Chapter 7 Review

1. Chapter 7 Review Raney Evans

2. Core Case & 7.1 • Different climates support different life forms. Differences in climate mainly come from long-term differences in average annual precipitation and temperature. The three major types of climate include tropical, polar and temperate. • Weather is a set of physical conditions of the lower atmosphere such as temperature, precipitation, humidity, wind speed, cloud cover, and other factors in a given area over a period of hours or days. Climate is an area’s general pattern of atmospheric conditions over periods of at least three decades and up to thousands of years. Climate varies in different parts of the earth mostly because, over long periods of time, patterns of global air circulation and ocean currents distribute heat and precipitation unevenly between the tropics and other parts of the world. Three major factors determine how air circulates in the lower atmosphere: Uneven heating of the world’s surface by the sun, rotation of the earth on its axis, and properties of air, water and land.

3. 7.1 • Prevailing winds blowing over the oceans produce mass movements of surface water called ocean currents. Water also moves vertically in the oceans as denser water sinks while less dense water rises. The ocean and the atmosphere are strongly linked in two ways: ocean currents are affected by winds in the atmosphere, and heat from the ocean affects atmospheric circulation. • Small amounts of several gases in the atmo- sphere, including water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), absorb and release heat that warms the atmosphere, thus playing a role in determining the earth’s average temperatures and its climates. Greenhouse gases allow mostly visible light and some infrared radiation and ultraviolet (UV) radiation from the sun to pass through the atmosphere. The natural warming effect of the troposphere is called the natural greenhouse effect. Human activities such as burning fossil fuels, clearing forests, and growing crops release carbon dioxide, methane, and nitrous oxide into the atmosphere. This adds carbon dioxide to the atmosphere faster than it is removed by the carbon cycle.

4. 7.1 • Heat is absorbed and released more slowly by water than by land. This creates sea breezes. Various other topographic features of the earth’s surface can create local and regional climatic conditions that differ from the general climate of some regions. When moist air blowing inland from an ocean reaches a mountain range, it is forced upward. As it rises, it cools and expands and then loses most of its moisture as rain and snow that fall on the windward slope of the mountain . Over many decades, the resulting semiarid or arid conditions on the leeward side of a high mountain create what is called the rain shadow effect. Cities can create distinct microclimates.

5. 7.2 • Differences in climate explain why one area of the earth’s land surface is a desert, another a grassland, and another a forest. The world is divided into several major biomes, large terrestrial regions, each characterized by certain types of climate and dominant plant life. The lack of vegetation, especially in tropical and polar deserts, makes them vulnerable to sandstorms driven by winds that can spread sand from one area to another. A combination of low rainfall and varying average temperatures creates tropical, temperate, and cold deserts. Tropical deserts, such as the Sahara and the Namib of Africa are hot and dry most of the year. In temperate deserts, center photo) such as the Sonoran Desert in southeastern California, southwestern Arizona, and northwestern Mexico, daytime temperatures are high in summer and low in winter and there is more precipitation than in tropical deserts. In cold deserts such as the Gobi Desert in Mongolia, vegetation is sparse.

6. 7.2 • Grasslands occur mostly in the interiors of continents in areas that are too moist for deserts to form and too dry for forests to grow. The three main types of grassland—tropical, temperate, and cold (arctic tundra)—result from combinations of low average precipitation and varying average temperatures. One type of tropical grassland, called a savanna, contains widely scattered clumps of trees such as acacia, which are covered with thorns that keep some herbivores away. Two types of temperate grasslands are the short-grass prairies and the tall-grass prairies of the mid-western and western areas of the United States and Canada. Cold grasslands, or arctic tundra (Russian for “marshy plain”), lie south of the arctic polar ice cap. One outcome of the extreme cold is the formation of permafrost, underground soil in which captured water stays frozen for more than 2 consecutive years.

7. 7.2 • Forests are lands dominated by trees. The three main types of forest—tropical, temperate, and cold (northern coniferous, or boreal)—result from combinations of varying precipitation levels and varying average temperatures. Tropical rain forests are found near the equator where hot, moisture-laden air rises and dumps its moisture. Temperate deciduous forests, grow in areas with moderate average temperatures that change significantly with the seasons. Mountains play important ecological roles. They contain the majority of the world’s forests, which are habitats for much of the planet’s terrestrial biodiversity. They often are habitats for endemic species found nowhere else on earth. Finally, mountains play a critical role in the hydro- logic cycle by serving as major storehouses of water.

8. 7.3 • According to the 2005 Millennium Ecosystem Assessment, about 62% of the world’s major terrestrial eco- systems are being degraded or used unsustainably, as the human ecological footprint gets bigger and spreads across the globe. An important concern is that if we increase the stresses on some of these biomes, such as by clearing tropical forests, they could be replaced by grasslands in many areas. To help preserve biodiversity and to slow projected climate change, many environmental scientists call for a global effort to protect the world’s remaining wild areas from development.