Climatic Chain Reaction Caused Runaway Greenhouse Effect 55 Million Years Ago

Analogous to the Earth's current situation, greenhouse warming 55 million years ago was caused by a relatively rapid increase of CO₂ concentrations in the atmosphere. This phase, known as the Paleocene-Eocene thermal maximum (PETM), was studied using sediments that accumulated 55 million years ago on the ocean floor in what is now New Jersey.

The new study shows that a large proportion of the greenhouse gases was released as a result of a chain-reaction of events. Probably due to intense volcanic activity, CO₂ concentrations in the atmosphere became higher and the ensuing greenhouse effect warmed the Earth. As a result, submarine methane hydrates (ice-like structures in which massive amounts of methane are stored) melted and released large amounts of methane into the atmosphere.

This further amplified the magnitude of global warming, which comprised about 6^o C in total. The study is the first to show such a chain reaction during rapid warming in a 'greenhouse world'.

The new research confirms that global warming can stimulate mechanisms that release massive amounts of stored carbon into the atmosphere. Current and future warming will likely see similar effects, such as methane hydrate dissociation, adding additional greenhouse gases to those resulting from fossil fuel burning.

Last year, the same group of researchers showed in Nature that tropical algae migrated into the Arctic Ocean during the PETM, when temperatures rose to 24^oC. Current climate models are not capable of simulating such high temperatures in the Arcti, which has repercussions for the predictions of future climate change. In addition to Al Gore’s presentation, this type of research shows what a greenhouse world looks like, including palm trees and crocodiles in the Arctic.

Journal Article: ‘Environmental precursors to rapid light carbon injection at the Palaeocene/Eocene boundary’ by Appy Sluijs, Henk Brinkhuis, Stefan Schouten, Steven M. Bohaty, Cédric M. John, James C. Zachos, Gert-Jan Reichart, Jaap S. Sinninghe Damsté, Erica M. Crouch & Gerald R. Dickens. Nature. December 20, 2007.

Lead author is Appy Sluijs (Utrecht University, The Netherlands) and co-authors include Henk Brinkhuis, Gert-Jan Reichart (both from Utrecht University), Stefan Schouten (Royal Netherlands Institute for Sea Research: NIOZ), Jaap Sinninghe Damsté (NIOZ, UU), James C. Zachos (University of California at Santa Cruz), and Gerald R. Dickens (Rice University).