South America encompasses an extraordinary range of climates, stretching across nearly every environmental zone found on Earth. This climatic variety is a direct consequence of the continent’s immense scale, extending from the equator deep into the Southern Hemisphere. The continent’s unique geography ensures that it hosts everything from sweltering tropical rainforests to frigid subpolar tundra and hyper-arid deserts.
Primary Drivers of Climate Diversity
The distribution of these diverse climates is governed by three major geographical influences. The sheer latitudinal span of South America means that incoming solar radiation varies drastically, directly influencing baseline temperatures. Solar energy is concentrated near the equator, leading to consistently high temperatures, while the south experiences marked seasonality.
The massive, unbroken north-south wall of the Andes Mountain Range serves as a powerful atmospheric barrier along the western edge. This mountain chain dictates precipitation by creating a significant rain shadow effect, blocking moisture-laden air from the Atlantic and forcing it to drop rain on the eastern slopes. The air descending on the western side is dry, which contributes to the formation of deserts.
Ocean currents also exert profound control over coastal climates. The warm Brazilian Current flows southward along the Atlantic coast, increasing temperature and humidity, supporting the humid subtropical and tropical climates of southeastern Brazil. Conversely, the cold Humboldt (Peru) Current moves northward along the Pacific coast, cooling the overlying air. This prevents moisture from condensing into rain and promotes aridity.
Equatorial and Tropical Zones
The largest climatic area is defined by the Equatorial and Tropical zones, characterized by consistently high temperatures and the dominance of the Tropical Rainforest climate (Af). This zone is centrally located in the vast Amazon Basin, with average temperatures consistently exceeding 18°C throughout the year. Rainfall is heavy and year-round, often exceeding 60 millimeters in every month, meaning there is virtually no seasonal variation.
Moving away from the Amazon, the climate transitions into the Tropical Savanna (Aw) zone, which includes regions like the Cerrado in Brazil and the Llanos in Venezuela and Colombia. This climate type still features high temperatures but experiences a pronounced wet season and a notably dry season. The dry period occurs when the Intertropical Convergence Zone (ITCZ) shifts away, leading to a significant reduction in rainfall.
Arid, Semi-Arid, and Coastal Deserts
The continent hosts some of the driest places on Earth, primarily in the Arid and Semi-Arid zones on the western and southern sides. The hyper-aridity of the Atacama Desert in northern Chile is the result of a unique combination of geographic factors, making it the driest non-polar desert globally. The cold Humboldt Current cools the marine air, leading to a thermal inversion that prevents the formation of rain clouds.
This coastal aridity is intensified by the rain shadow cast by the Andes Mountains, which block moisture from reaching the Pacific coast. Some coastal areas of the Atacama receive moisture from dense marine fog, known as camanchaca, which provides a small but regular source of water for specialized ecosystems. Semi-arid conditions with low and erratic rainfall are also found inland, such as in the Caatinga region of Northeastern Brazil and parts of Argentina.
Temperate, Subpolar, and Highland Climates
In the mid-latitudes of the southeast, the climate shifts to the Temperate zone, specifically the Humid Subtropical climate (Cfa) of the Pampas region of Argentina and Uruguay. This productive agricultural area experiences four distinct seasons, with hot, humid summers and mild winters. Precipitation is distributed relatively evenly throughout the year, supporting the vast grasslands.
Further south in Patagonia and Tierra del Fuego, the climate becomes colder and windier, transitioning into the Subpolar Oceanic or Tundra conditions (ET). This region is characterized by cool to cold temperatures year-round and strong winds, particularly in the southern tip where conditions can be almost polar.
The Alpine or Highland climate (H) exists at high elevations throughout the Andes, regardless of latitude. This climate is defined by rapidly decreasing air temperature and pressure with altitude, leading to low oxygen levels. Significant daily temperature swings occur, where freezing at night can be followed by mild daytime conditions.