Stanford, CA -- Scientists, including Ken Caldeira of the Carnegie Institutions Department of Global Ecology, have found that the Earths global warming, 55 million years ago, may have resulted from the climates high sensitivity to a long-term release of carbon. This finding contradicts the position held by many climate-change skeptics that the Earth system is resilient to such emissions. The work, led by Mark Pagani of Yale University, is published in the December 8, 2006, issue of Science magazine.

For some years scientists have known that an ancient global warming event, called the Paleocene-Eocene Thermal Maximum (PETM) beginning about 55 million years ago, was caused by a massive release of carbon. The geologic record shows that the ensuing greenhouse effect heated the planet by about 9 F (5 C), on average, in less than 10,000 years. The temperature increase lasted 170,000 years and caused profound changes to the worlds rainfall patterns, made the oceans acidic, and affected oceanic and terrestrial plant and animal life, including spawning the rise of our modern primate ancestors. But understanding just how much carbon was responsible for the temperature increase and where it came from remains elusive.

The new calculations used data from carbon found in fossils of ancient land plants and tiny marine organisms known as plankton. "We can tell that the amount of carbon released to the atmosphere and ocean was more or less the same as what is available today as coal, oil, and gas," Caldeira explained. "The carbon heated up the Earth for over 100,000 years. If the climate was as insensitive to CO2 as the climate skeptics claim, there would be no way to make the Earth so warm for so long."

The source of this ancient carbon is still a mystery. It might have come from massive fires burning coal and other ancient plant material, or it could have come from "burps" of methane from the continental shelves.

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Contact: Ken Caldeira
kcaldeira@globalecology.stanford.edu
650-704-7212
Carnegie Institution
7-Dec-2006