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The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's axial tilt; the width of the tropics (in latitude) is twice the tilt. The tropics are also referred to as the tropical zone and the torrid zone (see geographical zone).
Due to the overhead sun, the tropics insolation the most solar energy over the course of the year, and consequently have the highest temperatures on the planet. Even when not directly overhead, the sun is still close to overhead throughout the year, therefore the tropics also have the lowest seasonal variation on the planet; "winter" and "summer" lose their temperature contrast. Instead, seasons are more commonly divided by precipitation variations than by temperature variations.
The tropics maintain wide diversity of local climates, such as rain forests, monsoons, savannahs, deserts, and Alpine climate. The word "" can specifically refer to Tropical climate, rather than to the geographic region; these usages ought not be confused.
The Earth's axial tilt is currently around 23.4°, and therefore so are the latitudes of the , marking the boundary of the tropics: specifically, ±. The northern one is called the Tropic of Cancer, and the southern is the Tropic of Capricorn. As the Earth's axial tilt changes, so too do the tropical and .
The tropics constitute 39.8% of Earth's surface area and contain 36% of Earth's landmass. , the region was home also to 40% of the world's world population, and this figure was then projected to reach 50% by 2050. Because of global warming, the weather conditions of the tropics are expanding with areas in the subtropics, having more extreme weather events such as heatwaves and more intense storms. These changes in weather conditions may make certain parts of the tropics uninhabitable.
The Tropic of Cancer is the Northernmost latitude from which the Sun can ever be seen zenith, and the Tropic of Capricorn is the Southernmost. This means that the tropical zone includes everywhere on Earth which is a subsolar point at least once during the solar year. Thus the maximum latitudes of the tropics have equal distances from the equator on either side. Likewise, they approximate the angle of the Earth's axial tilt. This angle is not perfectly fixed, mainly due to the influence of the moon, but the limits of the tropics are a geographic convention, and their variance from the true latitudes is very small.
However, regions within the tropics may well not have a tropical climate. Under the Köppen climate classification, much of the area within the geographical tropics is classed not as "tropical" but as "dry" (desert climate or semi-arid), including the Sahara, the Atacama Desert and Australian Outback. Also, there are alpine tundra and snow-capped peaks, including Mauna Kea, Mount Kilimanjaro, Puncak Jaya and the Andes as far south as the northernmost parts of Chile and Peru.
In biogeography, the tropics are divided into Paleotropics (Africa, Asia and Australia) and Neotropics (Caribbean, Central America, and South America). Together, they are sometimes referred to as the Pantropical. The system of biogeographic realms differs somewhat; the Neotropical realm includes both the Neotropics and temperate South America, and the Paleotropics correspond to the Afrotropical, Indomalayan, Oceanian realm, and tropical Australasian realms.
Tropicality encompassed two major images. One, is that the tropics represent a 'Garden of Eden', a heaven on Earth, a land of rich biodiversity or a tropical paradise.Arnold, David. "Illusory Riches: Representations of the Tropical World, 1840-1950", p. 7. Journal of Tropical Geography The alternative is that the tropics consist of wild, unconquerable nature. The latter view was often discussed in old Western literature more so than the first. Evidence suggests over time that the view of the tropics as such in popular literature has been supplanted by more well-rounded and sophisticated interpretations.
Western scholars tried to theorise why tropical areas were relatively more inhospitable to human civilisations than colder regions of the Northern Hemisphere. A popular explanation focused on the differences in climate. Tropical jungles and rainforests have much more humid and hotter weather than colder and drier temperaments of the Northern Hemisphere, giving to a more diverse biosphere. This theme led some scholars to suggest that humid hot climates correlate to human populations lacking control over nature e.g. 'the wild Amazonian rainforests'.Arnold, David. "Illusory Riches: Representations of the Tropical World, 1840-1950", p. 13. Journal of Tropical Geography
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