Tobject]user: an extended period when temperatures are well below average is known as a/an
a. ice age.
b. draft.
c. cold wave.
d. drought.

The answer is A.
Ice Age or glacial period refers to the extended period of well-below-average temperatures. It is a prolonged period where reduction in the temperature of the Earth’s surface and atmosphere are caused by the expansion of continental and polar ice sheets and alpine glaciers. Usually this phenomenon occurs in the northern and southern hemispheres where extensive ice sheets are seen most. 

At present we are now experiencing an interglacial period after the Holocene Ice age