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The climate of a state cannot be described by a single element such as temperature or precipitation. Climate also includes such elements as soil temperature, humidity, wind velocity and direction, atmospheric pressure, solar and terrestrial radiation, and snow cover. Climate is also determined in part by solid and liquid particulate matter and gases in the atmosphere. Besides oxygen, nitrogen, and water vapor, a list of the more important atmospheric constituents would include carbon dioxide, ozone, dust, smoke, salt particles, and sulphur and nitrogen oxides. Measurements of these minor constituents are either non-existent or so meager that a climatology cannot be presented. However, it should be remembered that all of these substances act together to determine our climate.

The climate of an area is one of its most important natural resources. Climate is similar to many other natural resources in that man must continually utilize its elements to produce food and material so that he can subsist. Climate differs from other natural resources, however, because it constantly affects him and he must live in it to exist.

Climate is a renewable resource and remains relatively constant from decade to decade and century to century. Exploitation of some natural resources, however, can result in increases of certain atmospheric constituents such as carbon dioxide and atmospheric aerosols, which also affect climate. Many scientists believe that such changes may produce a significant alteration of climate over relatively short time periods when considered on the time scale of natural climatic change.

Climatic information in this publication is based on the 30-year period, 1931-60, unless otherwise stated. This time period was selected because short-term fluctuations in weather records generally smooth out over that number of years. In addition, the years 1931-60 correspond with the time interval set by the World Meteorological Organization to facilitate comparison of world-wide weather records.

Much of the data in this publication has been presented in map rather than table form. This method of presentation allows anyone in the state to determine the climatic element for his particular location by merely interpolating for values between the lines. This can be done with little significant error at most North Dakota locations because changes in topography are not abrupt here as in mountainous areas. Although interpolations can also be made with caution from tables, interpolating data from maps where the patterns are evident is easier and more reliable.