14.3. Synthesis
There is ample evidence of climate variability at a wide range of time scales
all over Latin America, from intraseasonal to long term. For instance, at decadal
scales, multiple climate records throughout the region consistently exhibit
a shift in the mean during the mid-1970s, which could be a consequence of sudden
changes in the climatology of the Pacific Ocean. These changes have important
socioeconomic and environmental consequences that could be enhanced by global
warming and its associated climate change.
Precipitation changes in Latin America do not follow a consistent trend. In
northwestern Mexico there is a clear tendency for more winter precipitation,
which has resulted in positive trends in river-water level. In north and northwestern
Nicaragua, there is a negative trend in rainfall. In the Amazonian region, the
most important finding is the presence of periods with relatively wetter or
drier conditions that are more relevant than any unidirectional trend. Rainfall
in north-northeast Brazil exhibits a weak positive trend. Precipitation in subtropical
Argentina, Paraguay, and Brazil increased abruptly in the 1956-1990 period
after a dry period from 1921 to 1995. In the Pampas, there was a positive trend
in precipitation over the 1890-1984 period. At higher elevations in northwestern
Argentina, records suggest an increase in precipitation over the past 200 years.
The Southern Oscillation is responsible for a large part of the climate variability
at interannual scales in Latin America. 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, whereas southern Brazil
and northwestern Peru exhibit anomalously wet conditions. Extensive studies
of the Caribbean watersheds of Mexico and other countries show compelling evidence
of more winter and less summer precipitation; in addition, the most severe droughts
in Mexico in recent decades have occurred during El Niño years. In Colombia,
La Niña is associated with heavy precipitation and flooding, whereas
El Niño is associated with negative anomalies in precipitation and river
streamflow. Drought also occurs in southern Brazil during the positive phase
of the Southern Oscillation. If El Niño or La Niña were to increase,
Latin America would be exposed to these conditions more often (see Table
14-6).
| Table 14-6: Variability and impacts
of El Niño and La Niña on several Latin American countries
and subregions. |
 |
| Event |
Climatic/Hydrological
Variable
|
Subregion
or Country
|
Reference(s)
|
Observation
Period
|
|
| El Niñoa |
Severe droughtsb in recent
decades
|
Mexico |
Magaña and Conde, 2000
|
1958-1999c |
| Severe droughts |
Northeast Brazil |
Silva Dias and Marengo, 1999 |
1901-1997 |
| Decrease in precipitation |
Central America (Pacific)
|
Magaña and Conde, 2000 |
1958-1999 |
| Increase in precipitation |
Central America (Atlantic)
|
Magaña and Conde, 2000 |
1958-1999 |
Decrease in precipitation,
soil moisture, river streamflow
|
Colombia |
Poveda and Mesa, 1997
Carvajal et al., 1999
Poveda et al., 2001 |
1958-1995
1957-1997
1958-1998 |
Increase in precipitation and floods
|
Northwest Peru |
Marengo et al., 1998
|
1930-1998 |
Decrease in precipitation
during rainy season
|
Northern Amazonia
and northeast Brazil |
Aceituno, 1988; Richey et al., 1989;
Marengo, 1992; Uvo, 1998
|
1931-1998 |
Negative large anomalies of
rainfall during rainy season
|
Northeast Brazil |
Silva Dias and Marengo, 1999
Hastenrath and Greischar, 1993 |
1930-1998
1912-1989
1849-1984 |
Increase in precipitation
during November-January
time frame
|
Argentina
(Pampas region) |
Nobre and Shukla, 1996 |
1900-1996 |
Intense snowfalls in high
Andes mountains |
Central western Argentina
and central Chile |
Barros et al., 1996; Tanco and Berry,
1996; Vila and Berri, 1996; Vila and Grondona, 1996; Magrin et al.,
1998
|
1900-1995 |
| Increase in runoff |
Chile and central
western Argentina
|
Canziani et al., 1997 |
1906-1994
1909-1998 |
La
Niñad
|
Heavier precipitation and floods |
Colombia
|
Poveda and Mesa, 1997
Carvajal et al., 1999 |
1972-1992
1957-1997 |
| Decrease in precipitation during October-December
time frame
|
Argentina
(Pampas region) |
Barros et al., 1996; Tanco and Berry,
1996; Vila and Berri, 1996; Vila and Grondona, 1996; Magrin et al.,
1998 |
1900-1996
|
Increase in precipitation, higher runoff
|
Northern Amazonia
Northeast Brazil
|
Marengo et al., 1998
Meggers, 1994 |
970-1997
Paleoclimate |
| Severe droughts
|
Southern Brazil
|
Grimm et al., 1996, 2000 |
1956-1992 |
| Negative anomalies of rainfall |
Chile and central western Argentina
|
Compagnucci et al., 2000 |
Paleoclimate |
|
Warming in high mountain regions could lead to disappearance of significant
snow and ice surfaces, which could affect mountain sport and tourist activities.
Because these areas contribute to river streamflow, it also would affect water
availability for irrigation, hydropower generation, and navigation, which represent
important sources of income for some economies. It has been well-established
that glaciers in Latin America have receded in recent decades.
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. Some adverse impacts
on species that can be related to regional climate change have been observed,
such as population declines in frogs and small mammals in Central America. Maintenance
of remaining Amazonian forest is threatened by the combination of human disturbance
and decreased precipitation from evapotranspiration loss, global warming, and
El Niño. Fire in standing forest has increased in frequency and scale
in Amazonia as a result of greater accumulation of deadwood in the forest from
logging activity and from trees killed by past fires, more human settlement
providing opportunities for fire initiation, and dry conditions during ENSO
events. Neotropical seasonally dry forest should be considered severely threatened
in Mesoamerica.
Mortality of trees has been observed to increase under dry conditions that
prevail near newly formed edges in Amazonian forests. Edges, which affect an
increasingly large portion of the forest with the advance of deforestation,
would be especially susceptible to the effects of reduced rainfall. In Mexico,
deciduous tropical forest would be affected in approximately 50% of the area
presently covered by these forests. Heavy rain during the 1997-1998 ENSO
event generated drastic changes in the dry ecosystems of northern Peru's
coastal zone. Increases in biomass burning in Amazonia affected by human activity
and by climate increase wind-borne smoke and dust that supply nutrients to the
Amazon forests. Global warming would expand the area that is 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.
Sea-level rise will eliminate the present habitats of mangroves and create
new tidally inundated areas to which some mangrove species may shift. Coastal
inundation stemming from sea-level rise and riverine and flatland flooding would
affect water availability and agricultural land. These changes can exacerbate
socioeconomic and health problems in critical areas.
On a scale of decades to centuries, it is well-established that changes in
precipitation and catchment runoff may have significant effects on mangrove
forest communities. This also would affect the region's fisheries because
most commercial shellfish and finfish use mangroves as nurseries and for refuge.
Studies in Argentina, Brazil, Chile, Mexico, and Uruguay, based on GCMs and
crop models, project decreased yield for several 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. Predicted
increases in temperature will reduce crops yields in the region by shortening
the crop cycle. Although relationships between the amount of precipitation and
crop yields are well-established, the lack of consistency in the results of
different GCMs means that confidence in the estimated impacts of future precipitation
on crop production is necessarily limited.
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 (e.g., northeastern Brazil).
Evidence is established but incomplete that climate change would reduce silvicultural
yields because water often limits growth during the dry season, which is expected
to become longer and more intense in many parts of Latin America.
The scale of health impacts from climate change in Latin America would depend
primarily on the size, density, location, and wealth of populations. Evidence
has been established but incomplete that exposure to heat or cold waves has
impacts on mortality rates in risk groups in the region.
Increases in temperature would affect human health in polluted cities such
as Mexico City and Santiago. Ample evidence provides high confidence that the
geographical distribution of VBDs in Peru and Cuba (e.g., cholera, meningitis)
would change if temperature and precipitation were to increase, although there
is speculation about what the changes in patterns of diseases would be in different
places. It is well-established that weather disasters (extreme events) tend
to increase death and morbidity rates (injuries, infectious diseases, social
problems, and damage to sanitary infrastructure)—as occurred in Central
America with Hurricane Mitch at the end of 1998, heavy rains in Mexico and Venezuela
at the end of 1999, and in Argentina in 2000. It is well-established that the
ENSO phenomenon causes changes in disease-vector populations and in the incidence
of water-borne diseases in Brazil, Peru, Bolivia, Argentina, and Venezuela.
It has been speculated that weather factors and climate change may affect the
incidence of diseases such as allergies in Mexico. Increased temperature, ultraviolet
radiation, sea-level rise, and changes in pest ecology may threaten food production
in Argentina.
In summary, climate change already has a diverse array of impacts in Latin
America. Projected future changes in climate, together with future changes in
the vulnerability of human and natural systems, could lead to impacts that are
much larger than those experienced to date.
