Environment and Climate
Environment and Climate
The physical environment of Latin America is varied, complex, and frequently spectacular. Extending more than 6,000 miles from north to south, Latin America encompasses environmental conditions from the northern subtropics to the sub-Antarctic. Within this size and diversity there are broad subdivisions.
Mexico continues the surface forms and geology of North America southward to about 20 degrees N, and includes the Pacific and Gulf coastal plains, the upland Mexican plateau at around 8,000 feet, and its peripheral mountain chains. Beyond the Isthmus of Tehuantepec, the circum-Caribbean region consists of the limestone lowland of Yucatán, the rugged east-west mountain ranges of Central America and the Greater Antilles, and the volcanic axes of the Isthmus of Panama and the island arc of the Lesser Antilles.
South America, the largest of the structural elements, itself has three broad subdivisions. Half its area is occupied by the Guiana and Brazilian shields, north and south of the Amazon, and the Patagonian plateau. These geologically ancient and eroded uplands have limited surface relief, but in Brazil substantial scarplike edges form barriers along the Atlantic coast.
On the western margins the Andes extend for more than 5,500 miles as a series of parallel mountain ranges of more than 10,000 feet, rising to 22,800 feet. They divide Pacific from Atlantic drainage, and their rugged topography is a major obstacle to east-west movement. Within the Andes small valleys and upland basins above 10,000 feet have provided important niches for human settlement.
The shields and Andes restrict coastal lowlands, and there are few good harbors. However, between these uplands stretch the broad plains of the Orinoco, Amazon, and Paraná-Paraguay-La Plata river basins. Despite their size, these major rivers have not created arteries of communication into the interior; elsewhere waterfalls, rapids, and shoals limit navigation.
Although three-quarters of the region are within the tropics, there is considerable climatic diversity, in response to the influence of latitude, altitude, and, on the Pacific coast, cold ocean currents. Humid tropical climates have average monthly temperatures above 64 degrees Fahrenheit and annual rainfall of more than 80 inches, with little seasonality; the savanna-type climate has less (30 to 60 inches) and more seasonal rain. The former occurs in Amazonia, the Guianas, the Colombian and Ecuadorian Pacific lowlands, and the circum-Caribbean, and the latter in southern Mexico and the region surrounding the Amazon Basin. Markedly contrasting dry conditions exist in northern Mexico, Patagonia, the Chaco, and the arid coastlands of Peru and north Chile, whereas in northeast Brazil, low, strongly seasonal rainfall may extend into periodic drought. In the mountains, altitude and latitude give a vertical zonation with tropical to cold conditions in Mexico and the central Andes and tundra conditions, with glaciers and permanent snow, in the far south. More restricted but distinctive climates occur in the mediterranean area of central Chile and the subtropical conditions of the pampas, with winter and summer average temperatures of 50 to 82 degrees Fahrenheit and relatively low (20 to 40 inches) but year-round rainfall.
Altitude plays a critically important role in the control of temperature in Latin America, especially in tropical areas, and many different temperature regimes can express themselves over relatively short distances in highland areas. For the most part, highland locations near the equator manifest no real seasonal differences in temperature, although they do show considerable temperature change from day to night. As one moves away from the equator, however, there is an increasingly greater change in temperature from one season to the next. Also, the altitudinal zonations of temperature vary with latitudinal location as well as with their position on the east- or west-facing slope; therefore, altitudinal zonations are not given definite limits. The recognition of the importance of altitudinal zonation goes back at least to the colonial period as the basis for the growing of crops; indigenous peoples too incorporated such insights. It is known that the Incas traditionally moved peoples from one part of their empire to another, but they would always ensure that they stayed at approximately the same altitudinal position.
Many different zonation patterns have been used in the literature, but the traditional folk classification has been the most widely accepted. It divides the highlands into five zones or tierras, each one defined by prevailing temperature regimes, dominant vegetation (although the type of vegetation is also influenced by rainfall regimes), and typical crop complex. The tierra caliente is the region that lies between sea level and about 2,500 to 3,000 feet. Daytime temperatures usually reach 85 to 90 degrees Fahrenheit, and mild temperatures (70 to 75) prevail at night; rarely will temperatures drop below 50, and there is no threat of frost at any time. The tierra templada, considered the most ideal for human occupation and highly desired by the Spaniards, lies between 2,500 and about 6,000 feet. This area typically experiences mild, pleasant days of 75 to 80 degrees, although the mercury will rise to a hot 90 to 95 at higher altitudes during the warmer months. Nighttime temperatures fall to 60 to 70, with a rare frost, especially during the cooler months as one moves north or south from the equator. The tierra fría defines altitudes between 6,000 and 12,000 feet, and occurs throughout the Andes and in some higher elevations in Mexico and Central America. It is known for its mild daytime temperatures (75 to 80) and cool nights (50 to 55), with frost very common in cooler months away from the equator and at higher elevations. The tierra helada lies above 12,000 feet in the Andes, between the daily frost line and the boundary of permanent snow (about 15,000 feet), and is typified by low-growing bunch grasses. The mountain peaks with year-round permanent snow are classified tierra nevada and are above the vegetation zone.
The tierra helada, located above the tree line and below the zone of permanent snow, is a bitterly inhospitable cold desert dominated by highland meadows that provide pasturage for a number of native species (e.g., deer, vicuña, and guanaco) and domesticated animals. These grasslands are referred to as the páramo in the damper highland areas between Costa Rica and northern Peru, but they are replaced by puna in the dry highland Altiplano region between Central Peru and northern Chile. The páramo is typified by a dense tussock grassland with concentrations of woody vegetation in sheltered areas, while the drier puna is dominated by a more xerophytic grassland that includes ichu, a type of poor-quality bunch grass, and tola, a resinous bush that thrives in areas of low temperature and rainfall. In both areas, the use of fire and the cutting of trees have tended to expand the grasslands into lower elevations.
SOILS AND VEGETATION
Poor latosols and podzolic soils, which are strongly weathered and leached, cover almost half the continent. Though they may carry luxuriant vegetation, they have limited nutrients and do not long sustain cultivation. In mountain areas steep slopes and erosion inhibit soil formation. Within such zones tracts of better soils exist, but the most productive soils are the black earths of the pampas and the terra roxa formed on volcanic material in south Brazil.
Vegetation cover reflects the influence of relief, geology, and climate. The three major but internally varied forms are forest, savanna, and desert. Forest cover ranges from the evergreen rain forest of Central America and Amazonia, surrounded by tropical seasonal forest, to the temperate woodlands of southern Chile. The savannas and grasslands occupy almost one-fifth of the area, grading from the woodland-grass scrubland of the Brazilian campos and Venezuelan Llanos to the Pampas grassland. One-quarter of the vegetation is dryland, including the thorn scrub of north Mexico, Patagonia, Chaco, and the Brazilian Sertão and the barren Atacama Desert. In the mountains, altitude modifies cover from tropical forest to puna-páramo grassland and bare rocks.
In the early twenty-first century clear rises in global temperatures, the ongoing deforestation of the Amazon rain forest, and extreme weather conditions made environmental change and protection a major policy concern. Scientists have linked the production of carbon dioxide, mainly by cars and industrial plants, to global warming. The United States contributes the most to atmospheric carbon dioxide pollution whereas Latin America produces approximately 4 percent. Related to this debate has been the deforestation of the Amazon. The vast rain forest, which lies mainly in Brazil, absorbs a great deal of the world's carbon dioxide; in addition, the destruction of trees releases stored carbon dioxide, further contributing to global warming. Consequently, Brazilian and international environmental organizations have opposed the cutting down of the rain forest. Elsewhere, higher temperatures have created noticeable environmental changes: Hurricanes have become more intense and frequent, battering Central America, Mexico and the Caribbean. Ac-cording to the World Bank, global climate change has caused water sources in the Andes to dry up. International and Latin American policymakers are looking at ways of slowing this process and crafting solutions to changes that cannot be halted.
ENVIRONMENT AND PEOPLE
Though the environment can be summarized in these broad terms, to do so would mask much local diversity, in that individual countries have conditions ranging from arid to humid or temperate to tropical. There are negative environments that have been inimical to settlement because of ruggedness, aridity, cold, or soil poverty, or because episodic hazards such as earthquakes, volcanoes, frost, drought, hurricanes, and El Niño put life and economic activity at risk. Conversely, the forest, fertile soils, ecological niches in the mountains, precious and base metals in the sierras and shields, and, more recently, lowland petroleum deposits have attracted people and development.
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John P. Dickenson