By analysing a warming event 55 million years ago, geologists have an analogy to current climate change conditions, they claim.
Pushing global temperatures past a certain threshold, or tipping point, is likely to trigger a series of positive feedback mechanisms leading to the release of large quantities of greenhouse gases and even more rapid warming, the geologists said at the 34th International Geological Congress, being held in Brisbane, Australia.
“The PETM [Paleocene-Eocene Thermal Maximum] was a short term, very rapid, very extreme warming,” said David Greenwood, a paleoclimatologist from Brandon University in Canada. “Because it’s a short term event, it offers some insight into the kind of warming we’re experiencing now.”
Catastrophic change in carbon cycle
A drastic increase of greenhouse gases in the atmosphere at the end of the Paleocene and the beginning of the Eocene, about 55 million years ago, caused an increase in global temperatures by about 6ºC, which was sustained for nearly 150,000 years.
It is unclear what caused the initial warming, but it resulted in a catastrophic change in the global carbon cycle, said Gabriel Bowen from the University of Utah in Salt Lake City, USA. This would have triggered a series of additional, positive feedback mechanism that exacerbated the warming. These could have included the release of carbon from thawing permafrost soils, reduced growth of biosynthetically active plants or changes in the burial rate of carbon in the soil.
“This combination of feedbacks sustained atmospheric carbon dioxide levels at high levels for a period of tens to hundred thousand years,” said Bowen. “If those same feedbacks come into place, then this initial perturbation [of the carbon cycle] that we’re having right now through the burning of fossil fuels may have a much longer timespan than we’d like to.”