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1 Page 1 of 1 Print Climate scientists have amassed data on weather patterns and climate since the 1980s. Most agree that the average surface air temperature across the globe has increased about 1.4 F (0.8 C) since then. Predictions show that warming of the planet, or global warming, will accelerate through the end of the twenty-first century. What is climate change and global warming? Climate change is a significant change in temperature, precipitation, and wind patterns that lasts for at least several decades. These changes may be difficult to notice, but there are several signs of climate change that are observable, such as heat waves, flooding, droughts, melting glaciers, and extreme weather events. Global warming refers to warming of Earth s average temperature that has occurred since the mid-1800s. It represents only one aspect of climate change. Global warming does not simply mean that the climate everywhere on Earth will become warmer. An important part of what it means is that some weather patterns will become more extreme. 1. Physical Systems How is global warming different from climate change? What are the causes of climate change? Although average global surface temperature does fluctuate due to natural causes, most climate scientists agree that human activity is a major contributing factor to recent warming of the planet. As global population and industrialization increase, a variety of human activities increase the presence of so-called greenhouse gases in Earth s atmosphere. In contrast, the greenhouse effect is a naturally occurring process in which these gases act as a blanket, trapping the sun s heat within the atmosphere. The human-produced greenhouse gases amplify the effect and increase the warming of Earth. These gases primarily carbon dioxide and methane are released into the atmosphere through the burning of fossil fuels and wood, along with some industrial processes. Agricultural practices and the decay of organic waste in landfills also contribute to greenhouse gases. 2. Physical Systems Describe two factors contributing to climate change. What are the potential impacts of climate change on people? As Earth s surface temperature warms and its climate becomes less stable, people will be affected in several ways. Melting glaciers will cause sea levels to rise, likely rendering some coastal regions and islands uninhabitable. Increased droughts, heat waves, and wildfires will affect some regions, while other areas will be impacted by severe flooding. Storms and other extreme weather events may increase in their frequency and intensity as well. As a result, people may face increased health and safety risks along with threats to their homes, cities, and critical infrastructure systems. TEKS: 11C 3. Environment and Society How will climate change affect humans? Consider water supplies, agriculture, power and transportation systems, the environment, and human health.

2 Page 1 of 3 Print Daily life on Earth is influenced by the dynamic relationship between the Earth and the sun. The amount of direct sunlight reaching Earth s surface plays an important role in affecting the temperature of different places. The Earth s rotation determines when we receive sunlight, giving us day or night. The Earth s tilt and its revolution around the sun result in the four seasons we experience. Climate and Weather How do the relationships between the Earth and the sun affect climate? There is an important difference between climate and weather. Weather is the condition of the atmosphere in one place over a short period of time, such as hours or days. For example, when you look outside the window in the morning to decide what to wear that day, you are checking the weather. Climate, on the other hand, refers to the average weather conditions as measured over many years. Climate is the reason why you decide to buy certain types of clothing to wear based on where you live. The relationship between the Earth and the sun directly affects climate. Whether the climate in a particular region is cool and wet or hot and dry is determined by many factors, the most important of which is Earth s position in relation to the sun. The sun s heat and light reach Earth as warmth and sunlight, but they do not reach all parts of Earth at the same time or with the same intensity. Earth s Tilt and Rotation An important aspect of the Earth-sun relationship is that the Earth s axis is tilted. The axis runs from the North Pole to the South Pole through the center of the planet. Currently, the Earth is tilted at about 23½. Because of the Earth s tilted axis, not all places on Earth receive the same amount of direct sunlight at the same time. For this reason, Earth s tilt affects the temperature of a particular place. Temperature is the measure of how hot or cold a place is. Temperature is measured in degrees on a set scale. The most common scales for measuring temperature are Fahrenheit ( F) and Celsius ( C). Why is it usually warmer during the day than it is during the night? This depends on which side of the planet is facing the sun. The Earth rotates on its axis, making one complete rotation every 24 hours, or one day. The Earth s rotation from west to east ensures that every part of the world receives sunlight in a predictable pattern during those 24 hours. The side of the planet not facing the sun is colder, and the side of the planet facing the sun is warmer. Earth s Revolution While the Earth rotates on its axis, it also revolves around the closest star to us, the sun. It takes the Earth one year, approximately 365 days, to complete one revolution around the sun. The Earth s revolution, combined with its tilted axis, affects the amount of sunlight that reaches different locations on the Earth at different times of the year. People who live in the Northern Hemisphere experience summer when the Northern Hemisphere is tilted toward the sun and is receiving the most direct sunlight. The seasons are reversed north and south of the Equator. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere because the Southern Hemisphere is tilted away from the sun and receives less direct sunlight. Likewise, when it is fall in the Northern Hemisphere, it is spring in the Southern Hemisphere. Twice a year (around March 21 and September 23), the direct sunlight falls on the Equator. This day is called an equinox, meaning equal night, because daytime and nighttime hours are equal. On the equinox, equal amounts of light reach the Northern and Southern Hemispheres. The two equinoxes mark the shift in seasons between winter and spring and between summer and fall. In addition to the Equator, there are two other lines of latitude that run parallel to the Equator and mark important changes in the Earth s seasons. As the Earth proceeds in its revolution around the sun, the direct rays of the sun eventually strike the Tropic of Cancer, the latitude line at 23½ N that passes through Mexico, North Africa, and India. The sun usually hits the Tropic of Cancer around June 21, bringing the longest day of sunlight to the Northern Hemisphere. This date is known as the summer solstice and marks the beginning of the summer season in the Northern Hemisphere. By about September 23, the Earth has revolved so that the direct rays of the sun hit the Equator again. This equinox marks the end of summer and the beginning of the fall season in the Northern Hemisphere. As the Earth continues in its revolution, the direct rays of the sun eventually strike the Tropic of Capricorn the latitude line at 23½ S running through South America, the southern tip of Africa, and Australia around December 22. This marks the winter solstice, bringing the shortest day of sunlight to the Northern Hemisphere and signaling the beginning of the winter season. The most dramatic variation in the amount of sunlight occurs near the Poles. For six months of the year, one Pole gets continuous sunlight while the other Pole receives none. From about March 20 to about September 23, the polar area north of the Arctic Circle (66½ N) experiences continuous daylight or twilight. The polar area south of the Antarctic Circle (66½

3 Page 2 of 3 S) experiences continuous daylight or twilight for the other six months of the year. Continuous daylight, a phenomenon also known as midnight sun, is caused by the tilt of the Earth s axis as it revolves around the sun. The Poles are very sparsely populated, so many people remain unaffected by midnight sun. However, parts of northern North America and northern Europe such as Alaska, Sweden, Denmark, Norway, Finland, and others have become popular tourist destinations particularly because of midnight sun. Contrasting What factor distinguishes weather from climate? The Greenhouse Effect What is the greenhouse effect? Even on the warmest days, only some of the sun s rays pass through the Earth s atmosphere. The atmosphere reflects some of the radiation back into space. Enough radiation reaches Earth s surface, however, to warm the air, land, and water. Once Earth s surface absorbs the radiation from the sun and is warmed, it radiates this heat energy back again into the atmosphere. Normally, the atmosphere provides just the right amount of insulation to promote life on the planet. The 50 percent of the sun s radiation that reaches the Earth is converted into infrared radiation, or heat. As shown in the infographic, clouds and greenhouse gases atmospheric gases such as water vapor, methane, and carbon dioxide (CO2) absorb the reradiated heat energy and trap it so that most of it cannot escape back into space. The atmosphere is therefore like a greenhouse. It traps enough radiation to warm the land, water, and air and help plants grow while reflecting some radiation to ensure that the Earth does not overheat. This greenhouse effect is the warming of the Earth that occurs when the sun s radiation passes through the atmosphere, is absorbed by the Earth, and is radiated as heat energy back into the atmosphere where it cannot escape into space. Without the greenhouse effect, Earth s average temperature would be below 0 F (-17 C) and life as we know it could not exist. To understand the planet s natural greenhouse effect, consider that according to the laws of physics the radiation Earth receives from the sun must be equally balanced by the heat Earth radiates back out to space. If Earth gave back less energy than it received, the planet would eventually become too warm to support life. Likewise, if Earth gave back more energy than it received, the planet would be too cold for life. The greenhouse effect is one of the fundamental facts of atmospheric science. It is real; that fact is beyond dispute. Without it, the entire surface of the ocean would be frozen solid. Life at least the kind that depends on liquid water and warmth could not survive. We owe our existence to the greenhouse effect. So why are we worried about it?... The answer is that some of the heat radiation leaks out through the atmosphere, because there is not enough water vapor, carbon dioxide, and other gases to absorb all of the IR [infrared heat radiation]. Think of the atmosphere as a leaky blanket. Richard A. Muller, from the Columbia Forum, Physics for Future Presidents, January/February 2009 Assessing How does the greenhouse effect influence Earth s surface temperature? Skills Practice After reading about the greenhouse effect, write five questions about what you have read. Exchange papers with a partner and answer each other s questions. Reviewing Vocabulary TEKS: 3A 1. Making Connections What is the relationship between weather, climate, axis, temperature, revolution, equinox, and solstice? Using Your Notes

4 Page 3 of 3 2. Discussing Using your graphic organizer, discuss how temperature is affected by the tilt of the Earth. Answering the Guiding Questions TEKS: 3A 3. Identifying Cause and Effect How do the relationships between the Earth and the sun affect climate? TEKS: 3C 4. Explaining What is the greenhouse effect? Writing Activity TEKS: 3A, 3B 5. Informative/Explanatory Write a brief essay explaining weather conditions as they are related to annual changes in Earth-sun relationships.

5 Page 1 of 3 Print The climate of a particular place may have extreme weather and temperature ranges that are caused by several geographic features. Both the latitude and the elevation of a place, along with wind and ocean currents, influence its climate. Two sides of a mountain range may also have two different climates. While one side receives more precipitation as air rises, the opposite side has drier, warmer air as air descends. Latitude, Climate, and Elevation How are climate patterns related to each zone of latitude? The Earth s annual revolution around the sun creates predictable climate patterns. These patterns correspond with bands, or zones, of latitude. The low latitude zone is between 30 S and 30 N. This zone includes the Tropic of Capricorn, the Equator, and the Tropic of Cancer. Portions of the low latitude zone receive direct rays from the sun year-round and therefore have warm to hot climates. The high latitude zone includes the Earth s polar areas, which stretch from 60 N to 90 N and from 60 S to 90 S. When either the Northern or the Southern Hemisphere is tilted toward the sun, its polar area receives nearly continuous, but indirect, sunlight. The midlatitude zone, between 30 N and 60 N in the Northern Hemisphere and between 30 S and 60 S in the Southern Hemisphere, is home to climates that have the most variable weather on Earth. The midlatitudes generally have a temperate climate, or one that varies from fairly hot to fairly cold, with dramatic seasonal weather changes. Warm/hot and cool/cold air masses move across the midlatitudes. These movements and the interactions between the different air masses affect weather in this latitude zone throughout the year. At all latitudes, elevation influences climate because of the relationship between the elevation of a place and its temperature. The Earth s atmosphere thins as altitude increases. Less dense air retains less heat. As elevation increases, temperatures decrease by about 3.5 F (1.9 C) for each 1,000 feet (305 m). This effect occurs at all latitudes. For example, in Ecuador, the city of Quito (KEE toh) is nearly on the Equator. However, Quito lies in the Andes at an elevation of more than 9,000 feet (2,743 m), so average temperatures there are more than 20 degrees cooler than in the coastal lowlands. Sunlight is bright in places with high elevation because the thinner atmosphere filters fewer rays of the sun. But even in bright sunlight, the world s highest mountains, such as the Andes, are cold and snowy. Explaining What happens to temperature as elevation increases? Winds and Ocean Currents How do winds and ocean currents affect climate? How do wind and water work together to affect weather? Air moving across the surface of the Earth is called wind. Winds occur because sunlight heats the Earth s atmosphere and surface unevenly. Warm temperatures cause air to rise and create areas of low pressure. Cool temperatures cause air to sink, which creates areas of high pressure. Air moves along the pressure gradient from areas of high pressure to low pressure, so the cool air then flows in to replace the warm rising air. These movements cause winds to distribute the sun s energy around the planet. For this reason, wind patterns are crucial to a region s climate. Ocean currents also help distribute energy around the planet. As they circulate, cold water from the polar areas moves slowly toward the Equator. These are cold ocean currents because they consist of cooler water flowing into warmer water. The opposite is also true: warm water moves away from the Equator and these are warm currents because they consist of warmer water flowing into cooler water. Patterns of Wind and Ocean Currents As winds blow because of pressure differences on Earth s surface, warm tropical air moves toward the Poles and cool polar air moves toward the Equator. This movement of air creates the global winds that blow in fairly constant patterns called prevailing winds. The direction of prevailing winds is determined by latitude and is also affected by the Earth s movement. As the Earth rotates from west to east, the paths of the global winds are deflected to the right in the Northern Hemisphere and deflected to the left in the Southern Hemisphere. This phenomenon is called the Coriolis effect and

6 Page 2 of 3 causes prevailing winds to blow diagonally rather than along strict north, south, east, or west directions. The strength of the Coriolis effect is proportional to the speed of Earth s rotation at different latitudes. Winds are generally named for the direction from which they blow, but they sometimes were given names from the early days of sailing. Named for their ability to move trading ships through the region, the prevailing winds of the low latitudes are called trade winds. They blow from the northeast toward the Equator from about latitude 30 N and from the southeast toward the Equator from about latitude 30 S. Westerlies are the prevailing winds in the midlatitudes, blowing diagonally from west to east between about 30 N and 60 N and between about 30 S and 60 S. In the high latitudes, the polar easterlies blow diagonally east to west, pushing cold air toward the midlatitudes. Near the Equator, the horizontal movement of the trade winds subsides as the warm air rises. This rising air leaves a narrow, generally windless band called the doldrums. Two other narrow bands of calm air encircle the globe just north of the Tropic of Cancer and just south of the Tropic of Capricorn. These bands result from descending, high pressure air. In the days of wind-powered sailing ships, crews feared being stranded in these windless areas. With no moving air to lift the sails, ships were stranded for weeks in the hot, still weather. Food supplies dwindled, and perishable cargoes spoiled as the ships sat, helpless and windless. To lighten the load so the ships could take advantage of the slightest breeze, sailors would toss excess cargo and supplies overboard, including livestock being carried to colonial settlements. The horse latitudes, the calm areas at the edges of the Tropics, derived their name from this practice. Just as winds move in patterns, the cold and warm ocean currents move through the ocean in patterns. Ocean currents are caused by many of the same factors that cause winds, including the Earth s rotation, changes in air pressure, and differences in water temperature. The Coriolis effect is also observed in ocean currents. Ocean currents affect climate in the coastal lands along which they flow. Cold ocean currents cool the lands they pass, while warm ocean currents bring warmer temperatures. For example, the warmer North Atlantic Current flows near western Europe. This current gives western Europe a relatively mild climate in spite of its northern latitude. Influences on Weather Wind and water work together to affect weather in an important way. Driven by temperature, condensation creates precipitation, or water falling to the Earth in the form of rain, sleet, hail, or snow. The sudden cloudburst that cools a steamy summer day is an example of how precipitation both affects and is affected by temperature. Water vapor forms in the atmosphere from evaporated surface water. The high temperature causes the air to rise. As the air rises, however, it cools and this results in condensation of the water vapor into liquid droplets, forming clouds. Further cooling causes rain to fall, which can help lower the temperature on warm days. One example of the way climate is affected by recurring events that alter weather patterns is the El Niño (ehl NEE nyoh) phenomenon. El Niño is a periodic change in the pattern of ocean currents, water temperatures, and weather in the mid- Pacific region. El Niño does not occur every year, but its frequency has increased since the 1970s. In an El Niño year, the normally low atmospheric pressure over the western Pacific is replaced by higher pressure, and the normally high pressure over the eastern Pacific drops. This reversal causes the trade winds to diminish or even to reverse direction. The change in wind pattern reverses the equatorial ocean currents, drawing warm water from near Indonesia east to Ecuador, where it spreads along the coasts of Peru and Chile. These changes in the Pacific influence climates around the world. Precipitation increases along the coasts of North and South America, making the winters warmer and increasing the risk of floods. In Southeast Asia and Australia, drought and occasional massive forest fires occur. Climates in the midlatitudes are affected as well; for example, winter rains are heavier along the west coast of the United States during El Niño years. The costs in human and economic terms, such as damaged homes and flooded crops, make learning about and preparing for an El Niño year vitally important. It rose out of the tropical Pacific in late 1997, bearing more energy than a million Hiroshima bombs. By the time it had run its course eight months later, the giant El Niño of had... killed an estimated 2,100 people, and caused at least 33 billion [U.S.] dollars in property damage. Curt Suplee, El Niño/La Niña, National Geographic Magazine, March 1999 Describing What happens to global winds at the Equator? Skills Practice Read the part of the text that explains wind and ocean currents. Then, study the map World Zones of Latitude and Wind Patterns. Work with a partner to retell what you have read by describing the wind and ocean current patterns shown on the map.

7 Page 3 of 3 Landforms and Climate How can landforms and bodies of water affect climate? While one can generalize about the climates of places located in the same latitude zones, they vary based upon the presence or absence of certain physical features. Large bodies of water, for example, are slower to heat and cool, so they tend to keep temperatures in surrounding lands moderate. Coastal lands receive the benefit of this influence and experience less changeable weather. Conversely, the interiors of the continents tend to experience extremes in seasonal temperatures. Yet another physical feature that affects the climates in the latitude zones are the mountain ranges. Increases in elevation bring decreases in temperature. This cooler air causes condensation, which falls as rain or snow, or hangs in the air as fog. As the diagram shows, mountain ranges push wind upward and, as a result, the rising air cools and releases moisture in the form of precipitation. Most of the precipitation falls on the windward side of the mountain, or the side of the mountain range facing the wind. After the precipitation is released, winds become warmer and drier as they descend on the opposite, or leeward, side of the mountains. The hot, dry air produces little precipitation in an effect known as a rain shadow. The rain shadow effect often causes dry areas and even deserts to develop on the leeward sides of mountain ranges. Discussing What happens to winds after they release precipitation? Reviewing Vocabulary 1. Describing How are prevailing winds influenced by the Coriolis effect? Using Your Notes 2. Making Connections Which of the factors from your graphic organizer do you think have the strongest effect on the climate where you live? Answering the Guiding Questions TEKS: 4A, 5A 3. Explaining How are climate patterns related to each zone of latitude? TEKS: 4A 4. Identifying Cause and Effect How do wind currents and ocean currents affect climate? TEKS: 4A 5. Evaluating How can landforms and bodies of water affect climate? Writing Activity 6. Informative/Explanatory Suppose you are on a ship sailing in the low latitudes. Write a paragraph explaining what might happen as you drift near the Equator.

8 Page 1 of 3 Print Climate patterns vary from region to region. However, factors such as wind and air pressure can create zones where a climate becomes quite dramatic. For example, most of Australia has a dry climate, but when trade winds meet during the summer months, Australia s northern coast sees intense thunderstorms. Climate Regions and Biomes How are world climates and biomes organized? Climates in the world are organized into four climate zones: tropical, dry, midlatitude, and high-latitude climates. These climates support different kinds of biomes. A biome is a major type of ecological community defined primarily by distinctive natural vegetation and animal groups. The characteristics of biomes may overlap with one another. Two main factors affect the distribution of Earth s biomes climate and terrain, or the physical characteristics of the surface of the land. The key climatic influences are precipitation and temperature. The global circulation of air, or global winds, determines where moisture-bearing air masses move. The sun s energy drives the movement of these air masses. Earth s tilt, rotation, and revolution affect the amount of direct sunlight a place receives, and therefore, the temperature of that place. These Earth-sun relationships result in the change in seasons. Similarities in climate often result in similar biomes. For example, areas that on average receive large amounts of rainfall and have warm temperatures tend to have lush, green forests. Such areas include northern South America, central Africa, and much of Southeast Asia. This rain forest biome is indicated in olive green on the world biomes map. Key terrain influences on the distribution of Earth s biomes are the distribution of landmasses and ocean basins, and the topography of the continents. The map of world biomes shows that some biomes widely distributed in the Northern Hemisphere rarely occur south of the Equator because the Southern Hemisphere does not have large landmasses at comparable latitudes. In addition, the varied topography and elevation of the landmasses disrupt any sort of regular distribution of biomes. Tropical Climates Tropical climates are found in or near low latitudes in areas otherwise referred to as the Tropics. The two most widespread kinds of tropical climate regions are wet climates and dry climates. Tropical rain forest climates have an average daily temperature of 80 F (27 C), and since the warm air is humid, or saturated with moisture, it rains almost daily. Annual rainfall averages from 50 to 260 inches (125 to 660 cm). This continual rain tends to strip the soil of nutrients. The biome in these climates are the tropical rain forests, characterized by thick vegetation that grows in layers. Tall trees form a canopy over shorter trees and bushes, and shade-loving plants grow on the completely shaded forest floor. The world s largest tropical rain forest is in the Amazon River basin. Similar climate and vegetation exist in other parts of South America, the Caribbean, Asia, and Africa. Due to the vast amount of plant food, wildlife is also abundant, and scientists estimate that more than half of all of the plant and animal species exist in the tropical rain forests. As with all biomes, plants and animals vary within a given rain forest, with differentiation often occurring. For example, trees that grow in the mountains of the Amazon rain forest do not grow in the lowlands of the same rain forest. Tropical wet/dry climates have pronounced dry and wet seasons, with high year-round temperatures. These regions, also called savannas, have fewer plants and animals than the tropical rain forest climates. One distinguishing characteristic of a tropical wet/dry climate is that sunlight is not blocked by trees and is able to reach much of the ground surface. This makes for more highly specialized plant and animal species. Tropical savannas are found in Africa, Central and South America, Asia, and Australia. Each maintains distinct types of plant and animal life. A key factor determining the types of plants and animals is the length and severity of the dry season. Dry Climates The two main types of dry climates are semi-arid (or steppe) and arid (or desert), both of which occur in low latitudes and midlatitudes. Geographers distinguish these dry climates based on the amount of rainfall and the vegetation in each. Steppes are usually located away from oceans or large bodies of water and therefore are less humid. However, they do receive an average of 10 to 30 inches (25 to 76 cm) of rainfall per year. Steppes experience warm summers and harshly cold winters. Some steppes have heavy snowfall, while others are susceptible to droughts and violent winds. Steppes are found on almost every continent and are home to a diverse variety of grasses. Deserts are extremely dry areas that receive about 10 inches (25 cm) of rainfall or less per year and support a very small amount of plant and animal life. Only plants that can live without much water and tolerate unreliable precipitation and extreme temperatures live in the desert. Deserts are usually hot and dry, although some deserts experience snowfall in the

9 Page 2 of 3 winter. In some desert areas, underground springs support an oasis, an area of lush vegetation. Temperatures tend to vary widely from day to night, as well as from season to season. Midlatitude and High-Latitude Climates The midlatitude climates include four temperate climate regions: humid subtropical, marine west coast, Mediterranean, and humid continental. Midlatitude climates experience variable weather patterns due to two conflicting air masses. Tropical air masses move from the Equator to the Poles, and polar air masses move in the opposite direction from the Poles to the Equator. Humid subtropical climates, which include the southeastern United States as well as parts of Brazil, China, Japan, Australia, and India, are characterized by short, mild winters and nearly year-round rain. The wind patterns and high pressure from nearby oceans keep humidity levels high. Vegetation consists of prairies and evergreen and deciduous forests. Coniferous trees, most of which are evergreens, have cones. Deciduous trees, most of which have broad leaves, change color and drop their leaves in autumn. Marine west coast climates, including the southern coast of Chile, parts of Australia, the British Isles, and the Pacific coast of North America, are mainly between the latitudes of about 30 N and 60 N and about 30 S and 60 S. Ocean winds bring cool summers and cool, damp winters. Abundant rainfall supports both coniferous and deciduous trees, often resulting in mixed forests. Lands surrounding the Mediterranean Sea, in addition to the southwestern coast of Australia and central California, have mild, rainy winters and hot, dry summers. The natural vegetation includes thickets of woody bushes and short trees known as Mediterranean shrubs. Geographers classify as Mediterranean any coastal midlatitude area with similar climate and vegetation. In some midlatitude regions of the Northern Hemisphere, landforms influence climate more than winds, precipitation, or ocean temperatures do. Humid continental climate regions do not experience the moderating effect of ocean winds because of their northerly continental, or inland, locations. The farther north one travels, the longer and more severe are the snowy winters, and the shorter and cooler are the summers. Vegetation is similar to that found in marine west coast areas, with evergreens outnumbering deciduous trees in the northernmost areas. In high-latitude climates, freezing temperatures are common all year because of the lack of direct sunlight. As a result, the amount and variety of vegetation is limited here. Just south of the Arctic Circle are the subarctic climate regions. Winters here are bitterly cold, and summers are short and cool. Subarctic regions have the world s widest temperature ranges. In parts of the subarctic, only a thin layer of surface soil thaws each summer. Below is permanently frozen subsoil, or permafrost. Brief summer growing seasons may support needled evergreens. Closer to the Poles are tundra climate regions. Winter darkness and bitter cold last for months, while summer has only limited warming. The layer of thawed soil is even thinner than in the subarctic. Trees cannot establish roots, so vegetation is limited to low bushes, very short grasses, mosses, and lichens (LY kuhns). Snow and ice, often more than 2 miles (3 km) thick, constantly cover the surfaces of ice cap regions. Lichens are the only form of vegetation that can survive in these areas where monthly temperatures average below freezing. Making Connections Why do high-latitude climates have limited vegetation? Climate Change What causes climates to change over time? Climate change refers to major changes in the factors used to measure climate over an extended period of time. For example, scientists have concluded that the average global temperature has increased by 1.4 F (0.8 C) over the last century. Some indicators of climate change include rising global temperatures, severe weather changes such as intense heat waves and changes in precipitation, an increase in severe weather events and rising sea levels. Scientists search for answers by studying the interrelationships among ocean temperatures, greenhouse gases, wind patterns, and cloud cover. While scientists continue to disagree about the causes of climate change, we do know that the Earth undergoes natural and predictable cycles of cooling and warming caused by factors such as solar flares and volcanic activity. However, increased global temperatures can also be attributed to greenhouse gas emissions. Burning fossil fuels releases gases that mix with water in the air, forming acids that fall in rain and snow. Acid rain can destroy forests. Fewer forests may result in climate change. The exhaust released from burning fossil fuels in automobile engines and factories is heated in the atmosphere by the sun s ultraviolet rays, forming smog, a visible chemical haze in the atmosphere. Climate change and severe weather events affect our daily lives. The extreme rains during Hurricane Katrina caused severe flooding that ruined houses and cars, caused electricity lines to come down, and led to disease-carrying

10 Page 3 of 3 mosquitoes and bacteria that endangered public health. Changes in weather patterns that lead to an excess or lack of water can have serious effects on the amount and types of food available. Warmer oceans, severe wildfires, and stronger storms drastically affect plant and animal habitats. Explaining How does the burning of fossil fuels create smog? Reviewing Vocabulary 1. Identifying Use the following three terms in one sentence that describes humid subtropical climate regions: prairie, coniferous, deciduous. Using Your Notes 2. Describing Use your graphic organizer to describe the Earth's four climate zones. Answering the Guiding Questions 3. Categorizing How are world climates organized? 4. Drawing Conclusions What causes climates to change over time? Writing Activity TEKS: 4A 5. Informative/Explanatory Write a paragraph detailing how the four major climate regions are related to the three zones of latitude.