"The Earth is currently in an interglacial period of an ice age that started about two and a half million years ago. The Earth’s current ice age is primarily caused by Antarctica drifting over the South Pole 30 million years ago. This meant that a large area of the Earth’s surface changed from being very low-albedo ocean to highly reflective ice and snow. The first small glaciers were formed in Antarctica perhaps as long ago as 40 million years. They expanded gradually until, about 20 million years ago, a permanent ice sheet covered the whole Antarctic continent. About 10 million years later, glaciers appeared on the high mountains of Alaska, and about 3 million years ago, ice sheets developed on lower ground in high northerly latitudes.

Pacific Ocean bottom water temperatures started declining 40 million years ago, falling 10° C to the current 3° C. The band of high ocean temperatures (above 25° C) also contracted towards the equator, from 45° latitude to 20°. Eventually the oceans lost enough heat that the Earth’s orbital parameters started causing surges in ice formation. "

http://wattsupwiththat.com/2009/02/23/ice-ages-and-sea-level/#more-5804