The weather conditions found in a certain place over a long period of time are known collectively known as the climate. Knowing about an area's climate can tell many things about life there, such as what kinds of plants can grow and what kinds of animals can survive. Among other things, climate information can help people decide which crops to plant, prepare for natural disasters, or choose the best season to travel to a vacation spot.

Factors that affect climate

The sun does not hit all areas of the Earth evenly. A region's latitude, or position north or south of the equator, determines the angle at which the sun's rays will strike it. Much more energy from the sun is received near the equator than at the North and South poles. (See also Antarctica and Arctic regions.)

Oceans cover about 70 percent of the Earth's surface. Thus, their influence on climate is great. Bodies of water help keep temperatures in the areas around them from getting extreme (not so cold in the winter and not so hot in the summer). Ocean currents also play a role in climate because they carry warm water in some directions and cold water in other directions.

Wind is another factor in determining climate. Winds vary in their temperature and in the amount of moisture they contain. Some regions get great winds known as monsoons, which often carry heavy rains.

The type of land in an area affects the climate. For example, mountain ranges can block cold air from many regions. Also, places that are at higher elevations are cooler than nearby places at lower elevations.

Clouds influence climate as well. Temperatures tend to be less extreme in areas with heavy cloud cover. During daylight and in summer, these clouds reduce the amount of heat received from the sun, keeping the area cooler. During the night and in winter, clouds reduce the amount of heat released back into space, keeping the area warmer.

While most things that affect climate are natural, human activity has been found to have some influence as well. During the 20th century scientists discovered that the Earth is slowly getting warmer. They believe the cause to be greater amounts of certain gases in the atmosphere. These gases trap additional heat on Earth. Much of the increase in these gases, especially carbon dioxide, is a result of people burning fossil fuels such as the gasoline used in automobiles. (See also global warming.)

Types of climates

Because climate depends on so many factors, no two places on Earth can be said to have exactly the same climate. Scientists, however, sort through the great amount of climate information gathered throughout the world. They look for patterns and similarities. Their findings have helped them come up with ways to classify the climates of regions throughout the world.

One method of classifying climates uses five broad groups: tropical, subtropical, cyclonic, polar, and highland climates. Each group may be further divided as well.

Tropical climates are warm all year and have no winter. They can be found in the regions near the equator. Some tropical climates, such as tropical rain forests, have a lot of rain. These are the areas closest to the equator. Further north or south of the equator are semidry regions and eventually deserts.

Subtropical climates lie between 20° and 40° latitude. They have a greater range of daily and seasonal temperatures than tropical climates. The Mediterranean climate is known for warm, dry summers and mild, wet winters. Humid subtropical climates have moderate amounts of precipitation throughout the year.

Cyclonic climates are found mostly in the Northern Hemisphere, or the lands north of the equator. These climates are ruled by the conflict between cold polar and warm tropical air masses. As a result, rain and snow are quite common in certain cyclonic climates. A wide range of temperatures from the summer to the winter seasons is another common feature of these climates.

Places with a polar climate have long, cold winters. Some areas hardly ever go above freezing. Some places always have snow and ice. Others always have a layer of frost, called permafrost, below the soil.

Highland climates have a great range of temperature between day and night. They tend to be humid, but precipitation varies by location. Highland climates are generally cooler than those of the lowlands that are at the same latitude.

Except in unusual situations due to mountain ranges or coastlines, most things that affect the climate tend to change slowly over distance. As a result, it is hard to pick up on differences in the climates of places that are near one another.