Tropic of Capricorn

The Tropic of Capricorn, also known as the Southern Tropic, is one of Earth’s principal lines of latitude and marks the southern boundary of the tropical zone. It represents the latitude at which the Sun appears directly overhead at solar noon during the December solstice, defining a key astronomical and geographical division on the planet. Its position is currently just over 23°26′ south of the Equator and is slowly shifting northwards due to long-term variations in the Earth’s axial tilt.

Astronomical Basis and Nomenclature

The Tropic of Capricorn derives its name from the constellation Capricornus, within which the Sun appeared during the December solstice at the time the latitude was named in antiquity. Although the Sun now appears in the constellation Sagittarius during this solstice due to axial precession, the historical name remains unchanged.
This line of latitude marks the southernmost point at which the Sun can appear at the zenith. During the June solstice, when the Southern Hemisphere experiences winter, the Sun reaches 90 degrees below the horizon at solar midnight along this latitude. Its position is not fixed; instead, it migrates gradually because the Earth’s axial tilt, varying between about 22.1° and 24.5° over a 41,000-year cycle, is currently decreasing. This variation causes a northward drift of approximately 0.47 arcseconds, or around 15 metres per year, and the Tropic is predicted to reach approximately 23°26′ S by 2045.

Geographical and Environmental Context

The Tropic of Capricorn forms the dividing line between the tropical regions to its north and the temperate regions to the south. Despite this neat classification, the environments it passes through vary markedly, from some of the driest on Earth to highly fertile agricultural belts.
Solar radiation fluctuates seasonally along this latitude, resulting in around 10 hours 41 minutes of daylight during the June solstice and 13 hours 35 minutes during the December solstice. Its total length at the current latitude (23°26′ S) is approximately 36,788 kilometres, forming a continuous circumference around the planet.

Africa

Across southern Africa, the Tropic traverses regions of mixed agricultural potential influenced by seasonal rainfall patterns. Much of the area receives sufficient seasonal rain to permit farming, although yields often lag behind those of more temperate agricultural zones such as the Mississippi Basin.
Rivers originating in regions of relief precipitation, such as the Zambezi, have been extensively dammed, enabling effective cultivation in areas enriched by alluvial soils. Pastoral farming is characteristic across the region, and rotational grazing techniques are widely used to maintain soil fertility and prevent erosion and desertification.
Holistic land management approaches, particularly those associated with Allan Savory, have received international attention for their reported success in reversing land degradation. These involve counterintuitive strategies, including increased livestock densities to mimic natural grazing dynamics. The approach has been promoted by the United Nations University’s dissemination platforms and has been discussed in global forums addressing desertification.

Australia

In Australia, the Tropic of Capricorn intersects regions renowned for climatic variability. Eastern areas contain advanced plant communities such as eucalyptus species and native grasses, which are adapted to low transpiration and deep rooting systems. Pastoral farming dominates in areas of seasonal rainfall, while more intensive agriculture is limited by low moisture availability unless supported by irrigation.
The Great Dividing Range plays a crucial role in sustaining agriculture by capturing moisture through relief precipitation, benefitting large parts of New South Wales and Queensland. Beyond this morphological barrier lies a vast rain shadow, stretching thousands of kilometres across interior Australia and producing arid landscapes such as the Channel Country, Kati Thanda–Lake Eyre, Mamungari Conservation Park, and the Gibson Desert.
The Channel Country is known for its ancient flood plains and episodic rivers such as the Georgina River, Diamantina River, and Cooper Creek. These typically evaporate or infiltrate the soil, but in periods of unusual rainfall—such as the event generated by ex-Tropical Cyclone Olga in 2010—they contribute substantial inflow to Lake Eyre. Climate anomalies linked with El Niño phases can significantly reduce rainfall across much of Australia by altering atmospheric circulation and weakening or reversing equatorial trade winds.

South America

In South America, regions close to the Tropic display considerable ecological and agricultural diversity. Although parts of the continent rest on extremely old cratonic soils, the Andes Mountains introduce a major climatic gradient. Areas in Brazil near the Tropic benefit from warm, moist air from the Atlantic Ocean, supporting highly productive agricultural systems, including extensive sugarcane cultivation. Most natural Atlantic Forest vegetation in these regions has been replaced by farmland.
Further south, the Pampas of Argentina represent one of the world’s most significant temperate grassland systems. The region sustains major production of wheat, soybeans, maize, and beef, contributing to Argentina’s status as a global agricultural exporter.
West of the Andes, the influence of the cold Humboldt Current combined with the mountain rain shadow creates extremely arid conditions, culminating in the Atacama Desert, one of the driest places on Earth. The absence of glaciers between Volcán Sajama (approximately 18°30′ S) and Nevado Tres Cruces (near 27° S) illustrates the severity of this aridity. Vegetation in these areas is sparse, although the eastern Andean slopes receive more rainfall and can support rain-fed agriculture.