What triggered the Palaeocene-Eocene thermal maximum (PETM) about 55 million years ago, which saw the fastest period of warming documented in Earth’s geological history? The PETM is associated with a rapid rise in greenhouse gases, particularly methane — but the big question is where did the methane come from?

bog.jpgThe most common answer has been the ocean (methane hydrates), but new research in Nature ($ub. req’d) casts doubt on the ocean theory — instead finding chemical evidence that the methane came from terrestrial sources, bogs, which were themselves stimulated by rising temperatures — an amplifying feedback. The lead author says:

A lot of temperate and polar wetlands are going to be wetter, and of course warmer as well [because of current climate change]. That implies a switch to more anaerobic conditions which are more likely to release methane. That’s what’s predicted, and that would be a positive feedback — and we have evidence now that this is what happened.

Indeed, research from last year found “thawing Siberian bogs are releasing more of the greenhouse gas methane than previously believed.” Why should we care about the source of the PETM?

Consider what scientists found when they analyzed data from a major expedition to retrieve deep marine sediments beneath the Arctic to understand the PETM, which they describe as a “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” This 2006 study, published in Nature ($ub. req’d), found Arctic temperatures almost beyond imagination — above 23°C (74°F) — temperatures more than 18°F warmer than current climate models had predicted, when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.

That our climate models are underestimating global warming is a point I have made many times. If bogs were a major amplifying feedback for the PETM, we may be in for “widespread, extreme climatic warming” if we don’t act quickly to slash greenhouse-gas emissions before the same feedbacks kick in again this century.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.