A theory is developed based on well established principles of physics and astronomy that correctly predicts the time and latitude of the retreat of the recent North American ice age and the warming observed BP.The role of green house gases in determining the temperature of Earth is also discussed in detail.Equations are derived and used to calculate the effects of changes in eccentricity of Earth's orbit, the spin axis tilt angle, and the direction of the spin axis(the precession angle) on the energy received from the sun at any point on Earth. The equations predict a quasi-periodic variation in energy received by Earth as the precession angle advances counterclockwise. Many graphs showing energy received by Earth as a function of latitude, precession and spin axis tilt angles and the orbital position of Earth are contained in the book.