Answers to the Chapter 20 Review Questions

Answers to the Chapter 20 Review Questions

1. The five parts of the climate system include the (1) atmosphere, (2) hydrosphere, (3) biosphere, (4) solid Earth, and (5) cryosphere.

2. To cope with a great diversity of information, scientists find it not only desirable but also essential to devise some means of classifying the vast array of data to be studied. Bringing order to large quantities of information not only aids comprehension and understanding but also facilitates analysis and explanation.

3. To classify a climate using the Köppen system requires knowing the location’s mean monthly and annual values of temperature and precipitation.

4. The primary factor that distinguishes Aw climates from Af and Am climates is precipitation. Aw climates have markedly seasonal rainfall, whereas Af and Am climates have year-round rainfall. In an Aw climate the rain forest gives way to the savanna, a tropical grassland with scattered drought-tolerant trees.

5. As the equatorial low advances poleward in the summer it brings the rainy season to Aw regions. Later, with the retreat of the equatorial low, the subtropical high advances into the region, causing intense drought conditions.

6. A dry climate is defined as one in which the yearly precipitation is not as great as the potential loss of water by evaporation. Thus, dryness not only is related to annual rainfall totals but is also a function of evaporation, which in turn is closely dependent on temperature. Therefore, formulas that involve several variables are used to define dry climate boundaries.

7. The existence of the dry subtropical realm is primarily the result of the prevailing global distribution of air pressure and winds.

8. Middle-latitude deserts and steppes exist principally because of their positions in the deep interiors of large landmasses far removed from the oceans, which are the ultimate source of moisture for cloud formation and precipitation.

9. In the humid subtropics (Cfa), summers are often hot and sultry, similar to those in the rainy tropics. Afternoon or evening thunderstorms occur on an average of 40 to 100 days each year, the majority during the summer months. Winter, although mild, often brings frosts and some precipitation in the form of snow that is generated along the fronts of the frequent middle-latitude cyclones that sweep over these regions.

10. In North and South America the marine west coast climate is only a slender strip along the coast because mountains block the cool maritime air from advancing inland. In Europe, no such barrier stops the air from advancing into the continent.

11. The dry-summer subtropics are transitional because during the course of a year these areas alternate between being part of the dry tropics and an extension of the humid middle latitudes. Although middle-latitude changeability characterizes the winter, tropical constancy describes the summer.

12. Humid continental climates are land-controlled climates. They are absent in the Southern Hemisphere because the middle-latitude zone is dominated by oceans.

13. Subarctic and polar climates are usually considered humid because although precipitation totals are scanty, evaporation is also limited.

14. In the large subarctic landmasses of the taiga, the extremely cold winters and relatively warm summers combine to give this region the highest annual temperature ranges on Earth.

15. During the summer months temperatures remain cool despite the long days because the Sun is so low in the sky that its oblique rays are not effective in bringing about a genuine warming.

16. Tundra climates are found in more equatorward locations, where they are associated with cooler temperatures found at higher elevations.

17. Aside from scattered occurrences in high mountain areas, ice cap (EF) climates are confined to Greenland and Antarctica.

18. The differences between the climates of Flagstaff and Phoenix are due to their general difference in elevation. Flagstaff is cooler and wetter because of its location on the Colorado Plateau, nearly 1800 meters higher than Phoenix.

19. The carbon dioxide level has been rising owing to the burning of ever-increasing quantities of fossil fuels.

20. Atmospheric models predict that temperatures will increase because additional carbon dioxide will enhance the greenhouse effect.

21. Trace gases such as methane, nitrous oxide, and certain chlorofluorocarbons that are added to the atmosphere by human activities also act to enhance the greenhouse effect.

22. Most human-generated aerosols come from the sulfur dioxide emitted during the combustion of fossil fuels and also as a consequence of burning vegetation to clear agricultural land. These aerosols serve to lower temperatures by directly reflecting sunlight back to space and by producing tiny droplets of sulfuric acid that act as cloud nuclei. The increase in cloud droplets increases the brightness of the cloud— that is, more sunlight is reflected back to space. Human-generated aerosols are generally “washed out” by precipitation in a few days or, at most, a few weeks.

23. Possible consequences of global warming include (1) significant changes in precipitation patterns, (2) rise in global mean sea level, (3) a higher frequency and intensity of hurricanes, and (4) intensified droughts and floods associated with El Niño events.

Answers to Earth System Questions

1. Af: The wet tropics are characterized by constantly high temperatures and year-round precipitation. The most luxuriant vegetation found in any climatic region, the tropical rain forest is located in this climate.

Bwh: In this arid or desert climate, yearly precipitation is not as great as the potential loss of water by evaporation. Vegetation is sparse and adjusted to the low and infrequent rainfall.

Dfc: In the subarctic climate precipitation totals are low, with a maximum occurring during the warmer summer months. Although scrawny, the spruce, fir, larch, and birch trees in the taiga represent the largest stretch of continuous forest on the surface of Earth.

ET: The tundra climate is a treeless climate found almost exclusively in the Northern Hemisphere. The amount of water vapor in the air is low, and precipitation, most abundant during the summer months, is scanty.

2. The burning of fossil fuels adds great quantities of carbon dioxide to the atmosphere. Carbon dioxide absorbs heat. Therefore, increasing levels of carbon dioxide in the atmosphere will result in warmer global temperatures. Global warming will result in a rise in sea level and a higher frequency and greater intensity of hurricanes. The effect on people who live on a beach or barrier island will include greater and more frequent flood and storm damage.

3. The atmosphere is a very complex and interactive system. Thus, when one of the systems elements is changed, there may be many possible results. For example, an increase in the atmosphere's carbon dioxide content should cause the atmosphere to warm. However, warmer temperatures will lead to increased evaporation. If the air's greater water vapor content leads to greater cloudiness, then Earth's albedo will increase (a negative feedback mechanism) and temperatures may, therefore, decline. However, clouds also absorb terrestrial radiation that would otherwise be lost from the troposphere, a positive feedback mechanism that aids heating. However, if greater cloudiness does not result, the greater water vapor content in the atmosphere will reinforce the warming trend by absorbing heat (a positive feedback mechanism).