The north and south temperate zones are regions between the Tropic of Cancer and the Arctic Circle, and the Tropic of Capricorn and the Antarctic Circle, but temperature and precipitation are influenced by factors other than latitude. The Koppen system is used to describe climates, with type C climate being the most temperate. Topography and proximity to the ocean also affect climate, with mountains decreasing temperatures and affecting precipitation, and oceans storing heat and preventing extreme temperatures. The temperate zone can be divided into oceanic and continental areas, with the former having milder climates and more rainfall. The southern temperate zone has little landmass, while the northern temperate zone contains most of the world’s population.
The north and south temperate zones are, strictly speaking, two regions of the Earth lying respectively between the Tropic of Cancer and the Arctic Circle, and the Tropic of Capricorn and the Antarctic Circle. These regions can generally be assumed to have temperate or mild climates with no temperature extremes; however, the definition is of very limited use as far as time is concerned. Temperature and precipitation are greatly influenced by factors other than latitude, such as topography and proximity to the ocean. As a result, extreme temperatures can occur within a temperate zone, and some areas outside of them have mild climates. A more useful definition is based on temperatures and rainfall throughout the year.
The Koppen system
The most commonly used method of describing climates is the Koppen classification system, which has been in use, in one form or another, for over 100 years. In this system, there are five main climate types, labeled A, B, C, D, and E. Type C climate—mild temperate or mesothermal—most closely matches what is meant by temperate. It is defined as an area with average temperatures in the warmest months above 50°F (10°C) and with the average for the coldest month between 27 and 64°F (-3 and 18°C).
Within this typology there are further subdivisions, relating to the seasonal distribution of rainfall and temperatures, and indicated with small letters. An “s” indicates dry summers; a “w”, dry winters; and an “f”, precipitation throughout the year. A third letter represents summer temperatures, with an ‘a’ indicating very hot summers, a ‘b’, moderately hot summers, and a ‘c’, relatively cool summers. A Cfb climate would therefore be temperate, with rainfall all year round, and fairly hot summers: a climate typical of northwestern Europe, for example. Using this classification system, the temperate zones fall between 40° and 60° latitude, but are subject to various geographic influences.
The effects of topography
Topography has two main effects on climate. First, average temperatures decrease with increasing altitude. Mountainous regions between the tropics and the Arctic or Antarctic regions therefore tend to have harsher climates than their latitudes would suggest.
Mountains also have a major effect on precipitation and humidity. As the relatively warm, moist air from the ocean flows inland, it can be forced up by a mountain range. As it does, it cools and the water vapor can condense into clouds and rain. Areas on the ocean side of an elevated area will therefore tend to have a mild, humid climate, while those on the other side may be very dry, as the air has lost most of its moisture. Because humidity has a moderating effect on temperature, these areas can experience much greater extremes.
The effect of the oceans
Water is relatively slow to heat up and cool down, and for this reason, oceans tend to store heat during the winter, releasing it slowly and preventing temperatures in coastal areas from dropping very low. In summer, however, they warm up slowly, so the effect of a large body of relatively cool water tends to prevent very high temperatures in areas near the coast. Areas away from the sea, such as inland continental areas, therefore tend to have much hotter summers and much colder winters.
Based on this effect, a temperate zone can often be divided into oceanic – or maritime – and continental areas. The temperate continental zone is, in fact, not very temperate for most of the year. For example, Eastern Europe largely falls under this region and is characterized by very cold winters. At the same time, the region experiences quite warm summers, which allows it to meet the temperature range requirements for this area. There are no true continental temperate zones in the Southern Hemisphere because there are no land masses large enough to allow for such temperature swings. Areas in continental regions generally do not receive much precipitation, on average receiving less than 30 inches (75 cm) of rain annually, although thunderstorms can occur.
The other major classification, with a milder climate, is the oceanic temperate zone. In most of these areas, it is relatively rare for winter temperatures to drop below freezing to 32°F (0°C). This region experiences cyclonic rainfall, often five to ten times more than a continental area. Winter rains are often accompanied by strong winds. While these cyclonic conditions are not in the same league as tropical cyclones, they can occasionally bring about severe storms that cause significant damage.
The oceanic temperate zone does not experience temperature changes on the same scale as the continental region. During the summers, temperatures generally remain moderate, only occasionally rising well above 70°C. Similarly, in most oceanic areas, even during winter, the temperature rarely drops much below 21°C.
Global distribution
Surprisingly little landmass falls within the southern temperate zone. New Zealand, part of Australia, part of Oceania, the southernmost tip of Africa and the southern part of South America are all that are included in the area. The northern temperate zone contains the majority of the world’s population, with the United States, most of China, parts of India, much of Canada, nearly all of Europe, and much of Russia.
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