Climate and the General Circulation

Weather versus Climate

The atmosphere is the central component of the complex, connected, and interactive global environmental system upon which all life depends.

Climate may be broadly defined as the long-term behavior of this environmental system.

To understand fully and to predict changes in the atmospheric component of the climate system, one must understand the sun, oceans, ice sheets, solid earth, and all forms of life.

Earth's climate system is influenced by innumerable interacting variables. Click on the drawing on the left to find out more.
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There is an expression used by inhabitants of Denver, Colorado: "The climate is great, but the weather is awful!" The expression indicates that while the general or average weather in that area is delightful, with abundant sunshine and frequent clear, crisp days, the weather is very changeable, with occasional high winds, violent thunderstorms, snow squalls, and sometimes even tornadoes bursting upon the scene.

Weather is the moment-by-moment and place-by-place description of the state of the atmosphere, with events taking place on a small scale in both space and time. A fall day may begin warm and rainy, clear by midday, and finish with snow flurries.

Two examples of Weather are provided by the links below:

Climate, on the other hand, encompasses the totality of weather effects, accumulated over an extended period of time.

In order to describe the climate of a region, it is necessary to know the extremes as well as the averages.

It is one thing to know the mean annual temperature and rainfall of a place, but it is much more meaningful to know how hot it gets in the summer and how cold it gets in the winter; whether the rains tend to fall in thunderstorms or in extended drizzles; whether there are wet and dry seasons; and whether the place is subject to occasional high winds, tornadoes, or hurricanes.

The Climate of Tucson is illustrated in the following plots:

Climate is usually described in terms of normals, means, and extremes of a variety of weather elements including temperature, precipitation, and wind. By international convention, climate norms are computed from averages of weather elements compiled over a 30-year period.

The animations of the University of Oregon visualize the seasonal variations of, and interactions among a set of climate variables that describe the surface water and energy balances, temperature, and atmospheric circulation.