Milankovitch cycles essentially describe earth's relationship with the sun based on eccentricity, obliquity, and precession. Each of these three components operates on a different timescale, but when they overlap in just the right way, they can reduce insolation (the sunlight hitting the earth) and lower temperatures; conversely, when they work to increase insolation, temperatures go up. For more information on how these cycles influence climate, visit NASA, Skeptical Science, or Wikipedia. Read more