Originally Posted by: R. ShackleferdTo be absolutely fair, you can't say it's higher than it's ever been ....

Quite right, even with the typo.

I managed to upset myself a bit when I read about the >Paleocene-Eocene Thermal Maximum< that I saw referred to in one of the posts on that RealClimate disussion you linked.

What stopped my panic was this:
"Atmospheric carbon levels then are thought to have been about 2-3,000 parts per million (ppm), compared with almost 380 ppm today."