OVERVIEW 

Identify the controlling factors that affect climate.

OUTLINE

The variation of climatic elements from place to place and from season to season is due to several factors called climatic controls. The same basic factors that cause weather in the atmosphere also determine the climate of an area. These con-trols, acting in different combinations and with varying intensities, act upon temperature, precipi-tation, humidity, air pressure, and wind to pro-duce many types of weather and therefore climate. Four climatic controls largely determine the climate of every ocean and continental region. These controls are latitude, land and water distribution, topography, and ocean currents. Another factor which is now significant in deter-mining a regions climate is man. Mans influence on climate through pollution, deforestation, and irrigation, is now considered a climatic factor.

Perhaps no other climatic control has such a marked effect on climatic elements as does the latitude, or the position of Earth relative to the Sun. The angle at which rays of sunlight reach Earth and the number of Sun hours each day depends upon the distance of the Sun from the equator. (See fig. 6-5-1.) Therefore, the extent to which an air mass is heated is directly influenced by the latitude. Latitude influences the sources and direction of air masses and the weather they bring with them into a region.

The importance of latitude as a climatic control can be shown by comparing an equatorial area to a polar area. In the former, the Sun is close to being directly overhead during the day throughout the year. Therefore, there is little difference between mean temperatures for the coldest and warmest months. In the polar area, however, the Sun never rises far above the horizon; that is, the angle of the Sun to Earths surface is always acute. The radiant energy received per unit area is therefore slight, and the warming effects of the Sun are relatively weak. The average world surface temperatures are represented on two world charts for January and July in figures 3-1-4A and 3-1-4B. These are mean charts and are not meant to be an accurate por-trayal of the temperatures on any one particular day. Note that in general the temperatures decrease from low to high latitudes.

Figure 6-5-1.Latitude differences in amount of insolation.

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