What Was It Like The Last Time CO2 Levels Were This High?
Pliocene megabiomes, image: Wikipedia. The following post from
Skeptical Science is by John Cook.  A vivid picture of our
climate's future can be found in our past. Currently,
atmospheric carbon dioxide (CO2) levels have reached 390 parts
per million (ppm). The last time CO2 was that high was around 3
million years ago, in the early Pliocene. Back then, CO2 levels
remained at around 365 to 410 ppm for thousands of years.
Consequently, the Pliocene gives us vital clues of the long-term
effects of raised CO2 levels. New research has just been
published that examines this period and confirms previous
findings that  the Pliocene was dramatically warmer than current
temperatures.The research, published in Csank et al 2011, uses
two independent methods to measure Arctic temperature during the
Pliocene, on Ellesmere Island. They find that Arctic
temperatures were 11 to 16°C warmer. This is consistent with
other independent estimates of Arctic temperature at