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Climatology studies the statistical behaviour of the atmosphere and its coupling to oceans, ice and the land over extended periods. It asks how distributions of temperature, rainfall, wind and other quantities vary with location, season and external forcing. A climatological normal provides one stated reference, but an average alone does not describe extremes or variability.
Measurements from weather stations and other observing systems test climate models and establish changes relative to a baseline. Physical interpretation requires energy and moisture budgets, atmospheric circulation and interactions such as ice-ocean albedo feedback. An unusually cold day and a long-term warming trend concern different statistical questions, so the time interval and the measured quantity must be specified.