Ancient global warming shows the limits of our knowledge

The scenario should sound familiar. The amount of carbon in the oceans and atmosphere changes suddenly and dramatically. The oceans are acidified and significant extinctions result. On land, global temperatures increase anywhere from five to nine degrees Celsius, causing widespread habitat disruptions. Despite the sudden onset of the event, its impact lingers for 100,000 years. 

This might sound like a worst-case situation for the current anthropogenic influences on climate, but it’s actually an historic event that the public is generally unaware of: the Paleocene-Eocene Thermal Maximum, or PETM, which occurred about 55 million years ago.

If there’s a gap between the scientific community and the public when it comes to climate change, the PETM is pretty illustrative. While portions of the public are still arguing over whether changes in atmospheric carbon dioxide are likely to do anything bad to us, the scientific community has concluded that, based on everything we know, the sudden change in carbon was a significant contributor to the rise in global temperatures and drop in oceanic pH that occurred during the PETM.

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