Originally Posted by
cooker
It sounds like you posted that article to support the claim that volcanoes release more CO2 than humans.
Here is the gist of that article. About 20 million years ago, CO2 levels were at 400 ppm, perhaps due to intense volcanic activity....
There is now evidence to suggest that the Earth's largest extinction event, the end-Permian extinction, was probably biological in origin, with volcanism only a contributing factor.
Quote from
one of numerous articles on the subject:
"
The team's research indicates that the catastrophic event was in fact triggered by the tiniest of organisms, a methane-releasing microbe called Methanosarcina. New evidence suggests that at the time of the extinction, the microbes appeared in massive numbers across the world's oceans, spreading vast clouds of the carbon-heavy gas methane into the atmosphere. This had the effect of altering the planet's climate in a way that made it inhospitable to most other forms of life inhabiting Earth at that time.
It was previously believed that the mass extinction, known as the end-Permian extinction, was due to either vast amounts of volcanic activity, a devastating asteroid strike or prolific all-consuming coal fires...."
Just to be clear, this is a completely different event than the miocene epoch warm period you're talking about, but it does demonstrate how little we know for certain about the causes of past climate fluctuations, and it indicates that biological factors can indeed overshadow the influence of geological factors. Plus it's a fascinating discovery!