New Haven, Conn. -- Global warming 55 million years ago suggests a high climate sensitivity to carbon dioxide, according to research led by Mark Pagani, associate professor of geology and geophysics at Yale and published in the December 8 issue of Science.

For some years, scientists have known that a massive release of carbon into the atmosphere caused the ancient global warming event known as the Paleocene-Eocene Thermal Maximum (PETM) that began about 55 million years ago. The geologic record shows that the resulting greenhouse effect heated the planet as a whole by about 9 F (5 C), in less than 10,000 years.

That temperature increase lasted about 170,000 years, altered the worlds rainfall patterns, made the oceans acidic, affected plant and animal life in the seas and on land, and spawned the rise of our modern primate ancestors.

"The PETM is a stunning example of carbon dioxide-induced global warming and stands in contrast to critics who argue that the Earths temperature is insensitive to increases in carbon dioxide," said Pagani. "Not only did the Earth warm by at least 9F (5C), but it did so during a time when Earths average temperature was already 9F warmer than today."

However, what has not been clear is how much carbon was responsible for the temperature increase and where it came from. Scientists have speculated that it might have come from massive fires from burning coal and other ancient plant material, or from burps of methane from the continental shelves that rapidly became atmospheric carbon dioxide.

"According to this work, if the PETM was caused by the burning of plant material then climate sensitivity to carbon dioxide is more than 4.5F (2.5C) per carbon dioxide doubling. And if methane was the culprit, then Earths climate must be extremely sensitive to carbon dioxide increasing, over 10F (5.6C) p
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Contact: Janet Rettig Emanuel
janet.emanuel@yale.edu
203-432-2157
Yale University
7-Dec-2006