There is this idea amongst Denialists that climatologists don’t seem to know that Co2 levels have been higher in the past. According to the Denialist, not only is a climatologist a mad scientist already involved in the most successful world conspiracy of all time, with an evil agenda to create a COMMUNIST WORLD GOVERNMENT! (“Oh the humanity!“) but they can also seem to picture them as bumbling baffoons that don’t even know their own craft? How are they both the brilliant perpetrators of a world conspiracy and absolute morons that don’t know the history of earth’s climate as well? Oh the mind of a Denialist, who can fathom their ways?
Last year, the same group of researchers showed in Nature that tropical algae migrated into the Arctic Ocean during the PETM, when temperatures rose to 24oC. Current climate models are not capable of simulating such high temperatures in the Arcti, which has repercussions for the predictions of future climate change. In addition to Al Gore’s presentation, this type of research shows what a greenhouse world looks like, including palm trees and crocodiles in the Arctic.
The wiki also has an interesting introduction.
The Paleocene/Eocene boundary, 55.8 million years ago, was marked by the most rapid and significant climatic disturbance of the Cenozoic Era. A sudden global warming event, leading to the Paleocene–Eocene Thermal Maximum (PETM, alternatively “Eocene thermal maximum 1” (ETM1), and formerly known as the “Initial Eocene” or “Late Paleocene Thermal Maximum”, (IETM/LPTM)), is associated with changes in oceanic and atmospheric circulation, the extinction of numerous deep-sea benthic foraminifera, and a major turnover in mammalian life on land which is coincident with the emergence of many of today’s major mammalian orders.
The event saw global temperatures rise by around 6°C (11°F) over 20,000 years, with a corresponding rise in sea level as the whole of the oceans warmed. Atmospheric carbon dioxide (CO2) concentrations rose, causing a shallowing of the lysocline. Regional deep water anoxia may have played a part in marine extinctions. The event is linked to a negative excursion in the δ13C isotope record, which occurs in two short (~1,000 year) pulses. These probably represent degassing of clathrates (“methane ice” deposits), which accentuated a pre-existing warming trend. The release of these clathrates, and ultimately the event itself, may have been triggered by a range of causes. However, an alternative mechanism has also been proposed.
Also very good on this is the free online movie Crude, the Incredible Journey of oil