Latin America includes all continental countries of the Americas from Mexico to Chile and Argentina, as well as adjacent seas. The region is highly heterogeneous in terms of climate, ecosystems, human population distribution, and cultural traditions. Most Latin American production activities are based on the region's extensive natural ecosystems. Land use is a major force driving ecosystem change at present; it interacts with climate in complex ways. This complexity makes the task of identifying common patterns of vulnerability to climate change very difficult. Major sectors in which the impacts of climate change could be important are natural ecosystems (e.g., forests, rangelands, wetlands), water resources, coastal zones, agriculture, and human health. The relative importance attributed to each of these projected impacts varies among countries.
Changes in climate over the past century have included a rise in the mean surface temperature, particularly at middle and high latitudes, and changes in precipitation rates and intensities in various countries of the region (e.g., southern Brazil, Paraguay, Argentina). Climate change could modify present conditions, with beneficial or adverse impacts-as presently occurs as a result of the El Ni�o-Southern Oscillation (ENSO) phenomenon. Natural climate variability at the time scale of seasons to several years has produced significant effects on Latin American countries, suggesting that climate change projections become an important element for national and regional planning. However, climate change should be considered not in isolation but in close interaction with other important factors for development, such as land-use practices and land-use change, population growth, economic situations, and community behavior.
Latin America's geographical location and geomorphology contribute to its large variety of climates, ranging from hyper-arid desert climates to humid tropical forest climates. The regional climate distribution is defined by interactions among the predominant atmospheric circulation patterns and the region's topographical features, radiation budgets, and heat and water balances-which, in turn, depend on the vast range of soil/vegetation types of the region. The extensive central portion of Latin America is characterized largely by humid, tropical conditions; important areas (e.g., in Brazil) are subject to drought, floods, and freezes. Atmospheric circulation and ocean currents are causal factors of extensive deserts in northern Mexico, Peru, Bolivia, Chile, and Argentina.
The relationship between the ENSO phenomenon and changes in precipitation and temperature has been well documented for countries of the Central American isthmus and South America. ENSO events associated with massive fluctuations in the marine ecosystems off the coasts of Ecuador, Peru, and northern Chile (which are among the richest fisheries in the world) would have adverse socioeconomic consequences on fishing and fishmeal production. Experimental El Ni�o forecasts have been applied, with remarkable success, in Peru and Brazil to reduce economic disruptions in agriculture. Climate variability also determines important changes in the distribution and intensity of rainfall and snow. This variability represents an additional stress on already limited freshwater availability in Chile and western Argentina at latitudes between 25�S and 37�S.
The surface area of Latin America is occupied by natural ecosystems whose genetic resources are among the richest in the world. The Amazon rainforest contains the largest number of animal and plant species in Latin America. Temperate and arid zones in this region-which, until recently, have received less attention-also contain important genetic resources, in terms of wild and domesticated genotypes.
The Latin American contribution to global emissions of greenhouse gases is low at present (approximately 4%). However, potential future impacts of climate and land-use changes could be large and costly for this region. In addition, the release of carbon to the atmosphere as a consequence of massive and continued deforestation in Latin America would have the potential to alter the global carbon balance. On the other hand, some studies suggest that technologically simple adaptation options could improve the capacity for carbon sequestration, as well as economic productivity, in some ecosystems.
Latin American forests-which occupy approximately 22% of the region and represent about 27% of global forest coverage-have a strong influence on local and regional climate, play a significant role in the global carbon budget, contain an important share of all plant and animal species of the region, and are economically very important for national and international markets. Vulnerability studies indicate that forest ecosystems in many countries (e.g., Mexico, countries of the Central American isthmus, Venezuela, Brazil, Bolivia) could be affected by projected climatic changes. Deforestation in the Amazon rainforest is likely to have a negative impact on the recycling of precipitation through evapotranspiration. Rainfall would be markedly reduced, leading to important runoff losses in areas within and beyond this basin.
Rangelands cover about one-third of the land area of Latin America. Rangeland productivity and species composition are directly related to the highly variable amount and seasonal distribution of precipitation; they are only secondarily affected by other climate variables (with the exception of high-temperature persistence in wildfire-prone areas). Temperate grasslands are vulnerable to drought; therefore, livestock production would drop drastically if precipitation decreased substantially or if higher temperatures led to increased evapotranspiration rates. An increased frequency of extreme events is likely to have larger impacts than changes in mean temperature or precipitation. The preservation of large-scale range management units and protected areas may assist migration and recolonization by native species in response to changing environmental conditions.
Mountain ranges and plateaus play an important role in determining Latin America's climate, hydrological cycle, and biodiversity. They are source regions of massive rivers (e.g., the tributary rivers of the Amazonas and Orinoco basins) and represent important foci of biological diversification and endemism-and they are highly susceptible to extreme events. The cryosphere in Latin America is represented by glaciers in the high Andes and three major ice fields in southern South America. Warming in high mountain regions could lead to the disappearance of significant snow and ice surfaces. In addition, changes in atmospheric circulation resulting from the ENSO phenomenon and climate change could modify snowfall rates-with a direct effect on the seasonal renewal of water supply-and surface and underground runoff in piedmont areas. This could affect mountain sports and tourist activities, which represent an important source of income in some economies. Glaciers are melting at an accelerated rate in the Venezuelan and Peruvian Andes; however, the largest glaciers in the Patagonian Andes would continue to exist into the 22nd century.
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