There is ample evidence of climate variability at a wide range of time scales all over Latin America, from intraseasonal to long-term. In many subregions of Latin America, this variability in climate normally is associated with phenomena that already produce impacts with important socioeconomic and environmental consequences that could be exacerbated by global warming and its associated weather and climate changes.

Variations in precipitation have a strong effect on runoff and streamflow, which are simultaneously affected by melting of glaciers and snow. Precipitation variations and their sign depend on the geographical subregion under consideration. Temperature in Latin America also varies among subregions. Although these variations might depend on the origin and quality of the source data as well as on the record periods used for studies and analyses, some of these variations could be attributed to a climate change condition (low confidence). [14.1.2.1]

ENSO is responsible for a large part of the climate variability at interannual scales in Latin America (high confidence). The region is vulnerable to El Niño, with impacts varying across the continent. For example, El Niño is associated with dry conditions in northeast Brazil, northern Amazonia, the Peruvian-Bolivian Altiplano, and the Pacific coast of Central America. The most severe droughts in Mexico in recent decades have occurred during El Niño years, whereas southern Brazil and northwestern Peru have exhibited anomalously wet conditions. La Niña is associated with heavy precipitation and flooding in Colombia and drought in southern Brazil. If El Niño or La Niña were to increase, Latin America would be exposed to these conditions more often. [14.1.2]

Some subregions of Latin America frequently experience extreme events, and these extraordinary combinations of hydrological and climatic conditions historically have produced disasters in Latin America. Tropical cyclones and associated heavy rain, flooding, and landslides are very common in Central America and southern Mexico. In northwestern South America and northeastern Brazil, many of the extremes that occur are strongly related to El Niño. [14.1.2]

5.5.1. Water Resources

It has been well established that glaciers in Latin America have receded in the past several decades. Warming in high mountain regions could lead to disappearance of significant snow and ice surface (medium confidence), which could affect mountain sport and tourist activities. Because these areas contribute to river streamflow, this trend also would reduce water availability for irrigation, hydropower generation, and navigation. [14.2.4]

5.5.2. Ecosystems

It is well established that Latin America accounts for one of the Earth's largest concentrations of biodiversity, and the impacts of climate change can be expected to increase the risk of biodiversity loss (high confidence). Observed population declines in frogs and small mammals in Central America can be related to regional climate change. The remaining Amazonian forest is threatened by the combination of human disturbance, increases in fire frequency and scale, and decreased precipitation from evapotranspiration loss, global warming, and El Niño. Neotropical seasonally dry forest should be considered severely threatened in Mesoamerica.

Tree mortality increases under dry conditions that prevail near newly formed edges in Amazonian forests. Edges, which affect an increasingly large portion of the forest because of increased deforestation, would be especially susceptible to the effects of reduced rainfall. In Mexico, nearly 50% of the deciduous tropical forest would be affected. Heavy rain during the 1997-1998 ENSO event generated drastic changes in dry ecosystems of northern Peru's coastal zone. Global warming would expand the area suitable for tropical forests as equilibrium vegetation types. However, the forces driving deforestation make it unlikely that tropical forests will be permitted to occupy these increased areas. Land-use change interacts with climate through positive-feedback processes that accelerate loss of humid tropical forests. [14.2.1]

5.5.3. Sea-Level Rise

Sea-level rise will affect mangrove ecosystems by eliminating their present habitats and creating new tidally inundated areas to which some mangrove species may shift. This also would affect the region's fisheries because most commercial shellfish and finfish use mangroves for nurseries and refuge. Coastal inundation that stems from sea-level rise and riverine and flatland flooding would affect water availability and agricultural land, exacerbating socioeconomic and health problems in these areas. [14.2.3]

5.5.4. Agriculture

Studies in Argentina, Brazil, Chile, Mexico, and Uruguay -- based on GCMs and crop models -- project decreased yields for numerous crops (e.g., maize, wheat, barley, grapes) even when the direct effects of CO₂ fertilization and implementation of moderate adaptation measures at the farm level are considered (high confidence). Predicted increases in temperature will reduce crops yields in the region by shortening the crop cycle. Over the past 40 years, the contribution of agriculture to the GDP of Latin American countries has been on the order of 10%. Agriculture remains a key sector in the regional economy because it employs 30-40% of the economically active population. It also is very important for the food security of the poorest sectors of the population. Subsistence farming could be severely threatened in some parts of Latin America, including northeastern Brazil.

It is established but incomplete that climate change would reduce silvicultural yields because lack of water often limits growth during the dry season, which is expected to become longer and more intense in many parts of Latin America. Table TS-11 summarizes studies undertaken on the region for different crops and management conditions, all under rainfed conditions; most of these results predict negative impacts, particularly for maize. [14.2.2]

Table TS-11: Assessments of climate change impacts on annual crops in Latin America.
Studya	Climate Scenario	Scope	Crop	Yield Impact (%)
Downing, 1992	+3ºC -25% precipitation	Norte Chico, Chile	Wheat	decrease
			Maize	increase
			Potato	increase
			Grapes	decrease
Baethgen, 1994	GISS, GFDL, UKMO	Uruguay	Wheat	-30
			Barley	-40 to -30
de Siqueira et al., 1994	GISS, GFDL, UKMO	Brazil	Wheat	-50 to -15
			Maize	-25 to -2
			Soybeans	-10 to +40
Liverman and O' Brien, 1991	GFDL, GISS	Tlaltizapan, Mexico	Maize	-20
				-24
				-61
Liverman et al., 1994	GISS, GFDL, UKMO	Mexico	Maize	-61 to -6
Sala and Paruelo, 1994	GISS, GFDL, UKMO	Argentina	Maize	-36 to -17
Baethgen and Magrin, 1995	UKMO	Argentina Uruguay (9 sites)	Wheat	-5 to -10
Conde et al., 1997a	CCCM, GFDL	Mexico (7 sites)	Maize	increase-decrease
Magrin et al., 1997a	GISS, UKMO, GFDL, MPI	Argentina (43 sites)	Maize	-16 to +2
			Wheat	-8 to +7
			Sunflower	-8 to +13
			Soybean	-22 to +21
Hofstadter et al., 1997	Incremental	Uruguay	Barley	-10b -8 to +5c
			Maize	-15d -13 to +10c
a See Chapter 14 reference list for complete source information. b For 1ºC increase. c Change of -20 to +20% in precipitation. d For 2ºC increase.

5.5.5. Human Health

The scale of health impacts from climate change in Latin America would depend primarily on the size, density, location, and wealth of populations. Exposure to heat or cold waves has impacts on mortality rates in risk groups in the region (medium confidence).

Increases in temperature would affect human health in polluted cities such as Mexico City and Santiago, Chile. It is well established that ENSO causes changes in disease vector populations and in the incidence of water-borne diseases in Brazil, Peru, Bolivia, Argentina, and Venezuela. Studies in Peru and Cuba indicate that increases in temperature and precipitation would change the geographical distribution of infectious diseases such as cholera and meningitis (high confidence), although there is speculation about what the changes in patterns of diseases would be in different places. It is well established that extreme events tend to increase death and morbidity rates (injuries, infectious diseases, social problems, and damage to sanitary infrastructure), as shown in Central America with Hurricane Mitch in 1998, heavy rains in Mexico and Venezuela in 1999, and in Chile and Argentina in 2000. [14.2.5]

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