The average temperature averages of 22 degrees Celsius (71.6 Farenheit) and high CO2 levels promoted a huge increase in plant life. Fossilized flora evidence suggests the presence of paleoforests up to latitudes of 85° in both Northern and Southern hemispheres. These forests would not have survived radical weather events that turned forests into burning infernos from lightning strikes and high winds to mow them down. It was these massive forests that created the oxygen levels to support animal life and, ultimately, human life.
There were forests up to 80 degrees Latitude in the Earth's past.