An ice age is a period in which the earth's climate is colder than normal, with ice sheets capping the poles and glaciers dominating higher altitudes. Within an ice age, there are varying pulses of colder and warmer climatic conditions, known as 'glacials' and 'interglacials'. Even within the interglacials, ice continues to cover at least one of the poles. In contrast, outside an ice age temperatures are higher and more stable, and there is far less ice all around. The earth has thus far made it through at least five significant ice ages.
This is a companion discussion topic for the original content at https://www.worldhistory.org/Ice_Age/.