[palmer]

The main analogous factor is that the PETM is the only period in the Cenozoic where there was clearly a rapid rise in atmospheric greenhouse gases absent any other climate forcing agents. The resulting effect on global temperatures is pretty obvious.

Warming and CO2 increases are often coincident, but it doesn't mean one causes the other. The phrase "climate forcing agents" implies a degree of certainty that would come from a testable scientific theory rather than an artifact of computer models repeatedly shown to be wrong.

[cogitator]

Warming and CO2 increases are often coincident, but it doesn't mean one causes the other.

See what you think about the PETM after reading this:

Ocean Burps and Climate Change

The article posted says this:

"During the PETM, unknown factors released vast quantities of methane that had been lying frozen in sediment deposits on the ocean floor. After release, most of the methane reacted with dissolved oxygen to form carbon dioxide, which made the seawater more acidic. Acidic seawater corrodes the carbonate shells of microplankton, dissolving them before they can reach the ocean floor and reducing the carbonate content of marine sediment."

I also discovered, for the first time, that the triggering episode is thought to be plate-tectonic changes causing landslides on continental slopes.

Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties (2005), page 69

This page also indicates that there is a competing comet impact explanation for the PETM -- but I don't think Zachos ascribes to it.