If past climate change is any indication, Earth could be in store for some significant global warming according to research published in the December 8, 2006, issue of the journal Science. The work suggests that climate change skeptics may be fighting a losing cause.

The study, led by Mark Pagani, associate professor of geology and geophysics at Yale, looked at an episode of rapid climate change that occurred some 55 million years ago. Known as the Paleocene-Eocene Thermal Maximum (PETM), the period was marked by a rapid rise in greenhouse gases that heated Earth by roughly 9° F (5° C), in less than 10,000 years. The climate warming caused widespread changes including mass extinction in the world's oceans due to acidification and shifts of plant communities due to changes in rainfall. The era helped set the stage for the "Age of Mammals," which included the first appearance of modern primates.

The research, based on fossil records of terrestrial plants and oceanic plankton, suggests that the world's climate is highly sensitive to atmospheric carbon dioxide (CO2) levels, finding that a doubling of CO2 concentrations can raise global temperatures by at least 4 ºF (2.2 ºC). Current projections show that natural background atmospheric carbon dioxide levels are expected to double around mid-century due to fossil fuel combustion.

??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,? said Dr. Ken Caldeira, co-author of the study and a researcher at the Carnegie Institution??s Department of Global Ecology at Stanford University in California. ??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.?

http://news.mongabay.com/2006/1207-petm.html