Ice age

From Fiswiki

Ice age or, more precisely, "glacial age" is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers.

An ice age is a natural system. Within a long-term ice age, individual pulses of extra cold climate are termed "glacial periods" (or alternatively "glacials" or "glaciations"), and intermittent warm periods are called "interglacials".