What is an Ice Age??
An ice age is a period of long-term reduction in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and alpine glaciers. Glaciologically, ice age is often used to mean a period of ice sheets in the northern and southern hemispheres; by this definition we are still in an ice age.
Glacials and Interglacials
Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials. Within the ice ages (or at least within the last one), more temperate and more severe periods occur. The colder periods are called glacial periods, the warmer periods interglacials. Glacials are characterized by cooler and drier climates over most of the glaciations. Since the Earth has significant continental glaciation in the Arctic and Antarctic, we are currently in a glacial minimum of a glaciation. Such a period between glacial maxima is known as an interglacial.
Changes in Earth's atmosphere
The most revelant change is in the quantity of greenhouse gases in the atmosphere. There is evidence that greenhouse gas levels fell at the start of ice ages and rose during the retreat of the ice sheets, but it is difficult to establish cause and effect. Greenhouse gas levels may also have been affected by other factors which have been proposed as causes of ice ages.
There are three known configurations of the continents which block or reduce the flow of warm water from the equator to the poles:
A continent sits on top of a pole, as Antarctica does today
A polar sea is almost land-locked, as the Arctic Ocean is today.
A super continent covers most of the equator, as Rodinia did during the Cryogenian period.
Since today's Earth has a continent over the South Pole and an almost land-locked ocean over the North Pole, geologists believe that Earth will continue to experience glacial periods in the geologically near future.