Summary of expected key future impacts and vulnerabilities

13.4.1 Natural ecosystems

Tropical plant species may be sensitive to small variations of climate, since biological systems respond slowly to relatively rapid changes of climate. This fact might lead to a decrease of species diversity. Based on Hadley Centre Atmosphere-Ocean General Circulation Model (AOGCM) projections for A2 emissions scenarios, there is the potential for extinction of 24%

of 138 tree species of the central Brazil savannas (Cerrados) by 2050 for a projected increase of 2°C in surface temperature (Siqueira and Peterson, 2003; Thomas et al., 2004). By the end of the century, 43% of 69 tree plant species studied could become extinct in Amazonia (Miles et al., 2004). In terms of species and biome redistributions, larger impacts would occur over north-east Amazonia than over western Amazonia. Several AOGCM scenarios indicate a tendency towards 'savannisation' of eastern Amazonia (Nobre et al., 2005) and the tropical forests of central and south Mexico (Peterson et al., 2002; Arriaga and Gómez, 2004). In north-east Brazil the semi-arid vegetation would be replaced by the vegetation of arid regions (Nobre et al., 2005), as in most of central and northern Mexico (Villers and Trejo, 2004).

Up to 40% of the Amazonian forests could react drastically to even a slight reduction in precipitation; this means that the tropical vegetation, hydrology and climate system in South America could change very rapidly to another steady state, not necessarily producing gradual changes between the current and the future situation (Rowell and Moore, 2000). It is more probable that forests will be replaced by ecosystems that have more resistance to multiple stresses caused by temperature increase, droughts and fires, such as tropical savannas.

The study of climate-induced changes in key ecosystem processes (Scholze et al., 2005) considers the distribution of outcomes within three sets of model runs grouped according to the amount of global warming they simulate: <2°C, 2-3°C and >3°C. A high risk of forest loss is shown for Central America and Amazonia, more frequent wildfire in Amazonia, more runoff in north-western South America, and less runoff in Central America. More frequent wildfires are likely (an increase in frequency of 60% for a temperature increase of 3°C) in much of South America. Extant forests are destroyed with lower probability in Central America and Amazonia. The risks of forest losses in some parts of Amazonia exceed 40% for temperature increases of more than 3°C (see Figure 13.3).

The tropical cloud forests in mountainous regions will be threatened if temperatures increase by 1°C to 2°C during the next 50 years due to changes in the altitude of the cloud-base during the dry season, which would be rising by 2 m/yr. In places with low elevation and isolated mountains, some plants will become locally extinct because the elevation range would not permit natural adaptation to temperature increase (FAO, 2002). The change in temperature and cloud-base in these forests could have substantial effects on the diversity and composition of species. For example, in the cloud forest of Monteverde Costa Rica, these changes are already happening. Declines in the frequency of mist days have been strongly associated with a decrease in population of amphibians (20 of 50 species) and probably also bird and reptile populations (Pounds et al., 1999).

Modelling studies show that the ranges occupied by many species will become unsuitable for them as the climate changes (IUCN, 2004). Using modelling projections of species distributions for future climate scenarios, Thomas et al. (2004) show, for the year 2050 and for a mid-range climate change scenario, that species extinction in Mexico could sharply increase: mammals 8% or 26% loss of species (with or without dispersal), birds 5% or 8% loss of species (with or without dispersal), and butterflies 7% or 19% loss of species (with or without dispersal).

13.4.2 Agriculture

Several studies using crop-simulation models and future climate scenarios were carried out in Latin America for commercial annual crops (see Table 13.5). According to a global assessment (Parry et al., 2004), if CO2 effects are not considered, grain yield reductions could reach up to 30% by 2080 under the warmer scenario (HadCM3 SRES A1FI), and the number of additional people at risk of hunger under the A2 scenario is likely to reach 5, 26 and 85 million in 2020, 2050 and 2080, respectively (Warren et al., 2006). However, if direct CO2 effects are considered, yield changes could range between reductions of 30% in Mexico and increases of 5% in Argentina (Parry et al., 2004), and the additional number of people at risk of hunger under SRES A2 would increase by 1 million in 2020, remain unchanged in 2050 and decrease by 4 million in 2080.

More specific studies considering individual crops and countries are also presented in Table 13.5. The great uncertainty in yield projections could be attributed to differences in the GCM or incremental scenario used, the time-slice and SRES scenario considered, the inclusion or not of CO2 effects, and the site considered. Other uncertainties in yield impacts are derived from model inaccuracies and unmodelled processes. Despite great variability in yield projections, some behaviour seems to be consistent all over the region, such as the projected reduction in rice yields after the year 2010 and the increase in soybean yields when CO2 effects are considered. Larger crop yield reductions could be expected in the future if the variance of temperatures were doubled (see Table 13.5). For smallholders a mean reduction of 10% in maize yields could be expected by 2055, although in Colombia yields remain essentially unchanged, while in the Venezuelan Piedmont yields are predicted to decline to almost zero (Jones and Thornton, 2003). Furthermore, an increase in heat stress and more dry soils may reduce yields to one-third in tropical and sub-tropical areas where crops are already near their maximum heat tolerance. The productivity of both prairies/meadows and pastures will be affected, with loss of carbon stock in organic soils and also a loss of organic matter (FAO, 2001b). Other important issues are the expected reductions in land suitable for growing coffee in Brazil, and in coffee production in Mexico (see Table 13.5).

In temperate areas, such as the Argentinean and Uruguayan Pampas, pasture productivity could increase by between 1% and 9% according to HadCM3 projections under SRES A2 for 2020 (Gimenez, 2006). As far as beef cattle production is concerned, in Bolivia future climatic scenarios would have a slight impact on animal weight if CO2 effects are not considered, while doubling CO2 and increases of 4°C in temperature are very likely to result in decreases in weight that could be as much as 20%, depending on animal genotype and region (NC-Bolivia, 2000).

Furthermore, the combined effects of climate change and land-use change on food production and food security are related to a larger degradation of lands and a change in erosion patterns (FAO, 2001b). According to the World Bank (2002a, c), some developing countries are losing 4-8% of their GDP due to productive and capital losses related to environmental degradation. In drier areas of Latin America, such as central and northern Chile, the Peruvian coast, north-east Brazil, dry Gran Chaco and Cuyo, central, western and north-west Argentina and significant parts of Mesoamerica (Oropeza, 2004), climate change is likely to lead to salinisation and desertification of agricultural lands. By 2050, desertification and salinisation will affect 50% of agricultural lands in Latin America and the Caribbean zone (FAO, 2004a).

In relation to pests and diseases, the incidence of the coffee leafminer (Perileucoptera coffeella) and the nematode Meloidogyne incognita are likely to increase in future in Brazil's production area. The number of coffee leafminer cycles could increase by 4%, 32% and 61% in 2020, 2050 and 2080, respectively, under SRES A2 scenarios (Ghini et al., 2007). According to Fernandes et al. (2004), the risk of Fusarium head blight incidence in wheat crops is very likely to increase under climate change in south Brazil and Uruguay. The demand for water for irrigation is projected to rise in a warmer climate, bringing increased competition between agricultural and domestic use in addition to industrial uses. Falling watertables and the resulting increase in the energy used for pumping will make the practice of agriculture more expensive (Maza et al., 2001). In the state of Ceara (Brazil), large-scale reductions in the availability of stored surface water could lead to an increasing imbalance between water demand and water supply after 2025 (ECHAM scenario; Krol and van Oel, 2004).

13.4.3 Water resources

Almost 13.9% of the Latin American population (71.5 million people) have no access to a safe water supply; 63% of these (45 million people) live in rural areas (IDB, 2004). Many rural communities rely on limited freshwater resources (surface or underground) and many others on rainwater, using water-cropping methods which are very vulnerable to drought (IDB, 2004). People living in water-stressed watersheds (less than 1,000 m3/capita per year) in the absence of climate change were estimated to number 22.2 million in 1995 (Arnell, 2004). The number of people experiencing increased water stress under the SRES scenarios is estimated to range from 12 to 81 million in the 2020s, and from 79 to 178 million in the 2050s (Arnell, 2004). These estimates do not take into account the number of people moving out of water-stressed areas (unlike Table 13.6). The current vulnerabilities observed in many regions of Latin American countries will be increased by the joint negative effects of growing demands for water supplies for domestic use and irrigation due to an increasing population, and the expected drier conditions in many basins. Therefore, taking into account the number of people experiencing decreased water stress, there will still be a net increase in the number of people becoming water-stressed (see Table 13.6).

In some zones of Latin America where severe water stresses could be expected (eastern Central America, in the plains, Motagua valley and Pacific slopes of Guatemala, eastern and western regions of El Salvador, the central valley and Pacific region of Costa Rica, in the northern, central and western intermontane regions of Honduras and in the peninsula of Azuero in Panama), water supply and hydroelectric generation would be seriously affected (Ramirez and Brenes, 2001; ECLAC, 2002a).

Table 13.5. Future impacts on the agricultural sector.

Yield impacts (%)

Study

Climate scenario

Wheat

Maize

Soybean

Rice

(NC-Guyana, 2002)

CGCM1 2020-2040 (2xCO2) CGCM1 2080-2100 (3xCO2)

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