Interesting documentry on channel 4 tonight about global warming. It seems that there is very strong evidence that although CO2 levels historically have been high when the earth warms up, the level of CO2 LAGS the temperature rise so isn't the cause, but a symptom. However there is historically excellent evidence that earth temperature follows sun activity. The stronger the sun activity the stronger it's magnetic field, and the more cosmic rays are deflected away from earth. Apparently the cosmic rays entering a water laden atmosphere form clouds which reflect the sun, so when the cosmic rays are at a low, so is the cloud cover and up the temperature goes. After a considerable lag the ocean temperature rises a bit, and as CO2 is less soluble in warm water than cold water, more is released into the atmosphere. Apparently the volume of CO2 dissolved in the oceans and naturally being released is orders of magnitude greater than anything man is releasing. Small changes in sea temperature alter the balance.