Tropics

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World map with the intertropical zone highlighted in crimson World map indicating tropics and subtropics.png
World map with the intertropical zone highlighted in crimson
Areas of the world with tropical climates Koppen-Geiger Map A present.svg
Areas of the world with tropical climates

The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at 23°26′10.2″ (or 23.43616°) N and the Tropic of Capricorn in the Southern Hemisphere at 23°26′10.2″ (or 23.43616°) S. The tropics are also referred to as the tropical zone and the torrid zone (see geographical zone).

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In terms of climate, the tropics receive sunlight that is more direct than the rest of Earth and are generally hotter and wetter as they aren't affected as much by the solar seasons. The word "tropical" sometimes refers to this sort of climate in the zone rather than to the geographical zone itself. The tropical zone includes deserts and snow-capped mountains, which are not tropical in the climatic sense. The tropics are distinguished from the other climatic and biomatic regions of Earth, which are the middle latitudes and the polar regions on either side of the equatorial zone.

The tropics constitute 39.8% of Earth's surface area [1] and contain 36% of Earth's landmass. [2] As of 2014, the region was home also to 40% of the world's 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, [3] having more extreme weather events such as heatwaves and more intense storms. [4] [3] These changes in weather conditions may make certain parts of the tropics uninhabitable. [5]

Etymology

The word "tropic" comes via Latin from Ancient Greek τροπή (tropē), meaning "to turn" or "change direction". [6]

Astronomical definition

Relationship of Earth's axial tilt (e) to the tropical and polar circles: the Tropic of Cancer is a subsolar point only at the June solstice, and the Tropic of Capricorn is only at the December solstice Axial tilt vs tropical and polar circles.svg
Relationship of Earth's axial tilt (ε) to the tropical and polar circles: the Tropic of Cancer is a subsolar point only at the June solstice, and the Tropic of Capricorn is only at the December solstice

The tropics are defined as the region between the Tropic of Cancer in the Northern Hemisphere at 23°26′10.2″ (or 23.43616°) N and the Tropic of Capricorn in the Southern Hemisphere at 23°26′10.2″ (or 23.43616°) S; [8] these latitudes correspond to the axial tilt of the Earth.

The Tropic of Cancer is the Northernmost latitude from which the Sun can ever be seen directly overhead, and the Tropic of Capricorn is the Southernmost. [8] 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.

Seasons and climate

Aerial view of Bora Bora, French Polynesia Bora Bora.jpg
Aerial view of Bora Bora, French Polynesia
Tropical sunset over the sea in Kota Kinabalu, Malaysia Kota Kinabalu by Dale Preston.jpg
Tropical sunset over the sea in Kota Kinabalu, Malaysia

Many tropical areas have both a dry and a wet season. The wet season, rainy season or green season is the time of year, ranging from one or more months when most of the average annual rainfall in a region falls. [9] Areas with wet seasons are disseminated across portions of the tropics and subtropics, some even in temperate regions. [10] Under the Köppen climate classification, for tropical climates, a wet-season month is defined as one or more months where average precipitation is 60 mm (2.4 in) or more. [11] Some areas with pronounced rainy seasons see a break in rainfall during mid-season when the intertropical convergence zone or monsoon trough moves poleward of their location during the middle of the warm season; [12] Typical vegetation in these areas ranges from moist seasonal tropical forests to savannahs.

Graph showing the zonally averaged monthly precipitation. The tropics receive more precipitation than higher latitudes. The precipitation maximum, which follows the solar equator through the year, is under the rising branch of the Hadley circulation. The sub-tropical minima are under the descending branch and cause the formation of desert areas. Monthly zonal mean precipitation.png
Graph showing the zonally averaged monthly precipitation. The tropics receive more precipitation than higher latitudes. The precipitation maximum, which follows the solar equator through the year, is under the rising branch of the Hadley circulation. The sub-tropical minima are under the descending branch and cause the formation of desert areas.

When the wet season occurs during the warm season, or summer, precipitation falls mainly during the late afternoon and early evening hours. The wet season is a time when air quality improves, freshwater quality improves and vegetation grows significantly due to the wet season supplementing flora, leading to crop yields late in the season. Floods and rains cause rivers to overflow their banks, and some animals to retreat to higher ground. Soil nutrients are washed away and erosion increases. The incidence of malaria increases in areas where the rainy season coincides with high temperatures. Animals have adaptation and survival strategies for the wetter regime. The previous dry season leads to food shortages into the wet season, as the crops have yet to mature.

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" (arid or semi-arid), including the Sahara Desert, 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 Perú.

Climate change

The climate is changing in the tropics, as it is in the rest of the world. [13] The effects of steadily rising concentrations of greenhouse gases on the climate may be less obvious to tropical residents, however, because they are overlain by considerable natural variability. Much of this variability is driven by the El Niño-Southern Oscillation (ENSO). The Tropics has warmed by 0.7-0.8°C over the last century—only slightly less than the global average—but a strong El Niño made 1998 the warmest year in most areas, with no significant warming since. Climate models predict a further 1-2°C warming by 2050 and 1-4°C by 2100.

Ecosystems

Coconut palms in the warm, tropical climate of northern Brazil Pajucara.jpg
Coconut palms in the warm, tropical climate of northern Brazil

Tropical plants and animals are those species native to the tropics. Tropical ecosystems may consist of tropical rainforests, seasonal tropical forests, dry (often deciduous) forests, spiny forests, deserts, savannahs, grasslands and other habitat types. There are often wide areas of biodiversity, and species endemism present, particularly in rainforests and seasonal forests. Some examples of important biodiversity and high-endemism ecosystems are El Yunque National Forest in Puerto Rico, Costa Rican and Nicaraguan rainforests, Amazon Rainforest territories of several South American countries, Madagascar dry deciduous forests, the Waterberg Biosphere of South Africa, and eastern Madagascar rainforests. Often the soils of tropical forests are low in nutrient content, making them quite vulnerable to slash-and-burn deforestation techniques, which are sometimes an element of shifting cultivation agricultural systems.

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 Pantropic. 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, and tropical Australasian realms.

Flora

Distribution of tropical wet forests Tropical wet forests.svg
Distribution of tropical wet forests

Flora are plants found in a specific region at a specific time. Some well-known plants that are exclusively found in, originate from, or are often associated with the tropics include:

Tropicality

Tropicality refers to the image of the tropics that people from outside the tropics have of the region, ranging from critical to verging on fetishism. [14] The idea of tropicality gained renewed interest in geographical discourse when French geographer Pierre Gourou published Les Pays Tropicaux (The Tropical World in English), in the late 1940s. [15]

Jurua River in Brazil surrounded by dense tropical rainforests The Brazilian rainforests are home to uncontacted tribes to this day. Jurua River in Brazil.jpg
Juruá River in Brazil surrounded by dense tropical rainforests The Brazilian rainforests are home to uncontacted tribes to this day.

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. [16] 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. [16] 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. [17]

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'. [18]

See also

Related Research Articles

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<span class="mw-page-title-main">Temperate climate</span> Main climate class

In geography, the temperate climates of Earth occur in the middle latitudes, which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout the year and more distinct seasonal changes compared to tropical climates, where such variations are often small and usually only have precipitation differences.

<span class="mw-page-title-main">Tropic of Cancer</span> Line of northernmost latitude at which the Sun can be directly overhead

The Tropic of Cancer, which is also referred to as the Northern Tropic, is the most northerly circle of latitude on Earth at which the Sun can be directly overhead. This occurs on the June solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent. It also reaches 90 degrees below the horizon at solar midnight on the December Solstice. Using a continuously updated formula, the circle is currently 23°26′10.2″ (or 23.43616°) north of the Equator.

<span class="mw-page-title-main">Tropic of Capricorn</span> Line of southernmost latitude at which the sun can be directly overhead

The Tropic of Capricorn is the circle of latitude that contains the subsolar point at the December solstice. It is thus the southernmost latitude where the Sun can be seen directly overhead. It also reaches 90 degrees below the horizon at solar midnight on the June Solstice. Its northern equivalent is the Tropic of Cancer.

<span class="mw-page-title-main">Circle of latitude</span> Geographic notion

A circle of latitude or line of latitude on Earth is an abstract east–west small circle connecting all locations around Earth at a given latitude coordinate line.

<span class="mw-page-title-main">Tropical and subtropical moist broadleaf forests</span> Habitat type defined by the World Wide Fund for Nature

Tropical and subtropical moist broadleaf forests (TSMF), also known as tropical moist forest, is a subtropical and tropical forest habitat type defined by the World Wide Fund for Nature.

<span class="mw-page-title-main">Subtropics</span> Geographic and climate zone

The subtropical zones or subtropics are geographical and climate zones to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from 23°26′10.2″ (or 23.43616°) to approximately 35° north and south. The horse latitudes lie within this range.

<span class="mw-page-title-main">Tropical climate</span> One of the five major climate groups in the Köppen climate classification

Tropical climate is the first of the five major climate groups in the Köppen climate classification identified with the letter A. Tropical climates are defined by a monthly average temperature of 18 °C (64.4 °F) or higher in the coolest month, and feature hot temperatures all year-round. Annual precipitation is often abundant in tropical climates, and shows a seasonal rhythm but may have seasonal dryness to varying degrees. There are normally only two seasons in tropical climates, a wet season and a dry season. The annual temperature range in tropical climates is normally very small. Sunlight is intense in these climates.

<span class="mw-page-title-main">Semi-arid climate</span> Climate with precipitation below potential evapotranspiration

A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-arid climates, depending on variables such as temperature, and they give rise to different biomes.

<span class="mw-page-title-main">Middle latitudes</span> Spatial region on Earth

The middle latitudes are a spatial region on Earth located between the Tropic of Cancer to the Arctic Circle (66°33'39"), and Tropic of Capricorn (-23°26'22") to the Antarctic Circle (-66°33'39"). They include Earth's subtropical and temperate zones, which lie between the two tropics and the polar circles. Weather fronts and extratropical cyclones are usually found in this area, as well as occasional tropical cyclones or subtropical cyclones, which have traveled from their areas of formation closer to the Equator.

<span class="mw-page-title-main">Dry season</span> Yearly period of low rainfall, especially in the tropics

The dry season is a yearly period of low rainfall, especially in the tropics. The weather in the tropics is dominated by the tropical rain belt, which moves from the northern to the southern tropics and back over the course of the year. The temperate counterpart to the tropical dry season is summer or winter.

<span class="mw-page-title-main">Wet season</span> Yearly period of high rainfall

The wet season is the time of year when most of a region's average annual rainfall occurs. Generally, the season lasts at least one month. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the tropics and subtropics.

A temperate forest is a forest found between the tropical and boreal regions, located in the temperate zone. It is the second largest biome on our planet, covering 25% of the world's forest area, only behind the boreal forest, which covers about 33%. These forests cover both hemispheres at latitudes ranging from 25 to 50 degrees, wrapping the planet in a belt similar to that of the boreal forest. Due to its large size spanning several continents, there are several main types: deciduous, coniferous, mixed forest, and rainforest.

Rainfall and the tropical climate dominate the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year, roughly following the solar equator. The tropical rain belt is an area of active rain that is positioned mostly around the tropics.

<span class="mw-page-title-main">Geographical zone</span> Major regions of Earths surface demarcated by latitude

The five main latitude regions of Earth's surface comprise geographical zones, divided by the major circles of latitude. The differences between them relate to climate. They are as follows:

  1. The North Frigid Zone, between the North Pole at 90° N and the Arctic Circle at 66°33′48.7" N, covers 4.12% of Earth's surface.
  2. The North Temperate Zone, between the Arctic Circle at 66°33′48.7" N and the Tropic of Cancer at 23°26'11.3" N, covers 25.99% of Earth's surface.
  3. The Torrid Zone, between the Tropic of Cancer at 23°26'11.3" N and the Tropic of Capricorn at 23°26'11.3" S, covers 39.78% of Earth's surface.
  4. The South Temperate Zone, between the Tropic of Capricorn at 23°26'11.3" S and the Antarctic Circle at 66°33'48.7" S, covers 25.99% of Earth's surface.
  5. The South Frigid Zone, from the Antarctic Circle at 66°33'48.7" S and the South Pole at 90° S, covers 4.12% of Earth's surface.
<span class="mw-page-title-main">Paleotropical Kingdom</span> One of the Earths six floristic kingdoms

The Paleotropical Kingdom (Paleotropis) is a floristic kingdom composed of the tropical areas of Africa, Asia and Oceania, as proposed by Ronald Good and Armen Takhtajan. Part of its flora is inherited from the ancient supercontinent of Gondwana or exchanged later. These Gondwanan lineages are related to those in the Neotropical Kingdom, composed of the tropical areas of Central and South America. Flora from the Paleotropical Kingdom influenced the tropical flora of the Australian Kingdom. The kingdom is subdivided into five floristic subkingdoms according to Takhtajan and about 13 floristic regions. In this article the floristic subkingdoms and regions are given as delineated by Takhtajan.

<span class="mw-page-title-main">Tropical savanna climate</span> Climate subtype

Tropical savanna climate or tropical wet and dry climate is a tropical climate sub-type that corresponds to the Köppen climate classification categories Aw and As. The driest month has less than 60 mm (2.4 in) of precipitation and also less than mm of precipitation.

<span class="mw-page-title-main">Tropical rainforest climate</span> Type of tropical climate in which there is no dry season

A tropical rainforest climate or equatorial climate is a tropical climate sub-type usually found within 10 to 15 degrees latitude of the equator. There are some other areas at higher latitudes, such as the coast of southeast Florida, United States, and Okinawa, Japan that fall into the tropical rainforest climate category. They experience high mean annual temperatures, small temperature ranges, and rain that falls throughout the year. Regions with this climate are typically designated Af by the Köppen climate classification. A tropical rainforest climate is typically hot, very humid, and wet with no dry season.

<span class="mw-page-title-main">Climate of Africa</span> Climate of the continent

The climate of Africa is a range of climates such as the equatorial climate, the tropical wet and dry climate, the tropical monsoon climate, the semi-arid climate, the desert climate, the humid subtropical climate, and the subtropical highland climate. Temperate climates are rare across the continent except at very high elevations and along the fringes. In fact, the climate of Africa is more variable by rainfall amount than by temperatures, which are consistently high. African deserts are the sunniest and the driest parts of the continent, owing to the prevailing presence of the subtropical ridge with subsiding, hot, dry air masses. Africa holds many heat-related records: the continent has the hottest extended region year-round, the areas with the hottest summer climate, the highest sunshine duration, and more.

<span class="mw-page-title-main">Tropical vegetation</span> Vegetation in tropical latitude

Tropical vegetation is any vegetation in tropical latitudes. Plant life that occurs in climates that are warm year-round is in general more biologically diverse that in other latitudes. Some tropical areas may receive abundant rain the whole year round, but others have long dry seasons which last several months and may vary in length and intensity with geographic location. These seasonal droughts have great impact on the vegetation, such as in the Madagascar spiny forests.

References

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  2. "tropics". National Geographic Encyclopedia. National Geographic Society. 21 January 2011. Retrieved 2017-06-26.
  3. 1 2 Yang, Hu; Lohmann, Gerrit; Lu, Jian; Gowan, Evan J.; Shi, Xiaoxu; Liu, Jiping; Wang, Qiang (2020-08-27). "Tropical Expansion Driven by Poleward Advancing Midlatitude Meridional Temperature Gradients". Journal of Geophysical Research: Atmospheres. 125 (16). Bibcode:2020JGRD..12533158Y. doi: 10.1029/2020JD033158 . ISSN   2169-897X. S2CID   225274572.
  4. Zeng, Xubin; Reeves Eyre, J. E. Jack; Dixon, Ross D.; Arevalo, Jorge (2021-05-28). "Quantifying the Occurrence of Record Hot Years Through Normalized Warming Trends". Geophysical Research Letters. 48 (10). Bibcode:2021GeoRL..4891626Z. doi:10.1029/2020GL091626. ISSN   0094-8276. OSTI   1798413. S2CID   236399809.
  5. "We Have a Chance to Keep the Tropics Habitable". Gizmodo. 2021-03-08. Retrieved 2022-11-10.
  6. "tropic". Oxford learner's dictionaries.
  7. "What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle?". Ask an Astronomer. Retrieved 19 November 2022.
  8. 1 2 "Tropical zone". meteoblue. Retrieved 19 November 2022.
  9. Glossary of Meteorology (2009). Rainy season. Archived 2009-02-15 at the Wayback Machine American Meteorological Society. Retrieved on 2008-12-27.
  10. Michael Pidwirny (2008). CHAPTER 9: Introduction to the Biosphere. PhysicalGeography.net. Retrieved on 2008-12-27.
  11. "Updated world Koppen-Geiger climate classification map" (PDF).
  12. J . S. 0guntoyinbo and F. 0. Akintola (1983). Rainstorm characteristics affecting water availability for agriculture. Archived 2009-02-05 at the Wayback Machine IAHS Publication Number 140. Retrieved on 2008-12-27
  13. Intergovernmental Panel on Climate Change, ed. (2014-03-24). Climate Change 2013 – The Physical Science Basis. doi:10.1017/cbo9781107415324. ISBN   978-1-107-05799-9.
  14. "TROPICALITY | Meaning & Definition for UK English | Lexico.com". Lexico Dictionaries | English. Archived from the original on March 25, 2022. Retrieved 2022-03-25.
  15. Arnold, David. "Illusory Riches: Representations of the Tropical World, 1840-1950", p. 6. Journal of Tropical Geography
  16. 1 2 Arnold, David. "Illusory Riches: Representations of the Tropical World, 1840-1950", p. 7. Journal of Tropical Geography
  17. Menadue, Christopher B. (2017-05-30). "Trysts Tropiques: The Torrid Jungles of Science Fiction" (PDF). ETropic: Electronic Journal of Studies in the Tropics. 16 (1). doi: 10.25120/etropic.16.1.2017.3570 . ISSN   1448-2940.
  18. Arnold, David. "Illusory Riches: Representations of the Tropical World, 1840-1950", p. 13. Journal of Tropical Geography