There have been many ice ages during the last 2.6 million years but when people talk about the Ice Age, they are often referring to the most recent glacial period, which peaked about 21,000 years ago and ended about 11,500 years ago. What causes ice ages is not completely understood. The composition of the atmosphere, changes in the position of our planet around the Sun, and changes in ocean currents are some of the important factors that control the climate.