13.1 Summary of knowledge assessed in the Third Assessment Report

The principal findings in the Third Assessment Report (TAR) (IPCC, 2001) were as follows.

• In most of Latin America, there are no clear long-term tendencies in mean surface temperature. Nevertheless, for some areas in the region, there are some clear warming (Amazonia, north-western South America) and, in a few cases, cooling (Chile) trends.
• Precipitation trends suggest an increase in precipitation for some regions of the mid-latitude Americas, a decrease for some central regions in Latin America, and no clear trends for others. For instance, the positive trends seen in north-eastern Argentina, southern Brazil and north-western Mexico contrast with the negative trends observed in some parts of Central America (e.g., Nicaragua). Records suggest a positive trend for the past 200 years at higher elevations in north-western Argentina. In Amazonia, inter-decadal variability in the hydrological record (in both rainfall and streamflow) is more significant than any observed trend.
• El Niño-Southern Oscillation (ENSO) is the dominant mode of climate variability in Latin America and is the natural phenomenon with the largest socio-economic impacts.
• Glaciers in Latin America have receded dramatically in the past decades, and many of them have disappeared completely. The most affected sub-regions are the Peruvian Andes, southern Chile and Argentina up to latitude 25°S. Deglaciation may have contributed to observed negative trends in streamflows in that region.
• In Latin America many diseases are weather and climate-related through the outbreaks of vectors that develop in warm and humid environments, including malaria and dengue. Climate change could influence the frequency of outbreaks of these diseases by altering the variability associated with the main controlling phenomenon, i.e., El Niño (likely).
• Agriculture in Latin America is a very important economic activity representing about 10% of the gross domestic product (GDP) of the region. Studies in Argentina, Brazil, Chile, Mexico and Uruguay based on General Circulation Models (GCMs) and crop models project decreased yields for numerous crops (e.g., maize, wheat, barley, grapes) even when the direct effects of CO₂-fertilisation and implementation of moderate adaptation measures at the farm level are considered.
• Assessments of the potential impacts of climate change on natural ecosystems indicate that neotropical seasonally dry forest should be considered severely threatened in Mesoamerica. Global warming could expand the area suitable for tropical forests in South America southwards, but current land use makes it unlikely that tropical forests will be permitted to occupy these new areas. On the other hand, large portions of the Amazonian forests could be replaced by tropical savannas due to land-use change and climate change.
• Sea-level rise will affect mangrove ecosystems, damaging the region’s fisheries. Coastal inundation and erosion resulting from sea-level rise in combination with riverine and flatland flooding would affect water quality and availability. Sea-water intrusion would exacerbate socio-economic and health problems in these areas.
• The adaptive capacity of human systems in Latin America is low, particularly to extreme climate events, and vulnerability is high. Adaptation measures have the potential to reduce climate-related losses in agriculture and forestry but less ability to do so for biological diversity.