World Geography

ALC GEOGRAPHY
Climates of the Earth

*Today we are going to talk about climate and weather, and there’s a difference. Weather is the condition of the atmosphere at a given point in space and time—e.g. ‘it’s raining’ or ‘it’s sunny.’ Climate is the typical weather pattern for an area over a long period of time: Seattle is in a Marine West Coast climatic region, so it rains there often, while Arizona has a mixture of steppe and desert climates, and is typically sunny and dry.

*Climate patterns result primarily from the Earth’s relationship with the Sun.

*The axis on which the Earth rotates is tilted at an angle of about 23½ degrees compared to the plane of Earth’s revolution around the Sun. Therefore, not all parts of Earth receive equal amounts of sunlight all the time. (DRAW THE EARTH ON THE BOARD!)

*Students should turn to page 46.

*The Earth’s tilt is always in the same direction, so as the Earth revolves around the sun, different parts of the Earth are tilted towards or away from the Sun at different times of year, and the angle at which they face the Sun also varies.

*The equator, being at the mid-point between North and South, receives the most sunlight and the most direct sunlight. It is also the dividing point between the Northern and Southern Hemispheres, in which the seasons are always reversed.

*The sun is directly over the Equator on the equinoxes (the first days of spring and fall); at this time, all around the world, every place receives 12 hours of daylight and 12 hours of darkness—which is why equinox means ‘equal night.’ After that, as the Earth continues to revolve around the sun, the sun will appear directly overhead at other spots, North or South of the Equator, depending on which end of the world is experiencing summer.

*When one pole (or the other) is as close as it gets to the Sun, that is a solstice—the summer solstice for that hemisphere and the first day of winter for the other hemisphere. At this point, the Sun will be directly over one of the tropic lines. The northern tropic is the Tropic of Cancer, at 23½° North latitude. The southern one is the Tropic of Capricorn, at 23½° South latitude. Because that is as far north as the sun gets, from the point of view of anyone north of the tropics, the Sun always seems to be in the South (which is why moss grows on the south side of trees).

*Because the tropics are close to the Equator, and have low numbers of longitude, they are called the Low Latitudes.

*Because of the earth’s tilt, the farther one is away from the tropics, the less direct the sun’s light is—and the less heat it can provide. If one gets far enough away, the sun is actually invisible for part of the year. At the North and South poles, the sun is hidden by the rest of the Earth for half the year, during the fall and winter of that hemisphere’s year—but in the spring and summer, day lasts 24 hours, too.

*The Arctic circle (and the Antarctic) are the opposite of the tropics in many ways. They are the lines above which it is possible for there to be no sun at some point in the year. The are 66½° North and South, and on the lines, there is no sun on the winter solstice for the hemisphere; the farther north or south beyond the line one gets, the more nights last all day. On the other hand, on the summer solstice, it is day for 24 hours.

*Because the Artic and Antarctic are far from the Equator, and close to 90° North or South, they have high numbers in their co-ordinates, and are known as the High Latitudes.

*The areas between the Tropics and the Artic/Antarctic are known as the Mid-Latitudes.

*The air flowing on the Earth’s surface is also affected by the rotation of the Earth. As the Earth turns, air above the surface and water on the surface try to stay where they are, and so seem to be moving in the opposite direction from the spinning earth. This is known as the Coriolis effect, and results in wind and water currents tending clockwise in the North and counter-clockwise in the South, although many things can effect this on a small scale. Still, this means that the tropical and polar winds tend to blow west and the mid-latitude winds tend to blow east.

*We name winds after the direction FROM which they blow, the mid-latitude winds are called Westerlies and the polar winds are called Easterlies.

*At the equator and about 30° North or South, there is not much wind blowing across the surface. This was disastrous in sailing days.

*The zone of little or no wind near the equator was called the doldrums—a name that came from the low spirits sailors found themselves in when there was no wind or progress.

*A similar zone between about 30-35° North or South is known as the Horse Latitudes, because when ships were stranded there, they supposedly threw their horses overboard to save food and water, or killed the horses for meat.

*Ocean currents work much the same way as the winds, as the sun heats the ocean water, causing it to rise or sink, and the Coriolis effect causes it to slowly turn.

*Ocean currents affect the temperature of land near them.

*The Gulf Stream, for example, carries warm water from the Gulf of Mexico to Britain and Northern Europe, so that although England is farther north than New York, it gets far less snow.

*The currents of the oceans and winds do a great deal to create weather. Warm air creates areas of low pressure (and usually good weather), while cool air exists in areas of high pressure (often with wet weather). When two fronts meet, the cool air causes moisture in the warm air to condense, so precipitation occurs most often where fronts collide, as does more exciting weather like tornadoes and hurricanes.

*Another consideration is the fact that land heats up more quickly than water does, but it also cools down more quickly. This means that weather changes more rapidly and at greater extremes over land than over or near water. Being near water moderates the temperature, which is known as the maritime effect.

*Elevation also effects climate, as higher places are generally cooler than lowlands, and mountain areas can create rain forests and rain shadows.

*The most generally used climate classification system is that devised by Vladimir Koeppen around 1900. It divides climates into five major groups: tropical, arid, temperate, continental (cool, but not cold), and polar, with an additional classification for highland areas that can have wide variation in local climates. The Glencoe textbook largely follows this scheme, although they group the temperate and continental climates together.

*The class will fill out climate worksheets. They may work together (using pages 52-56) to find some places where each climate is found, to learn what kind of weather each region has in the winter and summer, to discover what kind of plants normally grow there, and to see what people tend to do for a living there (using page 64).

World Geography Name_____________________

Climatic Regions Chart Pages 52-56, 64

Climatic Region	Example Places	Weather & Seasonality	Natural Vegetation	Economic Activity (p.64)
Tropical Rain Forest
Tropical Savanna
Desert
Steppe
Marine West Coast
Mediterranean
Humid Subtropical
Humid Continental
Subarctic
Tundra
Ice Cap
Highlands