The founder of greenpeace testimony is either being misquoted or he hasn't done his research. The increase in CO2 levels corresponded with a global change in temperatures of around +10 degrees C. This was at the time of "snowball earth" when antarctic temperatures were experienced on a global scale. The earth was literally a "snowball". The only living creatures most likely existed in the ocean depths.
The increase in temperature was from a very low base and I'm not certain but I think it was in the Deccan Traps in India that the massive volcanic eruptions responsible for the increase in CO2 occurred. These eruptions went on for a million or so years and pulled the earth out of what was probably a permanent ice-age.
Following the retreat of the glaciers during the carboniferous era of the late palaeocene, land plants and ocean life developed in a luxuriant tropical environment, and locked away much of the CO2 in the atmosphere and forming the coal and oil deposits that we utilise today.
