Earth’s Climate Zones

(refer to Fig 8.4 in your text)

During the past few weeks we have examined a number of factors, which influence climate:

  1. amount of solar energy received (related to latitude)
  2. amount of cooling related to elevation
  3. amount of precipitation (related to latitude or rainshadow)
  4. amount and rate of solar energy absorption (land vs. water; continentality)
  5. direction from which the wind blows
These factors, combined with global atmospheric circulation patterns create specific climate zones. There are 6 major climate zones, classified by the Koeppen System.

Type A - Tropical Climate

This zone covers a very large portion of the Earth’s surface, and is characterized by warm, very humid climate with small variations in seasonal temperature or length of day. Tropical rainforests are found in this zone. Constant state of high humidity is caused by atmospheric upwelling along equator (related to high influx of solar radiation). The upwelling leads to adiabatic cooling, increase in Relative Humidity, and high precipitation throughout this zone.

Type B - Dry and semi-arid Climates

This covers the largest portion of the Earth’s surface of any climate zone. Dry climates are defined as regions where potential evaporation exceeds precipitation. These zones are most commonly located between 20° and 30° latitude, on the downdraft side of the convection cell (Hadley cell) which welled up along the equator. Other deserts may be located in a rainshadow or a long distance from the ocean. This category is based on precipitation rather than on temperature, although the extremely cold polar deserts are separated out into Type E.

Type C – Mesothermal: Humid middle-latitude climate with mild winters

Many major cities are located in this climate zone. Much less extreme than zones A or B, this climate zone has distinct seasons, but relatively small seasonal temperature variations and generally moderately high rainfall. Deciduous forest and abundant flowering plants characterize this zone. Often located along coastlines where the influence of the ocean can moderate seasonal temperature changes.

Type D – Microthermal: Humid middle-latitude climate with severe winters

Large seasonal temperature variations characterize this climate zone. Harsh winters and relatively short growing season restrict agricultural productivity although cereal crops are common. Conifer forests are often lush and logging may be economically important. Usually located in the interior of a continent, far from the temperature moderating effects of oceans. This climate zone is usually above 40° latitude.

Type E - Polar

Extreme seasonal variations in amount of solar energy received (hours of daylight) and generally cold temperatures distinguish this climate zone. Few people live in this region. Even though there is little precipitation, the low level of evaporation (cold air holds very little moisture) keeps many of these areas officially classified as somewhat humid. This climate zone encompasses much of the tundra regions of the northern continents as well as the poles themselves. Grasses and dwarf shrubs are the dominant vegetation in this treeless region.

Type H - Highland (Mountain)

High altitudes cause low atmospheric pressures, generally low temperatures and low humidity. These may occur at any latitude with elevation rather than location being the main climatic control.