Earth Science 21.2 World Climates World Climates Earth Science 21.2 World Climates If you were to travel around the world , you would find an incredible variety of climates. So many climates in fact, that one might find it hard to conceive that they could all occur on one planet. Despite this diversity, climates can be classified according to their average temperatures, and amounts of precipitation. In this lesson, we will examine the Koppen climate classification system. Earth Science 21.2 World Climates The Koppen Climate Classification System: Many classification systems have been used to classify climates. Perhaps the best known and most commonly used system is the Koppen Climate Classification System. The Koppen climate classification system uses mean monthly and annual values of temperature and precipitation to classify climates. This system is often used because it classifies the world into climatic regions in a realistic way. Earth Science 21.2 World Climates The Koppen system has five principal groups Humid tropical climates Dry climates Humid mid-latitude climates Polar climates highland climates All of these groups, except those classified as dry, are defined on the basis of temperature. Dry climates are classified partly according to the amount of precipitation that falls over an area. Each of these five major groups is than subdivided further. Earth Science 21.2 World Climates Humid Tropical Climates Humid tropical climates are climates without winters. Every month in such a climate has a mean temperature above 18 degrees Celsius. There are two types of tropical climates ○ Wet tropical climates ○ Dry tropical climates Earth Science 21.2 World Climates Wet Tropical Climates The tropical rain forests of Costa Rica are typical of a wet tropical climate. Wet tropical climates have high temperatures and much annual precipitation. Recall what we have already learned about how latitude effects climate. The intensity of the sun’s rays in the tropics is consistently high. Because the sun is directly overhead much of the time, changes in the length of daylight throughout the year are very slight. Earth Science 21.2 World Climates Wet Tropical Climates The wind that blows over the tropics cause the warm, humid, unstable air to rise, cool, condense, and fall as precipitation. Note that these areas of wet tropical climates fall on a belt centered on the equator when one looks at a world climate map. Earth Science 21.2 World Climates Tropical Wet and Dry Climates: Bordering the wet tropics are climates classified as tropical wet and dry climates. Tropical wet and dry climates have temperatures and total precipitations similar to those in the wet tropics , but experience distinct dry seasons (periods of no or little rain). Savannas, which are tropical grasslands with drought resistant trees, are typical of tropical wet and dry climates. An African savanna can be seen at right. Earth Science 21.2 World Climates Humid Mid-latitude climates: Humid mid-latitude climates fall into two groups: Climates with mild winters Climates with severe winters Climates with mild winters have an average temperature in the coldest month that is below 18 degrees Celsius but above -3 C. Climates with severe winters have an average temperature in the coldest month that is below -3C. Earth Science 21.2 World Climates Humid Mid-latitude climates: There are three types of humid mid-latitude climates: Humid subtropical Marine west coast climates Dry-summer subtropical climates Earth Science 21.2 World Climates Located between 25 degrees and 40 degrees latitude on the eastern sides of continents are the humid subtropical climates. Notice that a humid subtropical climate dominates the southeastern side of the United States. In the summer, these areas experience hot, humid weather as daytime temperatures often soar. Although winters here are generally mild, frosts are common in the higher latitude areas. The temperatures and precipitation data in the graph at right are typical of a subtropical climate. Earth Science 21.2 World Climates Coastal areas between about 40 degrees and 65 degrees north and south latitude have marine west coast climates. Maritime air masses over these regions result in milder winters and cool summers with an ample amount of rainfall throughout the year. In North America, the marine west coast climate extends as a narrow belt from northernmost California into southern Alaska. The data table at right for Vancouver shows average temperature (in red) and precipitation (in blue) amounts for this zone. Earth Science 21.2 World Climates Regions with dry-summer subtropical climates are generally located between 30 degrees and 45 degrees latitude. These climatic regions are unique because they are the only humid climate that has a strong winter rainfall maximum. In the United States, dry summer subtropical climate is found only in California. It is sometimes referred to as a Mediterranean climate. Earth Science 21.2 World Climates Humid Mid-latitude with severe winters: There are two types of humid midlatitude climates with severe winters: the humid continental climates and the subarctic climates. Continental landmasses strongly influence both of these climates. As a result, both of these climates are absent from the Southern Hemisphere. There, oceans dominate the mid-latitude zone. Earth Science 21.2 World Climates Humid Mid-latitude with severe winters: Looking at the map at right we can see that the winter temperatures are quite severe while the summers are warm. Note as well that precipitation is generally greater in the summer than the winter. Earth Science 21.2 World Climates Humid Mid-latitude with severe winters: North of the humid continental climate and south of the tundra is an extensive subarctic continental climate region. (show in purple) This climate zone covers a large swath of North America, stretching from western Alaska to Newfoundland in North America. Earth Science 21.2 World Climates Humid Mid-latitude with severe winters: Winters in these regions are long and bitterly cold. In contrast, summers in the subarctic areas are relatively warm but very short. The extremely cold winters and warm short summers combine to produce the highest annual temperature ranges on Earth. Earth Science 21.2 World Climates Dry Climates: A dry climate is one in which the yearly precipitation is not as great as the potential loss of water by evaporation. The dryness of a climate is not only related to the amount of rain that falls; it also is based on the amount of evaporation of water that takes place within the zone. Evaporation, in turn, is heavily linked to the temperature of an area. There are two types of dry climates: arid (desert) and semi-arid climates (steppe) . Earth Science 21.2 World Climates Dry Climates: Arid and semi-arid climates have much in common between them. In fact, the difference between them is actually very slight. The steppe is a marginal, slightly more humid variation of the desert environment. The steppe is a transition zone that isolates the desert and creates a transition between it and the more livable humid climates. Earth Science 21.2 World Climates Dry Climates: Dry climates exist as the result of the global distribution of air pressure and winds. In regions near the Tropics of Cancer and Capricorn, air is subsiding, sinking from above. When air sinks, it becomes compressed and warms. These conditions are the exact opposite of the conditions that produce rain clouds. As a result, these regions experience clear, sunny skies and dry climates with little rain. Earth Science 21.2 World Climates Dry Climates: Other dry areas of the world include the Gobi Desert in Africa, the Great Basin of North America and the Sahara desert. These arid areas are called rain shadow deserts. Some of the Earth’ driest climates occur where a cold ocean current effects the west coast of a continent. A cold current cools the air above it. This strengthens the sinking of air in the warm, dry air masses that cause deserts. The Namib desert of Africa is an example of this type of dry coastal desert. Earth Science 21.2 World Climates Polar Climates: Polar climates are those in which the mean temperature of the warmest month is below 10 degrees Celsius. Polar winters are periods of perpetual night, or nearly so. During the summer, temperatures remain cool despite the long hours of daylight. Very little precipitation falls in polar regions. Earth Science 21.2 World Climates Polar Climates: There are two types of polar climates: the tundra climate and the ice cap climate. The tundra climate is a treeless region found almost exclusively in the Northern Hemisphere. The ice cap climate does not have a single monthly mean above 0 degrees Celsius. The landscape is covered with permanent snow and ice. Ice cap climates occur in high mountain areas and in Greenland and Antarctica. Earth Science 21.2 World Climates Highland Climates: Highland climates are localized. This means they are much different from climates in nearby surrounding areas. Conditions of highland climates often vary abruptly from one place to another. Earth Science 21.2 World Climates Highland Climates: For example, southern facing slopes are warmer than north facing slopes, and air on the windward sides of mountains is wetter than air on the leeward sides of mountains. In general, highland climates are cooler and wetter than nearby areas at lower elevations.