is this changing?
Yes, the Earth has undergone periodic climate shifts in the past, including four major ice ages.
Climate
Earth has undergone periodic climate shifts in the past, including four major ice ages. 
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.
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Climate [SEP] Climate change
The UNFCCC uses "climate variability" for non-human caused variations. Earth has undergone periodic climate shifts in the past, including four major ice ages. These consisting of glacial periods where conditions are colder than normal, separated by interglacial periods. The accumulation of snow and ice during a glacial period increases the surface albedo, reflecting more of the Sun's energy into space and maintaining a lower atmospheric temperature. Increases in greenhouse gases, such as by volcanic activity, can increase the global temperature and produce an interglacial period. Suggested causes of ice age periods include the positions of the continents, variations in the Earth's orbit, changes in the solar output, and volcanism.