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Latin America's mountain chains strongly influence its climate, hydrological cycles, and biodiversity. They are source regions for massive rivers (e.g., the tributaries of the Amazonas and Orinoco basins) and represent major foci of biological diversification and endemism (IPCC 1996, WG II, Section 5.1.4). Mountain areas are exposed to extreme weather and climate events, such as unusually high or low temperatures or precipitation. The Agroclimatological Study of the Andean Zone (Fr�re et al., 1978) provides detailed information on the particular limitations that climate imposes on development in the high South American plateaus and associated mountain ranges in the central Andes (Ecuador, Peru, and Bolivia).
Although the present importance of mountain ecosystems in the national market economies varies from country to country, Andean and extra-Andean mountain ranges have sustained traditional subsistence agriculture for centuries to millennia. Athough the human population density is very low in the northern and southern Andes, the central Andes support the largest percentage rural population in the region.
The cryosphere in the Latin American region is represented by glaciers in the Andes; Patagonia's ice fields (between 47�S and 52�S); and the Darwin ice field in Tierra del Fuego, at about 54�S. Seasonal snowfall on the high Andes is critical for the subsistence of communities in central Chile and large piedmont communities in Argentina, where water supply depends almost entirely on snowmelt.
At present, GCMs do not provide sufficiently accurate regional projections; therefore, scenarios of climate change for Latin American mountain areas are highly uncertain. An added drawback is the scarcity of continuous and reliable meteorological and hydrological records in most areas. If climate changes as projected in Intergovernmental Panel on Climate Change (IPCC) scenarios (Greco et al., 1994), the length of time that snowpacks remain will be reduced, altering the timing and amplitude of runoff from snow/ice and increasing evaporation-hence altering ecosystems at lower elevations and affecting human communities that depend on this runoff. If extreme events increase in frequency or intensity, landslides, flash flooding, and fires would become more likely, and soil instability would increase. Even in subhumid mountain environments, fires in the dry season followed by heavy rainfall events-before substantial vegetation recovery has taken place-usually lead to almost irreversible landscape modification (IPCC 1996, WG II, Section 5.1.3).
Warming in high-mountain regions would lead to the reduction or disappearance of significant snow and ice surfaces (IPCC 1996, WG II, Sections 7.4.1 and 7.4.2). Furthermore, changes in atmospheric circulation stemming from global warming may modify snowfall rates, with a direct effect on the seasonal renewal of water supply and the variability of runoff and underground water supplies in piedmont areas (Del Carril et al., 1996). Glaciers are melting at accelerated rates in the Venezuelan and Peruvian Andes (Schubert, 1992; Hastenrath and Ames, 1995), as well as at the southern extreme of the subcontinent (Aniya et al., 1992; Kadota et al., 1992; Malagnino and Strelin, 1992). Nevertheless, larger glaciers, such as those in the Patagonian Andes, should continue to exist into the 22nd century. More water would be released from regions with extensive glaciers; as a result, some arid regions in their vicinity would benefit from additional runoff. Based on seasonal patterns and extreme events in these regions, however, this runoff could trigger major erosion, flooding, and sedimentation problems (IPCC 1996, WG II, Section 7.2.2). Melting of Andean glaciers and ice fields in southern Patagonia and Tierra del Fuego would increase runoff, as well as the water levels of neighboring rivers and lakes on both sides of the Andes.
Expected impacts of climate change on the biological diversity of mountain ecosystems would include loss of the coolest climatic zones toward the peaks of the mountains and shifting of remaining vegetation belts upslope, resulting in a net decrease in biodiversity. Mountaintops may become more vulnerable to genetic and environmental pressure (Bortenschlager, 1993; IPCC 1996, WG II, Section 5.2.2).
Viable areas for crop production in mountainous regions would likely change as a result of climate change. Elevational shifts in vegetation and altered hydrological patterns may have major implications for the use and conservation of multiple vegetation belts by traditional Andean peoples. These shifts may lead to competition between alternative land uses (e.g., conservation of endangered species versus expansion of subsistence agriculture) toward the mountaintops. Given the wide range of microclimates in Latin America's mountain areas that have been exploited through the cultivation of diverse crops, direct negative effects of climate change on crop yields may not be extremely serious. However, continued adaptation to varied climates may be possible only if the remarkable diversity of local genotypes is conserved. Development planners and decision makers should be fully aware that the protection of the wide variety of wild and domesticated genotypes of major crops in the Andes also will be crucial for the production of new crop varieties in the face of changing climatic conditions in other areas of the world. In 1960, for example, the discovery of two varieties of tomato in Peru provided the industry with economic benefits estimated at US$5 million per year (LAC CDE, 1992). Decision makers also should be aware that, unless appropriate adaptation measures are taken, climate change could completely disrupt lifestyles in mountain villages by altering already marginal food production and the availability of water resources.
Shifts in crop and rangeland elevation belts may be dramatic in rural, densely populated areas of the central Andes; deep socioeconomic changes have been brought about by past climatic pulses (Cardich, 1974; Fr�re et al., 1978). Studies of the effects of climate change in Ecuador's central Sierra (Parry, 1978; Bravo et al., 1988) have shown that crop growth and yields are controlled by complex interactions among different climatic factors and that specific methods of cultivation may permit crop survival in sites where microclimates otherwise would be unsuitable. Such specific details cannot be included in GCM-based impact assessments-which have suggested positive impacts, such as decreasing frost risks in the Mexican highlands (Liverman and O'Brien, 1991), and negative impacts, such as decreases in the productivity of upland agriculture (Parry et al., 1990).
In many mountain regions, tourist resorts and large urban areas close to the mountains have spread into high-risk areas; these areas will be increasingly endangered by slope instability and flood risk, particularly as a consequence of extreme events aggravated by climate change. Such situations already have been observed in Andean cities (Bogota, La Paz, Mendoza, Quito); cities on the Serra do Mar mountain range (Rio de Janeiro, Sao Paulo, Santos) and their outskirts; and Guatemala City, in Central America.
Runoff changes resulting from snow/ice melting and from changes in winter snowfalls on high-altitude mountains would affect important sectors and activities (freshwater supply, agriculture, industry, and power generation) in the Andes piedmont areas (e.g., Cuyo region in Argentina, Elqui Valley in Chile). In view of the economic importance of these activities, adaptation measures are likely to be necessary (Fuenzalida et al., 1993; Del Carril et al., 1996; IPCC 1996, WG II, Section 5.2.4).
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