ECONOMIC IMPACT OF ENVIRONMENTAL DEGREDATION
4. CLIMATE CHANGE
agriculture (Hulme, 1996a). In addition, declining human health affects labour productivity in agriculture.
Ultimately, climate change is a global issue - even more so for traded commodi-ties such as agricultural products. Some regions, for example, may be less com-petitive in national and global agricultural markets, with corresponding impacts on exports and imports. Africa, in particular, may be sensitive to changes in world prices and stocks because many countries rely on food imports. Several world-trade models have been tested with climate-change scenarios, with differ-ing assumptions regarddiffer-ing economic growth, population growth, trade liberaliza-tion, and technological innovation (Fischer et al., 1994, 1996; Rosenzweig and Parry, 1994). Because they are global simulations, they can illustrate some of the dynamic adjustments in world prices and regional imports and exports that may result from climate change.
However, Africa is not well represented in such assessments. Scenarios tend to be trend projections that discount the potential for dramatic improvements in agricultural welfare. Moreover, the lack of uniform and accessible data on crop-climate sensitivity in Africa leads to large uncertainties in the predicted impact on Africa. A critical question is the extent to which climate change, at the global level, alters African exports (reflecting changes in comparative advantage) and food imports (reflecting the world price of cereals).
4.2 Forestry and Climate Change
Plantations may be most vulnerable to climate change through increased stress resulting from drought, which makes conditions ideal for new or old pests and diseases. In a matter of a few years, an important species can be wiped out before control measures are developed or new species found to replace it. No data exist on how plantation species in Africa may respond to increases in carbon dioxide concentrations. It would seem likely that improved WUE associated with carbon dioxide fertilization effect could boost productivity.
4.3 Fisheries Resources and Climate Change
e vulnerability of fisheries to climate change depends on the nature of the climate change, the nature of the fishery, and its species and habitats. Changes in climatic conditions such as air temperature and precipitation affect fisheries by altering habitat availability or quality. Specifically, fisheries habitats may be affected by changes in water temperature; the timing and duration of extreme temperature conditions; the magnitude and pattern of annual stream flows;
surface-water elevations; and the shorelines of lakes, reservoirs, and near-shore marine environments (Carpenter et al., 1992).
Mean annual air temperature is the most important factor in predicting lake-fish production across latitudes. Alterations in seasonal climate patterns should change the population distributions in larger lakes. Large lake-fish production could increase by about 6 per cent with a 1°C rise in average annual air tempera-ture (Meisner et al., 1987; IPCC 1996, WG II, Section 16.2.1). Warm-water lakes generally have higher productivity than cold-water lakes, and existing warm-water lakes are in areas with the least change in temperature. It is reason-able to expect higher overall productivity from freshwater systems.
Although changing rainfall patterns and flood regimes may have profound effects on freshwater fish, marine fisheries are likely to be affected more by elevated temperatures (Hernes et al., 1995). e impact of elevated temperatures could include a shift in the centre of production. It could also affect the composition of fish species as ecosystems move geographically and change internally. is is in contrast to freshwater fish species, particularly in small, shallow rivers and lakes, which will have limited possibilities for adapting to the changes through migra-tion. Economic values can be expected to fall until long-term stability is re-estab-lished. Rapid changes resulting from physical forcing favour smaller, low-priced, opportunistic species that discharge large numbers of eggs over long periods.
Where ecosystems shift position, national fisheries will suffer if institutional mechanisms are not in place to enable fishermen to move within and across present exclusive economic zone boundaries. Subsistence and other small-scale fishermen (who dominate in Africa) will probably suffer disproportionately from such changes (Everett, 1994). A reduction in fish stocks will have the greatest effect on countries such as Namibia that are heavily dependent on fisheries and cannot diversify easily into other activities.
4.4 Coastal Zones and Climate Change
Climate change will exacerbate existing physical, ecological/biological, and socio-economic stresses on the African coastal zone. Most existing studies focus on the extent to which rising sea levels could inundate and erode low-lying areas or increase flooding caused by storm surges and intense rainstorms. e coastal nations of west and central Africa (e.g., Senegal, e Gambia, Sierra Leone, Nigeria, Cameroon, Gabon, Angola) have low-lying lagoonal coasts that are sus-ceptible to erosion and would be threatened by sea-level rise.
Most of the countries in this area have major and rapidly expanding cities located on the coast (IPCC, 1996). Africa’s west coast is often buffeted by storm surges and is currently is at risk from erosion, inundation, and extreme storm events. Inunda-tion can be a significant concern and major cities situated at sea level would be very vulnerable. Moreover, tidal waves, storm surges, and hazards may also increase and possibly modify littoral transport (Allersman and Tilsmans, 1993).
Sea level rise as a result of global climate change would cause inundation of the extensive mangroves of Mozambique and Tanzania and these would retreat, thus increasing rates of erosion on the shoreline. e coastal lagoons of Angola would also be inundated. Sea level rise is also a major threat to low-lying coastal urban centres and ports, such as Cape Town, Maputo, and Dar-es-Salaam. Its impact could result in loss of income from coastal industries and port activities through-out the sub-region, and loss of opportunities for development of tourism (IPCC 1998).
In Tanzania, a sea level rise of 0.5 m would inundate over 2 000 km2 of land, cost-ing around $US 51 million and a rise of 1.0 m would inundate 2 100 km2 of land and erode a further 9 km2, resulting in costs of more than $US 81 million (IPCC 1998). e coral reefs off the coasts of Mozambique, South Africa and Tanzania are under threat of bleaching due to sea temperature rise resulting from El Niño events and global climate change. In 1998, the El Niño induced sea temperature rise of around 1°C causing the death of up to 90 per cent of the corals in the sub-region (Obura et al., 2000).