2.2: Climate Zones

Main Climate Zones

Based on what we have learned so far about the effect of latitude, angle of insolation, and the Earth's orbit, we realize that Earth can be divided into three main Climate Zones:

• Tropical Climate (Between the Equator and 23.5° N & S): The tropics are generally defined as the region between 23.5° N & 23.5° S of the Equator. Here, the Sun is overhead or near overhead year-round, with ample sunlight and consistent conditions. These regions experience little to no temperature change between summers and winters. However, that does not mean every place in the tropics is hot and humid. Elevation from sea level also matters. Cities at higher elevations, such as Bogotá, Colombia, which lies at an altitude of 2,640 m (8,662 ft), experience much cooler temperatures than cities near sea level. Thus, instead of thinking of hot and humid conditions year-round for regions in the tropics, think of consistent temperatures throughout the year. Figure \(\PageIndex{1}\) demonstrates how temperatures vary in Iquitos, Peru, which is closer to sea-level in the tropical climate. No matter the month, the average temperature stays close to 77°F (25°C), with some diurnal variation.

Figure \(\PageIndex{1}\): Average monthly temperature in Iquitos, Peru, versus month of the year. (CC BY-NC 4.0; Climate Iquitos by Climate-Data.org) Alternative description of the image.

• Temperate Climate (Between 23.5° and 66.5° N & S): The mid-latitudes are defined as the regions between 23.5 ° and 66.5° N & S. These regions receive ample sunlight in the summer months but less in the winter months. There is some appreciable variation between summer and winter daylight hours, as well as the heat received from the Sun. Thus, these regions experience fairly moderate temperature variations throughout the year. Figure \(\PageIndex{2}\) displays monthly average temperatures for San Jose, California, in the Temperate zone. One observes that summer temperatures in San Jose are much warmer than winter temperatures.

Figure \(\PageIndex{2}\): Average monthly temperature in San Jose, CA, versus month of the year. (CC BY-NC 4.0; Climate San Jose by Climate-Data.org) Alternative description of the image.

• Polar Climate (Between 66.5° and 90° N & S): The polar regions are defined as locations that lie between 66.5° and 90° N & S. These regions experience a lot of sunlight (but at a low angle) in the summer months and almost none in the winter months. In fact, for locations above 66.5° N (the Arctic Circle) and below 66.5°S (the Antarctic Circle), there is at least one day a year where there is 24 hours of sunlight and one day a year where there is 24 hours of darkness. The number of such days with 24 hours of sunlight and darkness increases as you travel further towards the pole. Thus, these regions experience extreme temperature swings between winter and summer. Figure \(\PageIndex{3}\) displays average monthly temperatures for Tromso, Norway, in the Polar Climate Zone. One observes that the variation between summer and winter temperatures is most extreme in Tromso, compared to San Jose or Iquitos.

Figure \(\PageIndex{3}\): Average monthly temperature in Tromso, Norway, versus month of the year. (CC BY-NC 4.0; Climate Tromso by Climate-Data.org) Alternative description of the image.

Examine Figure \(\PageIndex{1}\) from a Tropical Zone, Figure \(\PageIndex{2}\) from a Temperate Zone, and Figure \(\PageIndex{3}\) from a Polar Zone to answer the following question.

16. In general, the variation in yearly temperatures, i.e., the difference between warmest monthly temperatures and coldest monthly temperatures ________ the further away from the equator you get.
    1. increases
    2. decreases
    3. does not change

A summary of the three major climate zones based on latitude and angle of insolation is shown in Figure \(\PageIndex{4}\). However, many other factors, such as elevation, proximity to the ocean, and ocean currents, must also be considered when evaluating a location’s climate. We’ll delve into those further in future investigations.

Figure \(\PageIndex{4}\): The three main climate zones are shown along with the latitudes that separate them. (CC BY-SA 3.0; CK-12 Foundation via South Redford Open Curriculum) Alternative description of the image.