13.2.4 Past and current trends

13.2.4.1 Climate trends

During the 20th century, significant increases in precipitation were observed in southern Brazil, Paraguay, Uruguay, north-east Argentina and north-west Peru and Ecuador. Conversely, a declining trend in precipitation was observed in southern Chile, south-west Argentina and southern Peru (Figure 13.1, Table 13.2). In addition, increases in the rate of sea-level rise have reached 2-3 mm/yr during the last 10-20 years in south-eastern South America (Table 13.2).

Figure 13.1. Trends in rainfall in (a) South America (1960-2000). An increase is shown by a plus sign, a decrease by a circle. Bold values indicate significance at P ² 0.05. Haylock et al. (2006); reprinted with permission from the American Meteorological Society. (b) Central America and northern South America (1961-2003). Large red triangles indicate positive significant trends, small red triangles indicate positive non-significant trends, large blue triangles indicate negative significant trends, and small blue triangles indicate negative non-significant trends. Aguilar et al. (2005); reprinted with permission from the American Geophysical Union.

A number of regional studies have been completed for southern South America (Vincent et al., 2005; Alexander et al., 2006; Haylock et al., 2006; Marengo and Camargo, 2007), Central America and northern South America (Poveda et al., 2001a; Aguilar et al., 2005; Alexander et al., 2006). They all show patterns of changes in extremes consistent with a general warming, especially positive trends for warm nights and negative trends for the occurrence of cold nights. There is also a positive tendency for intense rainfall events and consecutive dry days. A study by Groisman et al. (2005) identified positive linear trends in the frequency of very heavy rains over north-east Brazil and central Mexico. However, the lack of long-term records of daily temperature and rainfall in most of tropical South America does not allow for any conclusive evidence of trends in extreme events in regions such as Amazonia. Chapter 3, Section 3.8 of the Working Group I Fourth Assessment Report (Trenberth et al., 2007) discusses observational aspects of variability of extreme events and tropical cyclones. Chapter 11, Section 11.6 of the Working Group I Fourth Assessment Report (Christensen et al., 2007) acknowledges that little research is available on extremes of temperature and precipitation for this region.

These changes in climate are already affecting several sectors. Some reported impacts associated with heavy precipitation are: 10% increase in flood frequency due to increased annual discharge in the Amazon River at Obidos (Callède et al., 2004); increases of up to 50% in streamflow in the rivers Uruguay, Paraná and Paraguay (Bidegain et al., 2005; Camilloni, 2005b); floods in the Mamore basin in Bolivian Amazonia (Ronchail et al., 2005); and increases in morbidity and mortality due to flooding, landslides and storms in Bolivia (NC-Bolivia, 2000). In addition, positive impacts were reported for the Argentinean Pampas region, where increases in precipitation led to increases in crop yields close to 38% in soybean, 18% in maize, 13% in wheat and 12% in sunflower (Magrin et al., 2005). In the same way, pasture productivity increased by 7% in Argentina and Uruguay (Gimenez, 2006).

The glacier-retreat trend reported in the TAR has intensified, reaching critical conditions in Bolivia, Peru, Colombia and Ecuador (Table 13.3). Recent studies indicate that most of the South American glaciers from Colombia to Chile and Argentina (up to 25°S) are drastically reducing their volume at an accelerated rate (Mark and Seltzer, 2003; Leiva, 2006). Changes in temperature and humidity are the primary cause of the observed glacier retreat during the second half of the 20th century in the tropical Andes (Vuille et al., 2003). During the next 15 years, inter-tropical glaciers are very likely to disappear, affecting water availability and hydropower generation (Ramírez et al., 2001).

13.2.4.2 Environmental trends

Deforestation and changes in land use

In 1990, the total forest area in Latin America was 1,011 Mha, which has reduced by 46.7 Mha in the 10 years from 1990 to 2000 (UNEP, 2003a) (Figure 13.2). In Amazonia, the total area of forest lost rose by 17.2 Mha from 41.5 Mha in 1990 to 58.7 Mha in 2000 (Kaimowitz et al., 2004). The expansion of the agricultural frontier and livestock, selective logging, financing of large-scale projects such as the construction of dams for energy generation, illegal crops, the construction of roads and increased links to commercial markets have been the main causes of deforestation (FAO, 2001a; Laurance et al., 2001; Geist and Lambin, 2002; Asner et al., 2005; FAO, 2005; Colombia Trade News, 2006).

Figure 13.2. Total deforestation in Latin America (Mha) between 1990 and 2000. Number indicates deforestation rate (%/yr) for each country. Based on FAO (2001a).

Natural land cover has continued to decline at very high rates. In particular, rates of deforestation of tropical forests have increased during the last five years. Annual deforestation in Brazilian Amazonia increased by 32% between 1996 and 2000 (1.68 Mha) and 2001 and 2005 (2.23 Mha). However, the annual rate of deforestation decreased from 2.61 Mha in 2004 to 1.89 Mha in 2005 (INPE-MMA, 2005a, b, c). An area of over 60 Mha has been deforested in Brazilian Amazonia due to road construction and subsequent new urban settlements (Alves, 2002; Laurance et al., 2005). There is evidence that aerosols from biomass burning may change regional temperature and precipitation south of Amazonia (Andreae et al., 2004) and in neighbouring countries, including the Pampas as far south as Bahía Blanca (Trosnikov and Nobre, 1998; Mielnicki et al., 2005), with related health implications (increases in mortality risk, restricted activity days and acute respiratory symptoms) (WHO/UNEP/WMO, 2000; Betkowski, 2006).

The soybean cropping boom has exacerbated deforestation in Argentina, Bolivia, Brazil and Paraguay (Fearnside, 2001; Maarten Dros, 2004). This critical land-use change will enhance aridity/desertification in many of the already water-stressed regions in South America. Major economic interests not only affect the landscape but also modify the water cycle and the climate of the region, in which almost three-quarters of the drylands are moderately or severely affected by degradation processes and droughts (Malheiros, 2004). The region contains 16% of the world total of 1,900 Mha of degraded land (UNEP, 2000). In Brazil, 100 Mha are facing desertification processes, including the semi-arid and dry sub-humid regions (Malheiros, 2004).

Biodiversity

Changes in land use have led to habitat fragmentation and biodiversity loss. Climate change will increase the actual extinction rate, which is documented in the Red List of Endangered Species (IUCN, 2001). The majority of the endangered eco-regions are located in the northern and mid-Andes valleys and plateaux, the tropical Andes, in areas of cloud forest (e.g., in Central America), in the South American steppes, and in the Cerrado and other dry forests located in the south of the Amazon Basin (Dinerstein et al., 1995; UNEP, 2003a) (see Figure 13.5). Among the species to disappear are Costa Rica’s golden toad (Bufo periglenes) and harlequin frog (Atelopus spp.) (Shatwell, 2006). In addition, at least four species of Brazilian anurans (frogs and toads) have declined as a result of habitat alteration (Eterovick et al., 2005), and two species of Atelopus have disappeared following deforestation (La Marca and Reinthaler, 2005). Deforestation and forest degradation through forest fires, selective logging, hunting, edge effects and forest fragmentation are the dominant transformations that threaten biodiversity in South America (Fearnside, 2001; Peres and Lake, 2003; Asner et al., 2005).

Coral reefs and mangroves

Panama and Belize Caribbean case studies illustrate, in terms of inter-ocean contrasts, both the similarities and differences in coral-reef responses to complex environmental changes (Gardner et al., 2003; Buddemeier et al., 2004). Cores taken from the Belizean barrier reef show that A. cervicornis dominated this coral-reef community continuously for at least 3,000 years, but was killed by white band disease (WBD) and replaced by another species after 1986 (Aronson and Precht, 2002). Dust transported from Africa to America (Shinn et al., 2000), and land-derived flood plumes from major storms, can transport materials from the Central American mainland to reefs, which are normally considered remote from such influences, as potential sources of pathogens, nutrients and contaminants. Human involvement has also been a factor in the spread of the pathogen that killed the Caribbean Diadema; the disease began in Panama, suggesting a possible link to shipping through the Panama Canal (Andréfouët et al., 2002). Since 1980 about 20% of the world’s mangrove forests have disappeared (FAO, 2006), affecting fishing. In the Mesoamerican reef there are up to 25 times more fish of some species on reefs close to mangrove areas than in areas where mangroves have been destroyed (WWF, 2004).