World map with the intertropical zone highlighted in red.
The
tropics, seated in the
equatorial regions of the world, are limited in
latitude by the
Tropic of Cancer in the northern hemisphere at approximately 23°26' (23.4°) N latitude and the
Tropic of Capricorn in the southern hemisphere at 23°26' (23.4°) S latitude. The tropics are also referred to as the
tropical zone and the
torrid zone (see
geographical zone).
The tropics include all the areas on The Earth where the
sun reaches a point directly overhead and a point directly underneath at least once during the solar year. In the
temperate zones, the sun never reaches the
zenith or the
nadir and is never directly overhead or directly underneath, always passing south of the
zenith in the northern hemisphere, north of the
zenith in the southern hemisphere, south of the
nadir in the southern hemisphere and north of the
nadir in the northern hemisphere.
Tropical seasons and climate
A noontime scene from the
Philippines on a day when the
sun is almost directly overhead.
The seasons in the tropics are dominated by the movement of the
tropical rain belt (or
ITCZ), which moves from the northern to the southern tropics and back over the course of a year, resulting in a
dry season and a
wet season rather than the various temperatures and day lengths indicative of the
spring,
summer,
autumn and
winter pattern found in areas outside the tropics.
However, the starting dates of the
seasons are related to the tropics, despite the fact that these dates only apply in the
temperate and
polar regions with only the
winter solstice date applying in the tropics because the
summer solstice occurs when the sun is at the
zenith, which occurs at different dates for different
latitudes. Spring begins when the sun is directly over the equator (
vernal equinox). Summer begins when the sun is directly over the
Tropic of Cancer in the north or when the sun is directly over the
Tropic of Capricorn in the south (
summer solstice). Autumn begins when the sun is again directly over the equator (
autumnal equinox). Winter begins when the sun is directly over the
Tropic of Capricorn in the north or when the sun is directly over the
Tropic of Cancer in the south (
winter solstice).
thumb|left|220px|Tropical sunset over the sea in [[Kota Kinabalu,
Malaysia.]]
Tropical is sometimes used in a general sense for a
tropical climate that is warm to hot and moist year-round, often with the sense of lush vegetation. However, there are places in the tropics that are anything but "tropical" in this sense, with even
alpine tundra and snow-capped peaks, including
Mauna Kea,
Mt. Kilimanjaro, and the
Andes as far south as the northernmost parts of
Chile and
Argentina. 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 and
Australian Outback.
Tropical ecosystems
Coconut Trees amongst the warm, tropical climate in
Brazil.
plants and animals are those species native to the tropics.
Tropical ecosystems may consist of
rainforests, dry deciduous forests, spiny forests,
desert and other habitat types. There are often significant areas of
biodiversity, and species
endemism present particularly in
rainforests and dry deciduous forests. Some examples of important biodiversity and/or high endicism ecosystems are:
Costa Rican and
Nicaraguan rainforests,
Brazilian and
Venezuelan
Amazon Rainforest territories,
Madagascar dry deciduous forests,
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 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 (Central and South America). Together, they are sometimes referred to as the
pantropics. The neotropic region should not be confused with the
ecozone of the same name; in the Old World, this is unambiguous as the paleotropics correspond to the Afrotropical, Indomalayan, and partly the Australasian and Oceanic ecozones.
About 40 percent of the world's human population lives within the
tropical zone (by 2008 statistics), and by 2060 60% of the human population will be in the tropics due to high birth rates and heavy migration to the tropics.
See also
