OVERVIEW

This chapter examines air temperature, its measurement and the factors that cause it to vary through time and space.

• When net radiation is positive, the surface gains heat and temperature rises. When net radiation is negative, the surface loses heat and temperature falls.
• Air temperature measured above urban surfaces is usually higher than that over rural surfaces.
• Temperature declines with altitude at an average rate of 6.4° C/1000 m in the troposphere which extends 12 -15 km in altitude.
• The troposphere contains:
  • Most daily weather phenomena
  • Significant amounts of water vapor
  • Clouds
  • Large numbers of aerosols on which water vapor condenses to form tiny droplets
• The outer boundary of the troposphere is the tropopause.
• In the stratosphere, the absorption of ultraviolet radiation causes the temperature to increase with altitude.
• In a temperature inversion, the normal situation of air cooling with altitude is reversed and air warms with altitude.
• Yearly temperature range is greater in high latitude and continental locations and less at equatorial and coastal locations.
• The world patterns of isotherms are largely explained by latitude, coastal-interior contrasts and elevation.
• Six important points about temperature patterns are:
  • Temperatures decrease from the equator to the poles.
  • Large landmasses in the subarctic and arctic develop centers of extremely low temperatures in winter.
  • Temperatures in equatorial regions change little from January to July.
  • Isotherms make a large north-south shift from January to July over continents in the midlatitude and subarctic zones.
  • Highlands are colder than surrounding lowlands.
  • Areas of perpetual ice and snow are intensely cold.
• Five important points about temperature range are:
  • The annual temperature range increases with latitude.
  • The greatest ranges are in the subarctic and arctic zones of Asia and North America.
  • Annual range is moderately large on land in the tropical zone.
  • Annual range in coastal areas is less than the range inland at the same latitude.
  • Small temperature ranges are found near oceans in the tropical zone.
• The greenhouse gases, carbon dioxide, methane, nitrous oxides, ozone and chloroflourocarbons, absorb longwave radiation and enhance the greenhouse effect.
• The burning of fossil fuels has increased the amount of CO2 in the atmosphere by 22% in the past 100 years.
• Carbon dioxide cycles through the earth system. It is taken up by vegetation and released by decomposition or burning. It is also taken up and released by the oceans.

KEY TERMS

conduction       environmental     specific heat      
celsius scale    lapse rate        temperature        
fahrenheit       troposphere       inversion          
scale            stratosphere      isotherms          
thermistor       precipitation     temperature        
inversion        aerosols          gradients          
transpiration    mesosphere        greenhouse gases   
urban heat       thermosphere      homosphere         
island                             heterosphere       
lapse rate                                            

STUDY QUESTIONS

1. Describe the daily temperature curve. How does it relate to the daily insolation curve?
2. What is an urban heat island? How is it formed?
3. Outline the significant features of the troposphere.
4. Why does temperature begin to increase in the stratosphere?
5. How does a high elevation influence daily temperature and temperature range?
6. What is a temperature inversion?
7. Why does the land surface heat and cool more rapidly than the ocean surface?
8. How does a coastal location affect daily and annual temperature cycles?
9. What factors control air temperature patterns?
10. List six generalizations about the pattern of air temperature on the earth's surface.
11. List five generalizations about the pattern of temperature ranges on the earth's surface.
12. What is global warming?
13. What factors may be causing the changes scientist measure in the earth's temperature?
14. What impact do experts expect global warming will have?