Atmospheric Degradation and Climate Variability

e atmosphere is the essential physical and chemical environment for land-based life, including a significant proportion of the biosphere on which human life depends. Changes to the physical and chemical properties of the atmosphere have the potential of directly or indirectly affecting the quality of life and even the very existence of some forms of life (WMO, 2000).

Africa contributes very little to global climate change, with low carbon dioxide emissions from fossil fuel use and industrial production in both absolute and per capita terms. Africa accounts for 2-3 per cent of the world’s carbon dioxide emis-sions from energy and industrial sources, and 7 per cent of emisemis-sions from land use (forests) are taken into account (UNECA, 2002a). South Africa is by far the largest emitter of carbon dioxide in Africa. e country is responsible for about 39 per cent of the continent’s total emissions. South Africa’s per capita carbon dioxide emissions (1.88 tons) are higher than the global average of 1.13 tons a year. More than 90 per cent of South Africa’s electricity is generated from the combustion of coal that contains approximately 1.2 per cent sulphur and up to 45 per cent ash. Coal combustion can lead to particulate matter in the air and contribute to acid rain. It is estimated that around 2,000 children die annually as a result of respiratory infections caused by air pollution, the sixth largest killer of children under four in South Africa.

In addition to industrial pollution, low-level atmospheric pollution often results from coal combustion in stoves, as well as coal-heated boilers that are found in

hospitals and factories. Vehicular emissions, while not nearly as significant in absolute terms as in cities such as New York, Tokyo or Los Angeles, nonetheless have a negative impact on the environment. Studies in 1990-1996 found that Zimbabwe is a greenhouse gas sink. ough the energy sector in Zimbabwe is a major emitter of greenhouse gases, the country’s forests are able to absorb far more gases than the quantity that all other sectors emit (ENDA, 1997).

In Southern Africa, the main environmental issues of concern, regarding atmos-pheric degradation are the occurrence of flooding and droughts. ese arise from climate variability, impacts of climate change on vegetation systems, biodiversity, freshwater availability, food production and localized air quality problems associ-ated with emissions from industry, vehicles and use of domestic fuels. Droughts, cyclones, floods, and bushfires have brought untold hardship to millions of people.

Rainfall in Southern Africa is strongly influenced by the Inter-Tropical Con-vergence Zone (ITCZ), a zone close to the equator where massive rain-bearing clouds form when the South East Trade Wind (from the south east of the conti-nent) meets the North East Monsoon Winds. e ITCZ changes position during the year, oscillating between the Equator and the Tropic of Capricorn, and its southward movement usually marks the beginning of a rainy season. e further south the zone moves, the more promising this is considered to be for the rainy season. In a normal season, the ITCZ can exert an influence between mid- Tan-zania and southern Zimbabwe and is associated with favourable rainfall. Another system, the Botswana High, often tends to push the ITCZ away, resulting in periods of drought.

ENSO also influences Southern Africa’s climate, tending to bring either heavy rains often accompanied by severe floods, as in 1999/2000 when Mozambique was exceptionally hard hit, or drought, as in 1982-1983 when much of Southern Africa was severely affected. In the wet season, normal rainfall ranges from 50 mm to over 1000 mm. Recent weather patterns have been erratic with severe droughts recorded in 1967-1973, 1981-1983, 1986-1987, 1991-1992 and 1993-1994.

Floods have also been observed, most notably across most of Southern Africa in 1999-2000 (WMO 2000).

e drought of 1991-1992 was the severest on record, causing a 54 per cent reduc-tion in the cereal harvest and exposing more than 17 million people to the risk of starvation. Zimbabwe alone imported an additional 800,000 tons of maize, 250,000 tons of wheat, and 200,000 tons of sugar (Makarau 1992). Water and electricity shortages resulted in a 9 per cent reduction in manufacturing output and a 6 per cent reduction in foreign exchange earnings (Benson & Clay 1994).

e potential effect of climate change on drought in Africa is uncertain. At a local level, increased temperatures are likely to lead to increased moisture demand. e

balance between rainfall and higher evapo-transpiration implies more frequent water scarcity. However, a great deal depends on vegetation response to higher CO₂ concentrations and the timing of rainfall. e combination of higher evapo-transpiration and even a small decrease in precipitation could lead to significantly greater drought risks. An increase in precipitation variability would compound temperature effects. For example, Hulme (1996b) reports that inter-annual vari-ability increases on the order of 25 per cent in much of southern Africa in the transient scenario (UKTR) for the 2050s.

Within the sub-region, some areas experience a similar decrease in variability. e temperature-precipitation-CO₂ forcing of seasonal drought is less significant than the prospect of large-scale circulation changes that drive continental droughts that occur over several years. A change in the frequency and duration of atmos-phere-ocean anomalies, such as the ENSO phenomenon, could force such large-scale changes in Africa’s rainfall climatology. However, such scenarios of climate change are not well developed at the global level, much less for Africa.