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Cl imate is the average of weather conditions over a period of time, usually over several years. Climate may be local, regional, or global. In contrast, weather is the condition of the air in the atmosphere of a local environment at any moment. The locality may be as small as the place where a person is standing, or it may be as large as a region affected by a giant air mass. The weather or atmospheric conditions may be hot or cold, dry or humid, rainy or dry, windy or calm, cloudy or clear in combination.
Climate is usually defined with two measures of atmospheric conditions: temperature and precipitation. Therefore, the climate of every country, land formation, region, town, continent, or even the whole planet is defined in terms of the amount of its average precipitation and its average temperature.
The characteristic atmospheric conditions of locations on the surface of the earth define its climate. A description of the long-term weather of an area (at least 30 years) defines its climate. The description should include the general pattern of weather conditions, seasons, weather extremes of storms-tornados, hurricanes, typhoons, cyclones, or blizzards-droughts, and rains over the climatic period.
Climate is affected by a number of factors. These factors include latitude; proximity to great lakes, seas, or an ocean; prevailing winds; type of vegetation; monsoon winds; mountain ranges; and the size of continents, versus an island or an island archipelago. The climate determines whether an area is a desert, forest, savannah, jungle, or tundra. Some areas have virtually the same climate year-round, such as the high mountains of Mexico and some tropical islands, both of which are near the equator. In other places, the climate varies with the season.
Temperature and precipitation varies with the season for most places on earth. It is, therefore, necessary to specify seasonal climate. For example, the winter climate of Ontario, Canada and its summer climate are different: the winters are much colder than are the summers. While Ontario’s daily and nighttime temperatures for every month of the year could be totaled and averaged, the results would probably not be very useful. More accurate would be averaging the temperatures for each separate season, which would give its winter climate in contrast with its summer climate. The same principle is used to describe the climate of every location on earth.
The climate in different locations is directly affected by the sunlight that reaches earth. The equator has about the same amount of sunshine year round, as it is perpendicular to the sun. The rest of the earth’s surface receives varying amounts of sunlight from day to day throughout the year. This variation is a factor in the climate in different places around the world, and makes the seasons differ in their temperatures. Temperature affects winds, which bring or drive away moisture (usually from the oceans) and therefore the amount of precipitation. The variations in sunlight throughout the year make it summer in the northern hemisphere while it is winter in the southern hemisphere. Along with local conditions, sunlight variations contribute to the climate of localities and regions.
In 1900, Vladimir Koppen introduced what is now known as the Koppen Climate Classification System. It is widely used for classifying climate globally; most climate classification systems currently in use are based on it. Because climate is concerned with long-term weather patterns at the surface of the earth, Koppen organized the world’s climate areas by their patterns of vegetation and soil.
Climate Classification System
Koppen’s classification system has five major climate types that are based on the monthly and annual averages of temperature and precipitation: Moist Tropical Climates, Dry Climates, Humid MiddleLatitude Climates, Continental Climates, and Cold Climates. Moist Tropical Climates are designated with a capital A and have high temperatures almost every day as well as heavy rainfall. Dry Climates are designated with a capital B and are characterized by small amounts of rain and widely varying temperatures between night and day. This type of climate has two subtypes: semiarid (steppe) and arid (desert). The Humid Middle-Latitude Climate-designated with a capital C-is greatly influenced by land and water differences. The summers are warm and dry while the winters are cool and wet. Continental Climates are designated with a capital D and are located in the interior of large landmasses. Here, seasonal temperatures vary and precipitation is usually low. Finally, Cold Climates-designated with a capital E-are regions covered in permanent ice; these can be the polar regions, but may also be the tops of mountains. The Koppen system also used many sub-categories to classify variations in climate, which are designated with lowercase letters.
The major climate types around the world are polar, temperate maritime, Mediterranean, subtropical, desert with cold winter and hot summer, “Chinese,” equatorial, tropical maritime, tropical, desert, temperate continentals, and polar. These climates types are so widespread, they can be referred to as climate zones.
Polar climates have long, cold winters with almost no daylight. The summers are short with very long days. They are characterized by permanent snow, ice packs, freezing temperatures, and extreme weather. The angle of the sun to the north and south poles is such that the sun’s rays glance off the earth. Sunlight also has to travel through more of the atmosphere to reach the poles, which are at an angle to its rays, reducing the amount of sunlight that reaches the pole. In addition, the white ice cap reflects much of the sunlight, which adds to the lack of warmth.
Temperate maritime climates are humid yearround. The winters are not harshly cold, and the summers are warm to hot and humid. In temperate countries such as France, it is rare for the temperatures to be too hot or too cold. Moreover, the average precipitation usually varies no more than ten percent from year to year. The climate in France is complicated because it is at the junction of several climates. When the wind is from the north, the air is cool or cold and often clear, bringing a hint of polar climate. When the wind blows from the Atlantic Ocean, it brings moisture and usual rain and wind but mild temperatures. Western France has a temperate maritime climate. In general, the wind in France is westerly from the Atlantic, which gives the country a moderate and moist climate. When the wind in France is from the east, it brings a continental temperate climate. The winters in eastern France are longer and colder with more snow. In the summer, they are cooler with warm and rainy periods of thunderstorms. If the wind in France is from the south, the temperatures are usually hot and dry due to its Mediterranean climate found along its Mediterranean shores.
The Mediterranean climate, in which grapes and olives grow well, is found in Australia, California, Chile, and South Africa, as well as around the Mediterranean. The Mediterranean climate is mild and dry in summer and winter. It is wet in spring and prone to forest or brush fires in the summer. The autumn is moderate but may also be rainy. The Mediterranean climate is wet in the springtime, which causes vegetation to grow rapidly. However, the dry summer heat withers the vegetation and makes it prone to brush fires or to forest fires.
South of France and across the Mediterranean is a region of subtropical climate in North Africa. Along the Mediterranean coast, in North Africa, the Mediterranean climate soon gives way to the south to temperature increases in the subtropical climate that is usually dry.
To the south is the great Sahara Desert, which has a desert climate that is scorching hot in the day, but freezing cold at night. In winter, temperatures may be cold enough to freeze water. Cold desert climates such as that of Mongolia are cold in the winter and hot in the summer. Snow and rain occurs occasionally in winter and summer.
In contrast, across the Atlantic, the Gulf Coastal Plain of the southern United States has a moist subtropical climate that becomes more and more tropical as the equator is approached. This type of climate is sometimes referred to as a “Chinese” climate because the southeastern United States and China have mild, semi-dry winters with hot, moist summers.
The equatorial regions have in some places little change throughout the year. For example, the region of the Congo River is near the equator, where the sun shines directly overhead all year. The high moisture content and the constant temperature cause clouds year-round. However, equatorial climates have seasons that alternate between the wet season and dry season.
Tropical maritime climates are like equatorial climates because they have summer year-round. However, the rainfall pattern is different, and the trade winds moderate the temperature.
Climate varies with a number of factors besides the season or the latitude. One factor affecting climate is the elevation of an area.
Mountains and Valleys
Mountain climates are not the same as the climate of a plain. In mountain zones, altitude causes a change in temperature. Climate is vertical: the higher the altitude, the thinner the air becomes. Thin air, especially thin dry air, holds less heat than warm moist air at sea level. So severe is the climate in mountain zones that nothing survives above 23,000 feet (7,000 meters). At that altitude and above, winds are usually fierce and temperatures so low that living cells are quickly frozen. Mountain zones occur all over the earth. There are mountains in the tropics-like Mount Kilimanjaro-which are near the equator, but are snow-covered on their summits all year long. The flora of mountain climates is different from those found at lower altitudes. Alpine plants have short stems that keep them hugging the ground out of the wind. Their leaves are small and waxy to prevent water loss, and they grow slowly because they grow only on warm days.
The climate of a valley below may also vary with their direction, in terms of the way in which sunlight is available or is blocked by a mountain. For example, one side of the valley may be shaded much more than the opposite side, giving the two sides of the same valley different climates. Valley climates can also be affected by winds from the ocean or by katabatic (down-slope) winds. The cooler, heavier air on top of a mountain can plunge rapidly down its slopes, bringing cold dry air to the valley below and forming frost hollows. The cold dry air of the katabatic wind can rob the plants in its path of moisture and stunt their growth. On the other hand, katabatic winds can cause fog by sending cooler air to the valley below, where the warm moist air is chilled to the dew point. In Greenland and on the Antarctic ice caps, katabatic winds have been clocked at 150 miles (240 kilometers) per hour. In temperate zones, katabatic winds can be an aid to agriculture. In Hungary and other regions where grapes are grown, katabatic winds at night can cool the grapes and promote their development. Otherwise, the nighttime heat would hinder viticulture.
Some mountain climatic zones have anabatic winds, which move up the slopes of mountains because the warm air in the valley is a sunny slope that warms quickly, sending warm air up the mountain.
Plate tectonics is one reason for global climate changes over the geological eras. These moving plates have carried the continents through different climate zones over the eons. Volcanic eruptions can also affect the weather for long periods, creating climate changes when enormous volumes of volcanic gas and ash are blown into the atmosphere, creating nuclear winters. These changes are similar to those believed to have been caused by an enormous meteorite or asteroid that hit the earth next to the Yucatan peninsula about 65 million years ago. The nuclear winter that it produced is believed to have been responsible for the extinction of the dinosaurs as well as a great number of other species.
In the last 400,000 years, it is believed that there have been five Ice Ages. Over the last 1 million years, there have been many more periods of global freezing. During Ice Ages, the earth was on average 5 degrees F (3 degrees C) cooler. This was cold enough for glaciers to form and cover half of North America. Glaciers also covered New Zealand and the Alps in Europe. Major Ice Ages include the Gunz Ice Age, 580,000 years ago; the Mindel Ice Age, 430,000 years ago; the Riss Ice Age, 240,000 years ago; and most recently, the Wurm Ice Age, which lasted 100,000 years and ended 20,000 years ago. There have also been “little ice ages.” Between 1430 and 1850, the temperatures in northern Europe dropped enough to cause crop failure and starvation; the River Thames froze over every winter. However, there were also periods of sudden warming.
Interglacial periods have usually been shorter than glacial periods; the shortest lasted only 15,000 years. The present interglacial period has lasted about 9,000 years. In contrast, the shortest Ice Age lasted 60,000 years.
The earth’s climate is also affected by the longterm orbit of the sun. Revolving on its axis once a day and around the sun every 365 days (plus a bit more), the earth makes an ellipse. In addition, as the earth rotates, it is tilted from perpendicular by 23.5 degrees. The tilt is what makes the sun shine on the earth in varying ways so that it is heated unevenly, causing winds and seasons. The spinning earth on its axis in space is pointed in a particular position in the sky, a position that changes in a circular pattern. The pattern, which repeats itself every 26,000 years, is called precession.
A theory regarding the cause of the Ice Ages maintains that they all seem to have started and finished gradually. On the other hand, there is counterevidence from Siberia where mammoths have been found quick-frozen while chewing flowers. This suggests that the Ice Ages started catastrophically, which may have been due to a shift in the tilt of the earth.
In addition to the earth’s climate being influenced by its axial tilt, its orbit, which is affected by gravity, is a contributor. As the earth moves in 180 cycles in relation to the other planets’ gravitations, influences may affect its speed enough to affect the lengths of summer and winter.
A Complicated Process
Climate change is a complicated process. For the climate to change, a combination of events must occur. There must be changes in the ocean temperature, the amount of clouds worldwide, the extent of polar ice, the amount of sunlight striking the earth, the position of the earth’s orbit around the sun, and human activities. Human activity is the only factor that people can really control.
Clouds reflect sunlight, but they also retain heat. How much of a cooling effect by blocking sunlight and how much of a warming effect by retaining heat that clouds have is very difficult to determine. In addition, increases in moisture that the sun is evaporating over the vast oceans should lead to more clouds. However, with an increase in cloud cover, will the climate grow warmer or cooler?
Drought and winds can add dust to the atmosphere, which will block sunlight. The effect is often similar to the reflecting actions of clouds. However, if the dust includes metallic elements, it can reflect sunlight. On the other hand, it may absorb sunlight and promote climate warming. Volcanoes and great meteorites can contribute dust to the earth’s atmosphere. The eruption in 1815 of the Indonesian volcano Tambora threw enough volcanic dust into the atmosphere to cause the “year without a summer” in 1816. Thousands starved because of the crop failures that were the result of very abnormal summer weather.
The Components of the Atmosphere
The atmosphere is the envelope of gasses surrounding the earth. It comprises four layers: the troposphere, the stratosphere, the mesosphere, and the thermosphere. The term atmosphere comes from the Greek word atomos, meaning vapor. Atmospheric pressure is the weight of the air pressing against the earth at any given point. At sea level, the weight of the air is 14.7 pounds per square inch (1.03 kilograms per square centimeter) of surface. At places below sea level such as the surface of the Dead Sea, the atmospheric pressure is greater than one atmosphere. On mountaintops, the atmospheric pressure is less. This natural feature of the weight of the atmosphere at various places on the earth’s surface is an important feature in the weather and in the climate. The gases in the atmosphere contain nitrogen (78 percent), oxygen (21 percent), argon (0.01 percent), water vapor (0.04 percent), and traces of neon, helium, krypton, and hydrogen. In addition, there are traces of ozone and carbon dioxide.
Ozone is produced in the atmosphere by lightening, and, as a greenhouse gas, is important for trapping heat in the atmosphere. If the amount of ozone in the atmosphere increases then it will have a warming effect. The ozone layer, which is very high in the atmosphere at a height of 18.5 to 31 miles (30-50 kilometers), is also important because it blocks ultraviolet light, which can cause harmful burns and eye damage and can promote skin cancer.
Carbon dioxide is a colorless, odorless gas that has an indirect effect on the weather. Small changes in the amount of ozone and carbon dioxide can have significant weather effects, mainly due to the greenhouse effect.
For human activities to affect the climate, it is likely that the changes needed would be those that affect the content of the atmosphere. However, whether human-caused changes in the atmosphere can produce predictable effects is a very hotly disputed issue. For example, chlorofluorocarbons, which were widely used in aerosol sprays and as refrigerants, have been found to be destructive of the ozone in the atmosphere. Human use of fluorocarbons appears to have damaged the ozone layer by creating a hole in the layer over the South Pole, which could have a dramatic cooling effect on the earth.
In the view of many people, the climate is in crisis. It is believed that current global warming is not completely natural, and responsibility is being assigned to human activities. The use of carbon fossil fuels since the late 1700s and the beginning of the Industrial Revolution has led to enormous quantities of wood, coal, natural gas, and petroleum being burned for heating, manufacturing, transportation, and other reasons, which has increased the amount of carbon dioxide in the atmosphere. Consequently, the increased carbon dioxide levels are believed to have caused the increase in the temperature of earth’s climate-1 degree F over the last 100 years.
When fossil fuels are burned, they produce gases, the largest percentage of which are carbon dioxide. While this is a naturally occurring chemical, it is now believed to be contributing to global warming because of the greenhouse effect. Greenhouse gasses can come from sources other than just the burning of fossil fuels or wood. Methane can be produced by rice fields, garbage dumps, cattle, and pig wastes. It is 20 times stronger than carbon dioxide as a greenhouse gas.
The amounts of carbon dioxide and ozone in the atmosphere are normally relativly small. However, these gases retain energy from the sun, which keeps energy in the atmosphere. It eventually causes the surface of the earth to warm and contributes to the “greenhouse effect,” which is a natural phenomenon of the earth’s atmosphere. Without this effect, the biosphere of earth would not exist because the earth’s climate would be too cold.
One theory of global warming argues that variations in the amounts of greenhouse gases in the atmosphere contribute to global warming and global cooling. While the burning of fossil fuels increases the amount of carbon dioxide in the atmosphere, a reverse process occurs when plants lock up carbon dioxide in plant material. If enough carbon dioxide were removed from the atmosphere, global cooling and another Ice Age could occur.
Concerns over global warming are about more than temperatures. A great number of species could become extinct. In addition, melting polar ice should cause sea levels to rise, flooding port cities, and inundating vast areas of the earth. In addition, the number and severity of tropical storms could greatly increase. Moreover, humans and livestock could undergo enormous stress from the increased heat and even starve if droughts caused crop failures.
Some scientists have predicted that global warming will increase by between 2-4 degrees F (2-5 degrees C) by 2030 unless the volume of carbon dioxide is drastically reduced. Other scientists have estimated that the amount of carbon dioxide in the atmosphere has increased 30-50 percent since 1900, and that it will continue to increase unless significant reductions are made in carbon dioxide emissions.
Deforestation is an indirect contributor to the increases in carbon dioxide in the atmosphere. Plants take up carbon dioxide for use in photosynthesis, and expel oxygen. Reductions in the number of trees globally has a deleterious effect on the atmosphere.
A region’s climate is the factor that determines which plants and what animals will inhabit it. The world’s biomes are a fabric woven from climate, plants, and animals. Global warming will drastically affect these biomes, destroying species and possibly causing drastic food losses and the death of billions of people. To stop the increase in carbon dioxide in the atmosphere, reductions in fossil fuel emissions, other emissions, and deforestation will be needed.
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