The Latin America region is remarkably heterogeneous in terms of climate, ecosystems, human population distribution, and cultural traditions. Land-use changes have become a major force driving ecosystem changes. Complex climatic patterns, which result in part from interactions of atmospheric flow with topography, intermingled with land-use and land-cover change, make it difficult to identify common patterns of vulnerability to climate change in the region. Water resources, ecosystems, agriculture and plantation forestry, sea-level rise, and human health may be considered the most important among the various sectors that may be impacted by climate change.

Climate, Extreme Events, and Water Resources

In most of Latin America, there are no clear long-term tendencies in mean surface temperature. Some changes in regional atmospheric circulation have been detected. For instance, the south Atlantic anticyclone has intensified, and the subtropical jet stream in South America has shifted south. These phenomena may be a sign of changes associated with climate change as they already are impacted by the El Niño-Southern Oscillation (ENSO) phenomena and extreme events.

The cryosphere in Latin America, which is composed of glaciers in the high Andes and three major ice areas in southern South America, may be severely affected by global warming. It has been well established that glaciers in Latin America, particularly along the tropical Andes, have receded in recent decades. Glaciers contribute to streamflow in rivers of semi-arid and arid areas of South America. Streamflows in Andean rivers—for example, in northwest Peru—exhibit tendencies that may be related to glacial extent changes before and after the mid-1970s. However, there also is evidence that rainfall and river flows in other regions of Latin America correspond only to interdecadal variability in the hydrological cycle. For instance, rainfall and streamflow in Amazonia and northeast Brazil exhibit interdecadal variability linked to Pacific and Atlantic Ocean influences. Warming in high mountains also could affect mountain sports and tourist activities, which represent an important source of income in the economies of some countries in the region.

At a subregional level, precipitation trends in Latin America vary. Precipitation trends depend on the location and the length of the time series under study. For instance, negative trends in some parts of Central America (e.g., Nicaragua) contrast with positive trends in northeastern Argentina, southern Brazil, and northwestern Mexico. Other regions, such as central-western Argentina, do not show well-defined trends. This suggests, for instance, an increase in precipitation in some regions of the mid-latitude Americas.

The Amazon River—by far the world's largest river in terms of streamflow—plays an important role in the water cycle and water balance of much of South America. Several model studies and field experiments show that about 50% of the rainfall in the region originates as water recycled in the forest. In the Amazon region, even small changes in evapotranspiration affect water vapor fluxes. Therefore, deforestation is likely to reduce precipitation because of a decrease in evapotranspiration, leading to important runoff losses in areas within and beyond this basin. Any reductions in rainfall would affect not only Amazonia but also Brazil's central-south region, where most of the country's agriculture and silviculture are located. However, with the current rate of deforestation of no more than 10% in Amazonia as a whole, discharge observations across the basin do not exhibit, to date, any significant trends.

Although it is expected that tropical storms (e.g., tropical cyclones) will increase their peak intensity under global warming (see Table 3-10), only some hints of such intensification in the tropical cyclones affecting the Americas have been detected. Some studies based on model experiments suggest that under climate change the hydrological cycle will be more intense, with changes in the distribution of extreme heavy rainfall, wet spells, and dry spells. Frequent severe droughts in Mexico during the past decade coincide with some of these model findings. Even though it is uncertain how global warming may affect the frequency and intensity of some extreme events, the infrequent overlapping of hydrological and weather/climate events historically have given rise to disasters, whose frequency may be enhanced by such warming.

El Niño

It also has been suggested that under climate change, more El Niño-like mean conditions will be experienced. El Niño differentially influences precipitation and temperature in different parts of the region; for example, it is related to dry conditions in northern northeast Brazil, northern Amazonia, and the Peruvian-Bolivian Altiplano. Southern Brazil and northwest Peru exhibit anomalously wet conditions during these periods. In Mexico and the Caribbean coast of Central America, there is compelling evidence of more winter precipitation and less summer precipitation during El Niño. Some of the most severe droughts in Mexico in recent decades have occurred during El Niño years. During the 1997-1998 El Niño event, droughts occurred in Amazonia, Mexico, and Central America, favoring forest fires. Under climate change conditions, the number of forest fires may increase.

Natural Ecosystems

Latin America contains a large percentage of the world's biodiversity, and climate change could accelerate losses in biodiversity that already are occurring. Some adverse impacts on species that can be related to regional changes in climate have been observed. Studies show that climatic changes already are affecting frogs and small mammals in Central America. The tropical forests play an important role in the hydrological cycle of much of South America. Several model studies and field experiments show that a large part of the rainfall in the region originates as water recycled in the forest. Large-scale deforestation is likely to result in increased surface temperatures, decreased evapotranspiration, and reduced precipitation. Forest fragmentation and degradation has led to increased vulnerability of forests to fire. Global warming and regional climate change resulting from land-cover change may be acting synergistically to exacerbate stress over the region's tropical ecosystems.

Mountain ranges and plateaus play an important role in determining not only the Latin America climate and its hydrological cycle but also its large biodiversity. Mountains constitute source regions of major rivers such as the Amazon, the Parana, and the Orinoco. These river basins represent important habitats of biological diversity and endemism and are highly vulnerable to extreme climate conditions.

On decadal to centennial time scales, changes in precipitation and runoff may have significant impacts on mangrove forest communities. Sea-level rise would eliminate mangrove habitat at an approximate rate of 1% yr^-1. The rate is much faster in the Caribbean mainland (approximately 1.7% yr^-1). This problem is causing a decline in some of the region's fisheries at a similar rate because most commercial shellfish use mangroves as nurseries or refuges. Coastal inundation stemming from sea-level rise or flatland flooding resulting from climate change therefore may seriously affect mangrove ecology and associated human economy.

Agriculture

Agricultural lands (excluding pastures) represent approximately 19% of the total area of Latin America. For the past 40 years, the contribution of agriculture to the gross domestic product (GDP) of Latin American countries has been on the order of 10%. Therefore, this economic sector remains a key element of the regional economy. An important aspect of this sector is that a large percentage (30-40%) of the economically active population works in this sector. Agriculture also is an important element for the food security of the poorest sectors of the population. Under climate change conditions, subsistence farming could be severely threatened in some parts of Latin America, such as northeastern Brazil.

Studies in Argentina, Brazil, Chile, Mexico, and Uruguay based on general circulation models (GCMs) and crop models project decreased yields in several crops (e.g., maize, wheat, barley, grapes), even when the direct effect of carbon dioxide (CO₂) fertilization and the implementation of moderate adaptation measures at the farm level are considered. It is likely that increases in temperature will reduce crop yields in the region by shortening the crop cycle. However, the lack of consistency in the various GCM precipitation scenarios makes it difficult to have a precise scenario for crop production under climate change, even when the relationships between precipitation and crop yields are well known. Increased temperature, ultraviolet radiation, sea-level rise, and changes in pest ecology may threaten food production as well (e.g., in Argentina). Climate change may reduce silvicultural yields as a result of changes in water availability during the dry season.

Human Health

The magnitude of the impacts of climate change on health in Latin America primarily depends on the size, density, location, and wealth of the population. It has been established that exposure to heat or cold waves has an influence on mortality rates in risk groups in the region. The projected increase in temperature in polluted cities, such as Mexico City or Santiago, may have an influence on human health. There is evidence that the geographical distributions of vector-borne diseases (e.g., malaria, dengue) in Brazil, Colombia, Argentina, and Honduras and infectious diseases (e.g., cholera, meningitis) in Peru and Cuba change when temperature and precipitation increase. The exact distribution of these diseases, however, is not clear.

It is likely that extreme weather events will increase death and morbidity rates (injuries, infectious diseases, social problems, and damage to sanitary infrastructure), as during the heavy rains in Mexico in 1999 or in Venezuela in 1999. On longer time scales, El Niño and La Niña cause changes in disease vector populations and the incidence of water-borne diseases in Brazil, Peru, Bolivia, Argentina, and Venezuela. Extreme climate events appear to affect the incidence of allergies in Mexico. Some economic and health problems could be exacerbated in critical areas, fostering migrations from rural and small urban settlements into major cities and giving rise to additional stress at the national level and, at times, adversely affecting international relations between neighboring countries. Therefore, under climate change conditions the risks for human health in Latin America may increase.

Adaptation Potential and Vulnerability

The economy of Latin American countries can be severely affected by extremes of natural climate variability. There were more than 700 natural disasters in the region between 1980 and 1998. For instance, Hurricane Mitch in 1998 resulted in economic losses of approximately 40 and 70% of the gross national product (GNP) in Nicaragua and Honduras, respectively. Poverty and unequal distribution of wealth may increase as a result of the negative effects of climate change.

Trade agreements are becoming increasingly important for Latin American economies. In principle, they have been designed mainly to speed up socioeconomic development. However, various elements that relate to environmental issues gradually are being introduced into these agreements, including provisions related to climate change. Environmental issues are beginning to be reflected in the environmental legislation in the region. For instance, environmental impact assessments are now required in most project developments.

Although climate change may bring benefits for certain regions of Latin America, increasing environmental deterioration, combined with changes in water availability and agricultural lands, may reduce these benefits to a negligible level. The adaptive capacity of socioeconomic systems in Latin America is very low, particularly with respect to extreme climate events, and vulnerability is high.

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