Unit 21


Unit Overview

This unit examines ways in which climate influences human behavior and the impacts of human activities on the climate. The main sections are

  • Heat balance of the human body
  • Shelter, houses, and climate
  • Urban microclimates
  • Air pollution
  • Human activities and the global climate machine

The human body is a many-systemed organism. One of its systems¿heat balance¿involves feedback mechanisms and heat flows. The four major types of heat flows are radiant, metabolic, evaporative, and convectional. Each flow is affected, either directly or indirectly, by climate.

Climate also plays a part in determining the type of shelter most appropriate (from an energy balance perspective) for a region. An example of a major disruption of the energy balance at the local scale is the "urban heat island", which is characterized by higher temperatures within cities than temperatures in surrounding rural areas. The high levels of consumption and emission of materials and energy in urban area, in combination with the nature and the layout of urban surfaces, yields higher temperatures than would be expected in a less-developed rural area.

Air pollution¿a product of the consumption¿can disrupt climates and damage sensitive receptors (including humans). At the mesoscale, winds can distort and advect urban pollution domes, thereby producing pollution plumes. At the regional scale, winds can transport pollutants hundreds, even thousands, of miles. Human activities are also sources for greenhouse gases and particulates, both of which could possibly modify climate at multiple spatial scales. Finally, urbanization and its associated human activities can modify not only the temperature characteristics of a region but also precipitation characteristics. In general, urbanization increases precipitation totals in downwind areas.

Teaching Objectives

  • To relate our understanding of atmospheric processes to the human environment
  • To illustrate the utility of using energy balance concepts to characterize systems of the human environment
  • To focus on several of the impacts humans had, and may come to have, on our climatic environment

Glossary of Key Terms

Dust dome The characteristic shape taken by the large quantities of dust and gaseous pollutants in a city's atmosphere.
Heat-island intensity The maximum difference in temperature between neighboring urban and rural environments.
Microclimate Climate region on a localized scale.
Pollution plume When prevailing winds exceed 13 kph (8mph), dust domes begin to detach themselves from the cities they are centered over; the polluted air streams out as a plume above the downwind countryside.
Primary pollutants Gaseous or solid pollutants that come from an industrial or domestic source or the internal combustion engine of a motor vehicle.
Secondary pollutants Produced in the air by the interaction of two or more primary pollutants or from reactions with normal atmospheric constituents.

Unit Outline

  • The heat balance of the human body
    • Average body temperature fluctuates 3 to 6 degrees; body has very limited temperature range for survival
      • humans receive shortwave radiation and emit longwave radiation
      • human body converts chemical (food) energy to heat energy (metabolic energy)
      • perspiration provides heat loss
      • convectional flow can heat or cool body
  • Shelter, houses and climate
    • Climate plays a large role in the design of dwellings
  • Urban microclimates
    • About 50 percent of the world's population resides in metropolitan areas
    • Mass, energy, and heat in the city
      • cities have their own metabolism; including consumption of food, water, and fossil fuels, and production of sewage, refuse, and pollution
      • heat values produced by a city in winter equal or exceed heat available from Sun
      • greater heat produced due to burning of fossil fuels, reflection from objects, and entrapment by dust domes
    • Urban heat islands
      • can form at any time in large cities
      • micro scale variations often seen
    • Peculiarities of metropolitan climates
      • more runoff from precipitation because most areas impenetrable by water
      • winds slowed by friction from tall buildings; less efficient
      • occasional high-velocity channeled air between skyscrapers
      • dust dome provides a lot of condensation nuclei, more clouds and fog form
      • more precipitation in urban areas due to heat rising from built-up surface
  • Air Pollution
    • Primary pollutants
      • primary gaseous pollutants
        • carbon dioxide
        • water vapour
        • hydrocarbons
        • carbon monoxide
        • oxides of sulfur and nitrogen
      • primary solid pollutants
        • Iron
        • manganese
        • titanium
        • lead
        • benzene
        • nickel
        • copper
        • coal or smoke particles
    • Secondary pollutants
      • produced by interactions of primary pollutants with each other or the atmosphere
      • secondary reducing pollutants
        • sulfur dioxide ~ sulfur trioxide~ sulfuric acid
      • secondary oxidizing pollutants
        • nitrogen dioxide + sunlight = nitrogen monoxide + 0
        • O2 + O = O3 (ozone)
    • Larger-scale air pollution
      • pollution plume
  • Human activities and the global climate machine
    • Human activities can interfere with the atmosphere

Review Questions

  1. How does an urban heat island develop, and what are the consequences of this phenomenon?
  2. List several of the primary pollutants and secondary pollutants.