Climate

Climate, sum of weather conditions, or the characteristic weather, of any area. Weather conditions include temperature, rainfall, sunshine, wind, humidity, and cloudiness. One method of studying climate is to use average figures, but these often conceal wide variations; for example, mean temperatures are of little value in regions of extreme cold or heat. Climatology was developed by the ancient Greeks. Around 500 B.C. Greek philosopher Par-menides suggested that 5 climatic zones encircle the earth: a tropical zone on either side of the equator, 2 temperate zones in the middle latitudes, and 2 cold zones around the poles. This classification was based on latitude, the most important factor affecting climate.

Long after the ancient Greeks, climatologists recognized that many factors besides latitude influence climate, for example, elevation, ocean currents, and variations in atmospheric pressure. In the early 1900s a German meteorologist, Vladimir Köppen, classified the world's climatic zones, combining temperature and rainfall boundaries with vegetation boundaries. He suggested 5 basic regions: tropical rainy climates with no cool season, dry climates, middle latitude rainy climates, northern forest climates, and polar climates with no warm season. Many other classifications exist, and each has its uses, but none takes into account all the features of climate. Paleoclimatologists, who study past climates through the record of rocks and fossils, have shown that climates have changed considerably during the earth's history. For example, coal seams in northern Canada show that swampy tropical forests once grew there. Several theories have been advanced to explain climatic change over time. The theory of continental drift suggests that the continents have moved in relation to the poles. Other theories include sunspots, variations in solar radiation, and changes in the earth's orbit or tilt. Climatologists have observed small changes in climate in the past 100 years. Their findings have raised speculation about our ability to influence climatic change.

See also: Weather.