how can these ages be defined?
This is a long period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers.
Ice age
An ice age is a long period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. 
the climate of canada can best be described as __ UNANSWERABLE what is climate? It is the long-term average of weather, typically averaged over a period of 30 years. are there models to represent this ? Yes, these models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface and ice. is this changing? Yes, the Earth has undergone periodic climate shifts in the past, including four major ice ages.
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Ice age [SEP] Introduction
An ice age is a long period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and greenhouse periods, during which there are no glaciers on the planet. Earth is currently in the Quaternary glaciation, known in popular terminology as the Ice Age. Individual pulses of cold climate within an ice age are termed "glacial periods" (or, alternatively, "glacials", "glaciations", "glacial stages", "stadials", "stades", or colloquially, "ice ages"), and intermittent warm periods within an ice age are called "interglacials" or "interstadials", with both climatic pulses part of the Quaternary or other periods in Earth's history.