While the cause of ice ages are not fully known, the general consensus is that one major factor is important, Atmospheric composition. The concentrations of carbon dioxide and methane greatly effect the Earth's atmosphere and a major change in these concentrations could cause an ice age.

The causes of the ice age are presumed to be because of evolution, decreased solar activity, increased volcanic activity and altered ocean current flows. You can find more information here: http://en.wikipedia.org/wiki/Little_Ice_...