Three orbital processes play a role in climate variability.

Eccentricity - This orbital parameter describes the shape of the Earth's orbit around the Sun.  If the orbit's shape we a perfect circle, its eccentricity would be zero.  In fact, due to the multiple gravitational forces acting on the Earth, the orbit is more oval or elliptical in shape and changes through time (by about 7%). The most important of the eccentricity cycles are a 400,000 year cycle and a pair of cycles (a doublet) close to 100,000 years. Eccentricity affects climate because the shape of the orbit determines the Earth-Sun distance along the orbit, and thus how much sunlight reaches the Earth at different seasons. One of the great mysteries in climate research, however, is how small changes in the the Earth's orbit are amplified into large climate responses.