(continued...)

A series of studies in all of the countries of the Central American isthmus under the Central America Project on Climate Change-with the cooperation of the USCSP-estimated the vulnerability of agricultural resources. These studies were based on scenarios generated through a set of GCMs, including CCC-J1, UKMO-H3, GISS-G1, GFDL-A1, and GFDL-K2. The studies focused on specific crops (e.g., maize, rice, sorghum, beans)-surprisingly enough, however, not on export crops, such as bananas and coffee. A full summary of the results of these studies would be tedious, and they are not highly reliable (as indicated in the Executive Summary of the report, the aforementioned GCMs, in general, are not quite fitted for this type of specific study). Therefore, Box 6-4 presents a case study to provide information about the nature of the results achieved in this first exercise to fulfill the UNFCCC's national reporting requirement.

Regarding the relationship between agriculture and water resources, the studies mentioned above are limited to the known impacts of water deficits on agricultural activities. However, information about some cash crops in countries of the Central American isthmus indicates that, under current climate conditions, the productivity of banana crops is historically affected, particularly in areas already subject to flooding, by environmental conditions associated with tropical storms. This preexisting condition would indicate that, along the Central American-Caribbean watershed, these crops could be additionally stressed if climate change leads to increasing frequency of storms and heavy precipitation (Campos, 1996).

In climatic studies involving projections of GCMs and crop models of wheat, maize, barley, soybeans, potatoes, and grapes in Latin America (Table 6-7), crop yields decreased in the face of climate change-even when direct effects of elevated CO₂ were taken into account-in 9 of 12 studies. Experience available with regard to the development and spread of pests and diseases permits the inference that climate change would trigger many of them and extend their geographical ranges (Austin-Bourke, 1955; Omar, 1980; Pedgley, 1980).

One area that is highly vulnerable to climate change is the Brazilian northeast, which is strongly influenced by the ENSO phenomenon. Years with no rain are frequent; these periods are characterized by the occurrence of famine and large-scale migrations to metropolitan areas (Magalhães and Glantz, 1992; IPCC 1996, WG II, Section 13.7; IPCC 1996, WG III, Section 6.5.9). In the global agricultural model of Rosenzweig et al. (1993), yield impacts of climate change in Brazil are among the most severe for all regions. Under 2xCO₂ scenarios, yields are projected to fall by 17-53%, depending on whether direct effects of CO₂ are considered. Similar reductions also are projected for Uruguay and Mexico (Conde et al., 1996; IPCC 1996, WG II, Section 13.6.6).

Agroindustries that depend on primary production will be vulnerable to climate changes (see Section 6.3.7). Capital-intensive livestock operations, which depend on grassland production, also are likely to be negatively affected (Parry et al., 1988; Baker et al., 1993; Klinedinst et al., 1993). Impacts may be minor, however, for relatively intense livestock production systems (e.g., confined beef, dairy, poultry, swine) (IPCC 1996, WG II, Section 13.5).

Climate change also will affect the distribution and degree of infestation of insects indirectly through climatic effects on hosts, predators, competitors, and insect pathogens. There is some evidence that the risk of crop loss will increase as a result of poleward expansion of insect distribution ranges. Insect species characterized by high reproduction rates generally are favored (Porter et al., 1991). Human alteration of conditions that affect host plant survival-irrigation, for example-also affects phytophagous (leaf-eating) insect populations.

The occurrence of plant fungal and bacterial pests depends on temperature, rainfall, humidity, radiation, and dew. Climatic conditions affect the survival, growth, and spread of pathogens, as well as the resistance of hosts. Friederich (1994) summarizes the observed relationship between climatic conditions and important plant diseases. In Latin America, warm, humid conditions lead to earlier and stronger outbreaks of late potato blight (Phytophthora infestans), as in Chile in the early 1950s (Austin-Bourke, 1955; Löpmeier, 1990; Parry et al., 1990). Warmer temperatures would likely shift the occurrence of these diseases into presently cooler regions (Treharne, 1989).

As a result of these trends, farmers with limited financial resources and farming systems with few adaptive technological opportunities to limit or reverse the impacts of climate change may suffer significant disruption and financial loss from relatively small changes in crop yield and productivity (Parry et al., 1988; Downing, 1992). Conflict is likely to arise between alternative uses of land areas under changing climate conditions-for example, competition for the same land may arise between expanding agriculture and other land uses (e.g., conservation, afforestation, population relocation).

Disparities in agricultural impact between developed and developing countries can be affected by international markets-which can moderate or reinforce local and national exchanges (Reilly et al., 1994; Rosenzweig and Parry, 1994). Countries whose economies rely strongly on agricultural production would face major imbalances between production costs and international prices. According to Rosenzweig and Parry (1994), modeled yield changes in low-latitude countries are primarily negative, even though direct effects of CO₂ on plants, moderate levels of adaptation at the farm level, and production and price responses of the world food system were considered. Economic limitations, social conflicts (e.g., farmers' reluctance to abandon traditional practices), and environmental problems (e.g., salinization resulting from increased irrigation, which is not considered in the models) are likely to severely limit the capacity for adaptation and hinder the expansion of agricultural frontiers. Estimated net economic impacts of climate change on crops are negative for several Latin American countries analyzed by Reilly et al. (1994), even when modest levels of adaptation are considered. The only exception would be Argentina because, as a major exporter of grain, it should benefit from high world prices even if yields fall.

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