Geologic Processes and Landforms

S.Climatic Change

T.The Greenhouse Effect

U.The Effects of Global Warming

V.What Can Be Done about Global Climate Change?

This chapter deals with the three “spheres” commonly associated with physical geography: the lithosphere, the hydrosphere, and the atmosphere.

The term lithosphere comes from the Greek word “lithos,” meaning rock. The study of the lithosphere is akin to geology insofar as geographers want to explain why places have characteristic landscape features. Geomorphology, or the study of the appearance of the earth, is of considerable interest. But in order to understand landscape patterns – those places that we call hills, mountains, plains, and plateaus – it is necessary to understand processes such as plate tectonics.

Roughly 71 percent of the earth is covered in water, mainly in the form of the world’s oceans, so it is only natural that we consider them within the context of world regional geography. In fact, the text identifies one of the eight world regions as “Oceania.” Looking at how water cycles through the environment – the hydrologic cycle – is especially critical, and oceans have the large role in that process. In addition, oceans remain an important source of food and other natural resources, but they are also contested places as nations negotiate with one another over fishing rights and oil exploration.

Weather is the atmospheric conditions occurring at any one particular place and time. Climate is the average weather of a place over an extended period of time. The key variables in weather and climate are temperature and precipitation. These phenomena, combined with surface conditions such as elevation, have strong correlations with natural vegetation patterns and with human activities on the landscape.

Precipitation is the result of processes that cool the air to the point of condensation, changing from a gaseous to a liquid or solid form and falling to the surface. Temperature is determined by a variety of factors, including elevation, latitude, and local weather patterns. The earth’s axial tilt of 23.5 degrees gives rise to the seasons, and is the most important determinant of temperature in the middle and high latitudes of both hemispheres.

Climate and biome types are closely, but not exactly, related. Areas with desert climates usually have desert shrub vegetation; tropical rain forests are usually found in the corresponding climate. Human activities have threatened many sensitive ecosystems around the world, and Conservation International has identified various “biodiversity hot spots” that deserve immediate attention for study and conservation. Many of these hot spots are located in tropical areas or on isolated islands.

There is currently a debate about the causes and effects of global warming, though a consensus is gradually emerging that human production of greenhouse gases is one of the primary causes. Efforts to curb the production and release of these gases into the air has proven to be contentious in some cases, a worrying notion to the inhabitants of island or low-elevation countries, which might be inundated by rising seawaters.

Human-caused climate change arose after the Industrial Revolution, the second major leap forward in humankind’s ability to shape the surface of the earth. The first was the Agricultural Revolution, in which people first domesticated crops and animals. With the invention of irrigation and civilization, people began to modify the earth’s surface significantly for the first time. The Industrial Revolution spread and intensified those changes around the world, while creating medical and technological advances leading to surges in worldwide human population.

Key Terms and Concepts

10. 
    The three “spheres” are the lithosphere, hydrosphere, and atmosphere. These names, like so many scientific names, are derived from the Greek words for rock, water, and vapor, respectively. Although there are specialists – geologists, oceanographers, and meteorologists – who are devoted to the study of each of these, geographers are interested in them because, taken together, they comprise the earth’s habitable environment. [p. 19]
    

11. 
    Plate tectonics is the name for a complex process that recognizes that the earth’s lithosphere is composed of many large and small plates that are in motion. It is based, in part, on the theory of continental drift initially enunciated by the German geologist Alfred Wegener in 1912. Once important consequence of plate movement is that explains the distribution of natural hazards such as earthquakes, volcanoes, and tsunamis. Plate tectonics involves two important mechanisms known as seafloor spreading and subduction, which explain the “conveyor belt” movement of the earth’s crust. [pp. 20-22]
    

12. 
    Weather is the atmospheric conditions occurring at a given time and place, while climate is the average weather of a place over a long period of time. Precipitation occurs when water vapor in the atmosphere cools to the point of condensation. Precipitation usually requires lifting air to form, and air is lifted in several ways. Moving air striking a mountain range and being forced upward results in orographic precipitation. Cyclonic or frontal precipitation is generated in traveling low-pressure cells that bring air masses with different temperature and moisture levels into contact with each other. In tropical regions or during warmer months elsewhere, air can be heated by intense sunlight and rise, which can lead to locally intense downpours and thunderstorms in a process called convectional precipitation. Aridity is often found on the lee side of mountain ranges, under persistent high-pressure cells, and in coastal deserts influenced by cold ocean currents offshore. [pp. 22-24]
    

13. 
    The Earth has thirteen major climate types and eleven major biomes. Many climates and biomes are found in similar parts of the world but do not necessarily exactly overlap. The major climate types discussed in this book are desert, semiarid / steppe, Mediterranean, topical savanna, tropical rain forest, humid subtropical, warm humid continental, cold humid continental, marine west coast, subarctic, tundra, ice cap, and undifferentiated highland. The biomes are tropical rain forest, tropical deciduous forest, Mediterranean scrub, desert and desert shrub, savanna, prairie and steppe, temperate mixed forests, coniferous forests, tundra, ice cap, and undifferentiated highland. [pp. 26-30]
    

14. 
    The various identified “biodiversity hot spots” are mainly (but not exclusively) located in tropical rainforest regions around the globe. A number of hot spots are located on islands that tend to have high biodiversity because of the effects of the islands’ isolation, and also because human pressures on islands tends to be particularly disruptive. [pp. 30-31]
    

15. 
    The world’s oceans have played, and continue to play important roles in the lives and livelihoods of humans. They are a source of food in the form of fish and shellfish. They are a source of energy in the form of oil, as evidenced by the importance of oil rigs in places like the Gulf of Mexico, in the North Sea between the United Kingdom and Norway, and off the Atlantic coast of African nations like Nigeria and Gabon. Oceans also remain important transportation corridors, particularly in our growing global economy. The over-exploitation of heretofore rich fishing grounds, pollution, ever increasing thirst for oil as known reserves dwindle, and geopolitical tensions that potentially threaten seaborne commerce threatens these important roles. [pp. 31-32]
    

16. 
    The predominant long-term effect on the atmosphere caused by human industry is the increase in greenhouse gases, which in turn is likely to contribute to global warming. Predictions about future warming vary, given the different models and assumptions used, but one study concludes that the mean global temperature will rise from 3 degrees to 11 degrees Fahrenheit above today’s global mean temperature by the year 2100. One successful international agreement to help prevent human created global environmental change was the Montreal Protocol, which banned the use of CFCs. The Kyoto Protocol, which aims to reduce the amount of carbon dioxide put into the atmosphere, has so far met with limited success because of the refusal of the United States to agree to the protocol’s terms. [pp. 32-36]
    

This chapter should enable your students to…

• 
  Gain a historical perspective on the capacity of human societies to transform environments and landscapes
  
• 
  Understand why some countries are rich and others poor and recognize the geographic distribution of wealth and poverty
  
• 
  Explain the simultaneous trends of falling population growth in the richer countries and rapid population growth worldwide
  
• 
  Explore the principles of sustainable development
  

9. 
   
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