Several Ice Ages mark the history of the planet Earth.
One occurred in the distant past in the age of early Humans (DW: An Unearthly Child) and Neanderthals (DW: Ghost Light) During this time, an Ice Warrior craft from Mars crashed and buried itself. (DW: The Ice Warriors)
Earth suffered another ice age circa the year 5000, a time period visited by the Doctor during an unknown incarnation (DW: The Talons of Weng-Chiang) and, later in his life, during his eighth incarnation , EDA: Emotional Chemistry.
Other information
The Doctor met the de-thawed Ice Warriors in a future time period. We do not know for certain if this occurred circa 5000 or earlier or later. (DW: The Ice Warriors)
Behind the Scenes
Publicity material forThe Ice Warriors set that story in the year 3000.