 million years ago.
Each pulse of carbon emissions lasted no more than 1,500 years. Previous conflicting evidence indicated the carbon release lasted anywhere from less than a year to tens of thousands of years. The new research shows atmospheric carbon levels returned to normal within a few thousand years after the first pulse, probably as carbon dissolved in the ocean. It took up to 200,000 years for conditions to normalize after the second pulse.
The new study 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, in terms of timing, that more likely causes included melting of seafloor methane ices known as clathrates, or volcanism heating organic-rich rocks and releasing 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, an associate professor of geology and geophysics at the University of Utah.
“This new study tightens the link,” he adds. “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.”
