Climate is a Key Abiotic Factor That Affects the Biosphere

Climate Climate is a key abiotic factor that affects the biosphere. KEY CONCEPT VOCABULARY climate microclimate MAIN IDEAS Climate is the prevailing weather of a region. Earth has three main climate zones. Connect to Your World Although you might sometimes check the local weather report to see if you’ll need an umbrella, you are already familiar with the general climate where you live. If you live in the Midwest, you know that winter means cold temperatures, while in the Southwest, winter temperatures are much milder. The long-term weather patterns of an area help determine which plants and animals you will find living there. MAIN IDEA Climate is the prevailing weather of a region. FIGURE 2.1 The cavity in this log provides a humid microclimate that supports the growth of mushrooms. The weather of an area may change from day to day, and even from hour to hour. In contrast, the climate is the long-term pattern of weather conditions in a region. Climate includes factors such as average temperature and precipitation and relative humidity. It also includes the seasonal variations an area experiences, such as rainy or dry seasons, cold winters, or hot summers. The key factors that shape an area’s climate include temperature, sunlight, water, and wind. Among these abiotic factors, temperature and moisture play a large role in the shaping of ecosystems. Descriptions of a specific region’s climate take these abiotic factors into consideration. For example, a specific region such as a desert may be described as hot and dry, while a rain forest may be described as warm and moist. Even within a specific region, climate conditions may vary dramatically. A microclimate is the climate of a small specific place within a larger area. A microclimate may be as small as a hole in a decaying log where mushrooms grow, as pictured in FIGURE 2.1, or as large as a city neighborhood. San Francisco, for example, is characterized by frequent fog and cool temperatures. However, not far beyond the city limits, and even within other sections of the city itself, the weather may be quite different. Microclimates can be very important to living things. The same grassy meadow, for example, may be home to both frogs and grasshoppers. The frogs may tend toward areas that are moist, often at the base of the grasses, while the grasshoppers may prefer drier sites and cling to the tops of the grass blades. Each of these locations is a microclimate. Analyze Where in a forest might you find different microclimates? MAIN IDEA Earth has three main climate zones. Scientists use average temperature and precipitation levels to categorize a region’s climate. Using this system, Earth can be divided into three main climate zones, as shown in FIGURE 2.2. These three zones are the polar, tropical, and temperate climates. The polar climate is found at the far northern and southern regions of Earth. The tropical zone surrounds the equator. The temperate zone is the wide area in between the polar and tropical zones. Influence of Sunlight What determines an area’s climate? The answer begins with the sun. The sun’s rays are most intense, and therefore hottest, on the portion of the planet that sunlight strikes most directly. Earth’s surface is heated unevenly due to its curved shape. The area of Earth that receives the most direct radiation from the sun all year is the region at and around the equator, where the tropical climate zone is found. Near the North and South poles, or polar climate zones, the sun’s rays strike Earth’s surface at a lower angle, diffusing their heat over a larger area. Earth’s tilt on its axis also plays a role in seasonal change. As Earth orbits the sun, different regions of the planet receive higher or lower amounts of sunlight. When the North Pole is at its maximum tilt away from the sun, it is winter in the Northern Hemisphere and summer in the Southern Hemisphere. When the North Pole reaches its maximum tilt toward the sun, the opposite is true. CONNECT TO SEASONS At the March and September equinoxes, both hemispheres receive equal amounts of sunlight. At the June solstice, the Northern Hemisphere enters summer and the Southern Hemisphere enters winter. The opposite is true at the December solstice. FIGURE 2.2 Climate Zones The uneven heating of Earth by the sun results in three different climate zones. POLAR CLIMATE 90° N polar temperate The polar climate zone is located in far northern and far southern reaches of the planet, where the temperature is typically cold and often below freezing. TROPICAL CLIMATE tropical The tropical climate zone, which surrounds the equator, runs from the Tropic of Cancer to the Tropic of Capricorn and is characterized by warm, moist conditions. TEMPERATE CLIMATE temperate polar Apply What is the relationship between sunlight and climate zone? The temperate climate zone is located in the broad area lying between the polar and tropical climate zones. This zone experiences summer and winter seasons of about equal length. QUICK LAB O B S E RVI N G Microclimates Determine the temperature of inside and outside areas of your school to identify different microclimates. PROBLEM Where are different microclimates in and around your school grounds? PROCEDURE 1. Identify one place inside and one place outside your school where microclimates may exist. 2. Place a thermometer at each location. Wait at least five minutes before recording the temperature. MATERIALS • thermometer • stopwatch ANALYZE AND CONCLUDE Compare the temperatures you collected with those recorded by your classmates at different locations. Western slope Eastern slope FIGURE 2.3 The western slope of the Sierra Nevada, which faces the prevailing winds, receives precipitation throughout the year. Due to the rain shadow, the eastern slope of the Sierras is much drier. Air and Water Movement When the sun heats Earth, it warms not only the land and the rocks but also the water and the air. This heating causes movements in both water and air. Warm air and warm water are less dense than cooler air and water, and therefore they rise. Because the tropics near the equator are especially warm, the warm air here rises and the cooler air from areas to the north or south moves in to take its place. As the warm air rises, it cools. Since cold air holds less moisture than warm air does, a large amount of precipitation drops as rain. This large amount of precipitation, along with warm temperatures, defines the tropical rain forest regions found near the equator. The movement of air also leads to movement in water, forming currents. The rotation of Earth, water temperatures, and salinity levels also interact to form currents. Landmasses Landmasses also shape climates. For example, areas closer to bodies of water have a different climate from areas farther away because land tends to heat and cool more quickly than water. Thus, coastal areas tend to have smaller changes in temperature than areas farther inland. Farther inland, areas experience a much larger range of seasonal high and low temperatures. Water evaporates from open bodies such as lakes or oceans faster than it does from soil or through plant transpiration. As a result, coastal sites in general have higher humidity and receive more precipitation than inland areas. Mountains may also have a large effect on an area’s climate. As warm, moist air nears a mountain, it rises and cools. This cooling of air results in precipitation on the side of the mountain range facing the wind. On the downwind side of the mountain, drier and cooler air produces a rain shadow, or area of decreased precipitation. The Sierra Nevada mountain range in California, shown in FIGURE 2.3, is one example of this phenomenon. While the western slope receives a large amount of precipitation, the Great Basin to the east of the mountains is dry. TABLE 1. AVERAGE CLIMATE IN ALBUQUERQUE, NM D A T A A N A LY S I S CONSTRUCTING COMBINATION GRAPHS Climatograms are combination graphs that represent weather data for a specific location or biome over a period of time. Refer to the Data Analysis Feature in Section 4 of the chapter Interactions in Ecosystems. 1. Graph Data Plot the average precipitation as a bar graph, and plot the average temperature as a line graph. 2. Analyze How would you describe the temperature change throughout the year in this location? 3. Identify During which month is the precipitation level lowest for this location? 4. Analyze Is there a relationship between temperature and precipitation in Albuquerque, New Mexico? If so, explain how they are related. 5. Explain What is the benefit of using a combination graph to illustrate an area’s climate? Month Precipitation (mm) Temperature (°C) January 12.4 2.1 February 11.2 5.2 March 15.5 8.9 April 12.7 13.1 May 15.2 18.2 June 16.5 23.8 July 32.3 25.8 August 43.9 24.5 September 27.2 20.6 October 25.4 14.1 November 15.7 6.9 December 12.4 2.3 Source: National Oceanic and Atmospheric Administration Adaptations to Climate Many organisms have adaptations that allow them to survive in a specific climate. The water-holding frog shown in FIGURE 2.4 is a dramatic example. It lives in the dry grasslands and deserts of inland Australia, where the rainy season comes only once a year. Dry periods can last 10 months or more. The frog survives the dry season by burrowing underground, where water evaporates more slowly. Moisture loss is further reduced by a cocoonlike structure formed from the frog’s shed skin. When rains soak the ground, the frogs crawl out of their burrows to mate, and the females lay eggs in water puddles that form in depressions along the ground. Within a matter of weeks, the eggs hatch into tadpoles, and the tadpoles develop into frogs. This frog must move through its life cycle very quickly because the water evaporates quickly once the rains end. If the tadpoles are not ready to leave the ponds, they will die. Connect Describe the climate where you live. FIGURE 2.4 Water-holding frogs crawl out of their burrows to mate during the rainy season. SELF-CHECK Online 15.2 Formative Assessment REVIEWING MAIN IDEAS CRITICAL THINKING 1. What is the difference between climate and weather? 3. Connect Where might there be microclimates in your area? 2. What are the three different climate zones, and where are they located? 4. Infer Would areas along the shores of the Great Lakes have warmer summers and colder winters than other inland areas? Explain. HMDScience.com GO ONLINE CONNECT TO NICHES 5. Would you expect an area with several microclimates to have more or fewer ecological niches? Explain your answer. Chapter 15: The Biosphere 451