New results on the rapid global warming 55 million years ago

In its 20th December issue, Nature reports on new results on a phase of rapid global warming 55 million years ago. This episode of climate change is seen as the best fossil analogue to predicted future climate trends. Lead-author is Appy Sluijs (Utrecht University, The Netherlands) and co-authors include Henk Brinkhuis, Gert-Jan Reichart (both Utrecht University), Stefan Schouten (Royal Netherlands Institute for Sea Research: NIOZ), Jaap Sinninghe Damste (NIOZ; UU), James C. Zachos (University of California at Santa Cruz), and Gerald R. Dickens (Rice University).

Analogous to the modern situation, the phase of greenhouse warming 55 million years ago was caused by a relatively rapid increase of CO2 concentrations in the atmosphere. This phase, known as the Palaeocene-Eocene thermal maximum, 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 part of the greenhouse gases was injected as a result of a chain-reaction of events. Likely through intense volcanism, CO2 concentrations in the atmosphere became higher and the ensuing greenhouse warmed the Earth. As a result, marine methane hydrates, ice-like structure in which massive amounts of methane are stored, melted and released large amounts of methane into the atmosphere. This 'positive feedback' amplified the magnitude of global warming, which comprised about 6 C in total. The study for the first time shows such a chain-reaction during rapid warming in a greenhouse world.

The new research confirms that climate warming can enforce mechanisms that inject massive amounts of stored carbon into the atmosphere. Current and future warming will likely see similar feedbacks, 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 55 million years ago tropical algae migrated into the Arctic Ocean, when temperatures rose to 24 C. Current climate models are not capable of simulating the high temperatures at that time, 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.