The major players in our climate appear to be Solar Activity, Volcanic Activity and Orbital Variation. As far as a biologically derived influence, my guess would be that at this point Oceanic Plankton Biomass has a greater effect then Human generated CO2.
Do not forget the moon.The moon causes atmospheric tides just as the moon affects the oceanic tides. It appears that you can expect colder temperatures when the moon is full or new due to this effect.
http://www.angelfire.com/moon/effects_our_weather/