View source for Tropics

{{Short description|Region of Earth surrounding the Equator}}
{{Redirect-multi|2|Tropic|Tropical}}
{{For|the 1953 film|Tropic Zone (film)}}
[[File: World map indicating tropics and subtropics.png|thumb|upright=1.5|World map with the intertropical zone highlighted in [[crimson]]]]
[[File:Koppen-Geiger Map v2 A 1991–2020.svg|thumb|upright=1.5|Areas of the world with [[tropical climate]]s. {{legend|#0000FE|[[tropical rainforest climate|Af]]}}
{{legend|#0077FF|[[tropical monsoon climate|Am]]}}
{{legend|#46A9FA|[[tropical savanna climate|Aw/As]]}}
]]

The '''tropics''' are the region of [[Earth]] surrounding the [[equator]], where the sun may shine [[Effect of Sun angle on climate|directly overhead]]. This contrasts with the [[temperate]] or [[Polar regions of Earth|polar]] regions of Earth, where the Sun can never be directly overhead. Because of [[Axial tilt#Earth|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 sun's high angle throughout the year, the tropics [[insolation|receive]] 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 [[Season#Tropical|by precipitation variations]] than by temperature variations or daylight hours.

The tropics maintain wide diversity of local climates, such as [[rain forests]], [[monsoons]], [[savannahs]], [[deserts]], and [[Alpine climate|high altitude snow-capped mountains]]. The word "[[wiktionary:tropical|tropical]]" can specifically refer to [[Tropical climate|certain kinds of weather]], rather than to the geographic region; these usages ought not be confused.

The Earth's axial tilt is [[Ecliptic#Obliquity of the ecliptic|currently around 23.4°]], and therefore so are the latitudes of the [[tropical circle]]s, marking the boundary of the tropics: specifically, ±{{Circle of latitude|Tropical|Convert}}. The northern one is called the [[Tropic of Cancer]], and the southern is the [[Tropic of Capricorn]]. As the Earth's axial tilt changes,{{Efn|text=Currently −0.013° per hundred years.}} so too do the tropical and [[polar circle]]s.

The tropics constitute 39.8% of Earth's surface area<ref>{{cite web|url=http://godplaysdice.blogspot.co.uk/2007/12/how-much-land-is-in-tropics.html|date=2007-12-04|access-date=2017-06-26|website=God Plays Dice|title=How much land is in the tropics?}}</ref> and contain 36% of Earth's [[landmass]].<ref>{{cite web |date=21 January 2011 |title=tropics |url=https://www.nationalgeographic.org/resource/tropics/ |access-date=2017-06-26 |website=National Geographic Encyclopedia |publisher=National Geographic Society}}</ref> {{as of|2014}}, the region was home also to 40% of the world's [[world population|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]],<ref name=":0">{{Cite journal |last1=Yang |first1=Hu |last2=Lohmann |first2=Gerrit |last3=Lu |first3=Jian |last4=Gowan |first4=Evan J. |last5=Shi |first5=Xiaoxu |last6=Liu |first6=Jiping |last7=Wang |first7=Qiang |date=2020-08-27 |title=Tropical Expansion Driven by Poleward Advancing Midlatitude Meridional Temperature Gradients |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=125 |issue=16 |article-number=e2020JD033158 |doi=10.1029/2020JD033158 |bibcode=2020JGRD..12533158Y |s2cid=225274572 |issn=2169-897X|doi-access=free }}</ref> having more extreme weather events such as heatwaves and more intense storms.<ref>{{Cite journal |last1=Zeng |first1=Xubin |last2=Reeves Eyre |first2=J. E. Jack |last3=Dixon |first3=Ross D. |last4=Arevalo |first4=Jorge |date=2021-05-28 |title=Quantifying the Occurrence of Record Hot Years Through Normalized Warming Trends |url=https://onlinelibrary.wiley.com/doi/10.1029/2020GL091626 |journal=Geophysical Research Letters |language=en |volume=48 |issue=10 |article-number=e2020GL091626 |doi=10.1029/2020GL091626 |bibcode=2021GeoRL..4891626Z |osti=1798413 |s2cid=236399809 |issn=0094-8276}}</ref><ref name=":0" /> These changes in weather conditions may make certain parts of the tropics uninhabitable.<ref>{{Cite web |date=2021-03-08 |title=We Have a Chance to Keep the Tropics Habitable |url=https://gizmodo.com/we-have-a-chance-to-keep-the-tropics-habitable-1846430164 |access-date=2022-11-10 |website=Gizmodo |language=en}}</ref>

== Etymology ==
The word "tropic" comes via [[Latin]] from [[Ancient Greek]] {{lang|grc|[[wikt:τροπή|τροπή]]}} ({{Transliteration|grc|tropē}}), meaning "to turn" or "change direction".<ref>{{cite web|url=https://www.oxfordlearnersdictionaries.com/definition/english/tropic|title=tropic|website=Oxford learner's dictionaries}}</ref>

== Astronomical definition ==
[[File:axial_tilt_vs_tropical_and_polar_circles.svg|thumb|350px|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]]<ref>{{cite web|url=https://curious.astro.cornell.edu/physics/160-our-solar-system/the-earth/seasons/15-what-is-the-significance-of-the-tropic-of-cancer-tropic-of-capricorn-arctic-circle-and-antarctic-circle-beginner|title=What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle?|website=Ask an Astronomer|access-date=19 November 2022}}</ref>]]

The tropics are defined as the region between the [[Tropic of Cancer]] in the [[Northern Hemisphere]] at {{Circle of latitude|Tropical|Convert}} N and the [[Tropic of Capricorn]] in the [[Southern Hemisphere]] at {{Circle of latitude|Tropical|Convert}} S;<ref name="meteo">{{cite web|url=https://content.meteoblue.com/en/research-education/educational-resources/meteoscool/general-climate-zones/tropical-zone|title=Tropical zone|website=meteoblue|access-date=19 November 2022}}</ref> these latitudes correspond to the [[axial tilt#Earth|axial tilt of the Earth]].

The Tropic of Cancer is the Northernmost latitude from which the [[Sun]] can ever be seen [[zenith|directly overhead]], and the Tropic of Capricorn is the Southernmost.<ref name="meteo" /> 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 ==
[[File:Bora Bora.jpg|thumb|Aerial view of [[Bora Bora]] in [[French Polynesia]]]]
[[File:Kota Kinabalu by Dale Preston.jpg|thumb|Tropical sunset over the sea in [[Kota Kinabalu]] in [[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.<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?id=rainy-season1 Rainy season.] {{webarchive|url=https://web.archive.org/web/20090215203023/http://amsglossary.allenpress.com/glossary/search?id=rainy-season1 |date=2009-02-15 }} American Meteorological Society. Retrieved on 2008-12-27.</ref>  Areas with wet seasons are disseminated across portions of the tropics and [[subtropics]], some even in [[Temperate climate|temperate]] regions.<ref>Michael Pidwirny (2008). [http://www.physicalgeography.net/fundamentals/9k.html CHAPTER 9: Introduction to the Biosphere.] PhysicalGeography.net. Retrieved on 2008-12-27.</ref>  Under the [[Köppen climate classification]], for [[tropical climate]]s, a wet-season month is defined as one or more months where average precipitation is {{convert|60|mm|sp=us|abbr=on}} or more.<ref>{{cite web | url=http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.pdf | title=Updated world Koppen-Geiger climate classification map | archive-url=https://web.archive.org/web/20071024063821/http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.pdf | archive-date=2007-10-24 | url-status=dead }}</ref>  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;<ref name="JS">J . S. 0guntoyinbo and F. 0. Akintola (1983). [http://www.cig.ensmp.fr/~iahs/redbooks/a140/iahs_140_0063.pdf Rainstorm characteristics affecting water availability for agriculture.] {{webarchive|url=https://web.archive.org/web/20090205200119/http://www.cig.ensmp.fr/~iahs/redbooks/a140/iahs_140_0063.pdf |date=2009-02-05 }} IAHS Publication Number 140. Retrieved on 2008-12-27</ref> Typical vegetation in these areas ranges from moist [[seasonal tropical forest]]s to [[savanna]]hs.[[File:Monthly zonal mean precipitation.png|thumb|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 (meteorology)|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" ([[desert climate|arid]] or [[semi-arid climate|semi-arid]]), including the [[Sahara|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 [[Peru]].

=== Climate change ===
{{See also|Climate change effects on tropical regions}}

The climate is changing in the tropics, as it is in the rest of the world.<ref>{{Cite book |date=2014-03-24 |editor-last=Intergovernmental Panel on Climate Change |title=Climate Change 2013 – The Physical Science Basis |url=http://dx.doi.org/10.1017/cbo9781107415324 |doi=10.1017/cbo9781107415324|isbn=978-1-107-05799-9 }}</ref> The effects of steadily rising concentrations of [[greenhouse gas]]es 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|El Niño-Southern Oscillation (ENSO)]]. The Tropics has warmed by 0.7–0.8&nbsp;°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&nbsp;°C warming by 2050 and 1–4&nbsp;°C by 2100.

== Ecosystems ==
[[File:Tropical wet forests.svg|thumb|Distribution of [[tropical wet forest]]s]]

[[Tropical plants]] and animals are those species native to the tropics. Tropical ecosystems may consist of [[tropical rainforest]]s, [[seasonal tropical forests]], [[Tropical and subtropical dry broadleaf forests|dry (often deciduous) forests]], spiny forests, [[desert]]s, savannahs, [[grassland]]s 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 Rica]]n and [[Nicaragua]]n rainforests, [[Amazon rainforest]] territories of several [[South America]]n 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 [[Paleotropical Kingdom|Paleotropics]] (Africa, Asia and Australia) and [[Neotropical realm|Neotropics]] (Caribbean, Central America, and South America). Together, they are sometimes referred to as the [[Pantropical|Pantropic]]. The system of [[biogeographic realm]]s differs somewhat; the Neotropical realm includes both the Neotropics and temperate South America, and the Paleotropics correspond to the [[Afrotropical realm|Afrotropical]], [[Indomalayan realm|Indomalayan]], [[Oceanian realm|Oceanian]], and tropical [[Australasian realm]]s.

== Flora ==
{{See also|Tropical garden}}

[[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:

* [[Bamboo]]
* [[Banana|Banana trees]]
* [[Citrus|Citrus fruits]] such as [[Orange (fruit)|oranges]], [[lemon]]s, [[Mandarin orange|mandarins]], etc.
* [[Coconut|Coconut trees]]
* [[Coffee plant|Coffee]]
* [[Dragon fruit]]
* [[Fern]]s
* [[Jackfruit]]
* [[Orchidaceae|Orchids]]
* [[Arecaceae|Palm trees]]
* [[Papaya|Papaya trees]]
* [[Rubber tree]]
* [[Stone fruits]] such as [[mango]]s, [[avocado]], [[sapote]] etc.
* [[Strelitzia|Bird of paradise flower]]
* [[Theobroma cacao|Cacao]]
* [[Victoria (plant)|Giant water lily]]

<gallery widths="200" heights="200">
File:Pajuçara.jpg|[[Coconut]] palms in the warm, tropical climate of [[Pajuçara]] in northern [[Brazil]]
File:Pitaya cross section ed2.jpg|[[Dragon fruit]], a tropical fruit from several different cacti originally from the [[Americas]]
File:Kew Gardens giant water lily.JPG|A [[Victoria (plant)|Giant Water Lily]], one of which can support up to 32 kilograms of weight
</gallery>

==Tropicality==
[[File:Juruá River in Brazil.jpg|thumb|[[Juruá River]] surrounded by the dense [[Amazon rainforest]], which is home to [[uncontacted tribes]] to this day]]

'''''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.<ref>{{Cite web |title=TROPICALITY {{!}} Meaning & Definition for UK English {{!}} Lexico.com |url=https://www.lexico.com/definition/tropicality |archive-url=https://web.archive.org/web/20220325115446/https://www.lexico.com/definition/tropicality |url-status=dead |archive-date=March 25, 2022 |access-date=2022-03-25 |website=Lexico Dictionaries {{!}} English |language=en}}</ref> 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.<ref>Arnold, David. "Illusory Riches: Representations of the Tropical World, 1840-1950", p. 6. Journal of Tropical Geography</ref>

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.<ref name="Arnold, David p. 7">Arnold, David. "Illusory Riches: Representations of the Tropical World, 1840-1950", p. 7. Journal of Tropical Geography</ref> 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.<ref name="Arnold, David p. 7"/> 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.<ref>{{Cite journal|last=Menadue|first=Christopher B.|date=2017-05-30|title=Trysts Tropiques: The Torrid Jungles of Science Fiction|journal=ETropic: Electronic Journal of Studies in the Tropics|language=en|volume=16|issue=1|doi=10.25120/etropic.16.1.2017.3570|issn=1448-2940|url=https://researchonline.jcu.edu.au/49178/1/Trysts_Tropiques.pdf|doi-access=free}}</ref>

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'.<ref>Arnold, David. "Illusory Riches: Representations of the Tropical World, 1840-1950", p. 13. ''Journal of Tropical Geography''</ref>

== See also ==
{{Portal|Geography}}
* [[Hardiness zone]]
* [[Lahaina Noon]]
* [[Tropical ecology]]
* [[Tropical marine climate]]
* [[Tropical year]]
* [[Tropical medicine]]
* [[Polar circle]]

==Notes==
{{Reflist|group=lower-alpha}}

== References ==
{{Reflist|30em}}

== External links ==
* {{Commons category-inline}}

{{Authority control}}

[[Category:Tropics| ]]
[[Category:Seasons]]