Earth, Climate & Environment


Climate, the long-term effect of the sun's radiation on the rotating earth's varied surface and atmosphere. It can be understood most easily in terms of annual or seasonal averages of temperature and precipitation.

Land and sea areas, being so variable, react in many different ways to the atmosphere, which is constantly circulating in a state of dynamic activity. Day-by-day variations in a given area constitute the weather, whereas climate is the long-term synthesis of such variations. Weather is measured by thermometers, rain gauges, barometers, and other instruments, but the study of climate relies on statistics. Today, such statistics are handled efficiently by computers. A simple, long-term summary of weather changes, however, is still not a true picture of climate. To obtain this requires the analysis of daily, monthly, and yearly patterns. Investigation of climate changes over geologic time is the province of paleoclimatology, which requires the tools and methods of geological research. See Meteorology.

The word climate comes from the Greek klima, referring to the inclination of the sun. Besides the effects of solar radiation and its variations, however, climate is also influenced by the complex structure and composition of the atmosphere and by the ways in which it and the ocean transport heat. Thus, for any given area on earth, not only the latitude (the sun's inclination) must be considered but also the elevation, terrain, distance from the ocean, relation to mountain systems and lakes, and other such influences. Another consideration is scale: A macroclimate refers to a broad region, a mesoclimate to a small district, and a microclimate to a minute area. A microclimate, for example, can be specified that is good for growing plants underneath large shade trees.

Climate has profound effects on vegetation and animal life, including humans. It plays statistically significant roles in many physiological processes, from conception and growth to health and disease. Humans, in turn, can affect climate through the alteration of the earth's surface and the introduction of pollutants and chemicals such as carbon dioxide into the atmosphere. See Environment.