Climograph for Chicago, Illinois  
Peralta Colleges, Physical Geography
Rita D. Haberlin, Instructor


  1. Climate may be defined as the average condition of the weather based upon statistics collected over a period of thirty years. Climatology is the study of climate.

  3. Climate lies at the heart of physical geography. Climate influences vegetation, soils, landforms, and water resources, and many human activities as well.

  5. A climate region is a portion of the earth's surface over which the climate characteristics are similar. Boundaries between climate regions are transition zones rather than sharply defined borders.

  7. Climates are duplicated in corresponding locations on each of the continents. It is possible to logically work out a set of climate regions for a hypothetical continent astride the equator. Temperatures vary with latitude and with maritime versus continental locations. Precipitation is controlled by pressure systems, air masses, and winds.

  9. The early Greek system of climate classification used latitude to divide the world into frigid, temperate, and torrid zones. The system ignored the influence of land and sea, and the role of precipitation in climate.

  11. Mean monthly temperature and precipitation records are often the basis for climatic classification. Dr. Vladimir Koppen, a plant physiologist used both elements to draw up a climate scheme that strongly reflects vegetation. Koppen's climate map is the most widely used. Koppen recognizes five broad climate groups:
    A (tropical, rainy), B (dry), C (mild, humid), D (cold, snowy), and E (severely cold).
    Further subgroups are indicated by the addition of second and third letter codes. The San Francisco Bay Area climate is designated Csb.

  13. Climate can be summarized on a climograph that combines mean monthly precipitation and temperature statistics on a single graph. Precipitation is shown using a bar graph and temperature is shown using a line graph. (See below)

  15. Climate change has always existed. Long-term climate trends can be obtained from such indicators as tree rings, ice cores, and lake sediments. More reliable climate data is available from weather records for the past 150 years.

  17. Average global temperatures can change over a period of a decade or less. Climate changes can be attributed to the distribution of the continents, variations in atmospheric composition, the circulation of ocean currents, solar output, and changes in the Earth's orbit.

  19. Human activities have modified the earth for many years. Many of these changes affect the earth's climate. People have altered the chemistry of the environment by adding carbon dioxide and other trace gases (methane, nitrous oxide, and chlorofluorocarbons) to the atmosphere from continued combustion of fossil fuels, deforestation, and emissions from landfills and agriculture.

  21. Computer models are used to predict the nature of future climates. However, when any part of the climate system changes, scientists must consider a variety of possible impacts called climate-feedback mechanisms. A change that reinforces the initial warming such as ice melting, and then reduces the energy reflected back to space from the darker sea surface is called a positive-feedback mechanism. On the other hand, an increase in air pollution reflects more energy back to space and causes temporary cooling. This cooling offsets warming and is called a negative-feedback mechanism.

  23. Some potential consequences of global warming include:
    (a) Altering the distribution of the world's water resources and therefore the productivity of agricultural regions that depend on rivers for irrigation
    (b) Melting of glaciers and ice sheets
    (c) Rising sea level
    (d) Decreased biological diversity as plants and animals adapt to temperature changes
    (e) A change in weather patterns, such as extreme heat waves, and higher frequency and greater intensity of hurricanes and shifts in the paths of large-scale cyclonic storms



  1. Define climate and climatology.
  2. Explain why climate is so important to physical geography.
  3. Define a climate region.
  4. Explain how climates repeat themselves.
  5. Describe the basis for the Greek classification of climate. What are its limitations?
  6. What is the most widely-used climate map?
  7. Describe the data used for climate classification. Describe the five broad climate groups (A-E) in Koppen's system.
  8. What kinds of data can be used to show climate change?
  9. What natural factors cause climate change?
  10. How have human activities affected the atmosphere?
  11. Why is it difficult to predict climate change using computer models?
  12. What are some of the possible consequences of global warming? Cite specific examples.



  1. What is the most tropical continent?
  2. What climates occur within the North American continent?
  3. Why are there no cold, snowy (D) climates in the southern hemisphere?
  4. Compare and contrast the climates of San Francisco and Chicago. Explain the differences that you observe.
Climograph for Chicago, Illinois
Climograph of San Francisco, California

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This Geography Site Is Maintained By Patricia A. Kulda  Last Update July 23, 2010