The description and scientific study of climate. Descriptive climatology deals with the observed geographic or temporal distribution of meteorological observations over a specified period of time. Scientific climatology addresses the nature and controls of the earth's climate and the causes of climate variability and change on all timescales. The modern treatment of the nature and theory of climate, as opposed to a purely descriptive account, must deal with the dynamics of the entire atmosphere–ocean–land surface climate system, in terms of its internal interactions and its response to external factors, for example, incoming solar radiation. Applied climatology addresses the climate factors involved in a broad range of problems relating to the planning, design, operations, and other decision-making activities of climate sensitive sectors of modern society.