[The_Victor]

Modern carbon dioxide input from fossil fuel sources to the earth's surface is approaching the same levels estimated for the PETM period, which raises concerns about future climate and changes in ocean circulation, say the scientists. Thus, they say, the Paleocene/Eocene example suggests that human-produced changes may have lasting effects not only on global climate, but on deep ocean circulation.

This conclusion cannot be logically supported. If CO2 levels at the PETM were similar to today, then a human cause cannot be a logical assumption, since man was not present at the PETM event.

[MoJoWork_n]

RE: "...conclusion cannot be logically supported..."

It really doesn't matter what the source of the CO2 was. In this case, since the climate change took place after the extinction of the dinosaurs, it's a 100% certainty that flatulence from sauropods had nothing to do with the warm up, either.

I'm sure that that's a huge comfort to the departed dinosaurs, as they continue to graze, ruminate and poot Big Ones, in the Elysian Aalanian Fields.

[cogitator]

If CO2 levels at the PETM were similar to today, then a human cause cannot be a logical assumption, since man was not present at the PETM event.

The "proof" of the causation of the current atmospheric CO2 levels as being primarily due to human activities is not reliant on the PETM. The main thing that the PETM does is show in the Earth system that greenhouse gases can force temperature changes (and apparently then cause some "downstream" effects).

[dufekin]

Some climatologists view carbon dioxide as a SYMPTOM rather than a CAUSE of [paleoclimatic episodes of] global warming. Warmer climates with adequate moisture enable various life forms to flourish (with greater biomass per unit land area) than cooler (or drier) climates permit.