National State of the Environment Report - South Africa  
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The State of South Africa's Climate and Atmosphere in the 1990s

The state of climatic and atmospheric change is described under the following headings:
State of the atmosphere
State of the climate: 1990s compared to 1960 - 1989
Sea level rise

State of the Atmosphere:   Top of Page

The trends in atmospheric concentrations (background concentrations) of carbon dioxide, methane, nitrous oxide and CFC-11 are measured at the Global Atmosphere Watch station at Cape Point, which is jointly operated by the South African Weather Bureau and the Fraunhofer Institute for Atmospheric Environmental Research in Germany. This station also measures many other atmospheric substances (Figures 1.4, 1.5, 1.6, and 1.7 show measurements from this station). An index of changes in total atmospheric ozone measured in Pretoria is given in Figure 1.8. The trend in the amount of Ultraviolet-B(UV-B) exposure in Pretoria, measured as the minimum amount of erythema dose (MED) minimum erythema dose is shown in Figure 1.9.

Figure 1.4 Trend in atmospheric concentrations of carbon dioxide as measured at Cape Point.

The overall increase in atmospheric concentrations of carbon dioxide is approximately 0.6% per year in South Africa (Figure 1.4). Increase in CO2 is a global phenomenon which is the subject of much concern and research. The trend is overlaid on a seasonal cycle due to the uptake of carbon dioxide by terrestrial ecosystems during the summer growing period, and release due to respiration in the winter. This is opposite in timing to the northern hemisphere, and much weaker, since the southern hemisphere is mostly ocean. (Source:SAWB. See also CDIAC Trends 91: A Compendium of Data on Global Change. Oak Ridge National Laboratory, 1991).

Figure 1.5 Trend in atmospheric concentrations of methane as measured at Cape Point.

As shown in Figure 1.5, tropospheric methane has increased steadily from 1983 to 1998 (total increase of 8.3% over the time period). The annual growth rate decreased between the 1980s and early 1990s. It is thought to be due to the combined effects of an event and the Pinotubo volcanic eruption, which cooled and dried the tropics. Tropical wetlands and rice fields are a major global methane source although none are found in South Africa. (Source:SAWB). The growth rate started to increase again from 1996 onwards. It remains to be seen, whether this is only a temporary feature related to the El Niño phenomenon or whether it constitutes a long-term increase in the methane growth rate for the Southern Hemisphere.

The increases in concentration of nitrous oxide at about 0.2% per year as shown in Figure 1.6 is largely due to nitrogen fertiliser use in other parts of the world, but this is currently not of concern locally and internationally. (Source: SAWB)

Figure 1.6 Trend in atmospheric concentrations of nitrous oxide as measured at Cape Point.

Figure 1.7 clearly shows the international success achieved in phasing out ozone depleting compounds after the implementation of the Montreal Protocol in 1987. The concentration of this long-lived gas will continue to decline gradually, and the impacts on the ozone layer will slowly disappear. (Source: SAWB)

Figure 1.7 The time series for CFC-11 as measured at Cape Point.

In figure 1.8, an index of changes in the total atmospheric ozone as measured at Pretoria is shown. The values are expressed as anomalies, in other words, as differences above and below the long-term mean of 274 Dobson Units.

The main fluctuation is within each year, caused mainly by natural seasonal cycles in the stratosphere but with a small contribution from seasonal increases in lower atmosphere ozone largely due to veld fires and other natural processes. There is no overall trend between years at this location. (Source SAWB Dobson spectrophotometer #89, Irene).

Figure 1.8 An index of changes in the total atmospheric ozone, as measured at Pretoria

Figure 1.9 a-c shows the amount of UV-B measured as the minimum erythema dose in Pretoria, Cape Town and Durban from 1994 until 1998. For almost half the year, (MED) minimun erythema dose levels fall within the dangerous to very dangerous categories for all 3 cities.

The amount of UV_B measured as the minimum erythema dose in Pretoria The amount of UV_B measured as the minimum erythema dose in Cape Town
Figure 1.9a-b The amount of UV_B measured as the minimum erythema dose in Pretoria, Cape Town
The amount of UV_B measured as the minimum erythema dose in Durban

January and December show the highest levels. No trend for Pretoria or Cape Town is apparent. The apparent downward trend in Durban may be due to year-to-year differences in cloud cover and surface pollution. It is unlikely to be caused by changes in the ozone layer as it is not consistent with the other sites.

Figure 1.9c The amount of UV_B measured
as the minimum erythema dose in Durban.

The extreme seasonal pattern in Cape Town is due to the clear summer skies and cloudy winters, superimposed on the seasonal variation in solar altitude and day-length. Zero values are due to instrument failure. The seasonal pattern is due to the reflection of UV-B back into the atmosphere by clouds during the rainy season. (Source: SAWB).

The concentration of sulphur dioxide is in principle measured at many stations in all the major urban areas in South Africa. In practice, many of these stations are not operational due to financial contraints. Table 1.3 contains data from a site in Middelburg, an urban location in the major industrial and energy generation region of the country. Analysis of sulphur dioxide trends over all the available sites is given in Figure 1.10 (Van Zyl and Kruger, 1998)

Table 1.3 Highest SO2 concentrations measured in the National Smoke and SO2 network (April 1997-March 1998) (Source: Van Zyl and Kruger, 1998).
Place Monthly Averages (µg/m3)
Middelburg Central Business District 31-134
Middelburg: Weber Street, Industrial 17-140
Middelburg: Fontein Street , Residential 37-112

The highest average SO2 concentrations measured in the national network for smoke and SO2 ( April 1997-March 1998) was at Middelburg . The guideline concentration (set by the World Health Organisation, from a health perspective) which should not be exceeded for a period of more than 24 hours, is 125 µg/m3 (48 ppb).The highest single recording for the same time period was 1600 µg/m3 (611 ppb), measured at Thebelisha, Springs. In general, the worst air quality in South Africa occurs when wood, dung or coal is used as fuel inside poorly-ventilated dwellings, in informal settlements and rural villages. The most recent study on the use of coal for cooking (which is common in South Africa) was conducted in Qalabotjha, a rural area in the Free State during the winter of 1997. Concentrations of SO2up to 5200 µg/m³ (2 ppm) for 1 hour periods were measured indoors during cooking with coal. The concentrations of total suspended particulate matter measured indoors at Qalabotjha reached 1420 µg/m³ over 5 hours. The minimum levels for effects on human health (decreasing lung function) from total suspended particulate matter were judged to be 180 µg/m³ in the presence of SO2 over a 24 hour period (WHO) World Health Organisation, 1987). (See Social for levels of respiratory ailments in South Africa)

Sulphur dioxide levels are shown if Figure 1.10. These sites are classified as being in industrial areas, commercial business districts or residential areas. More sites have shown decreases in sulphur dioxide concentration than increases, but most show no trend. This suggests that overall, the state of the atmosphere in South Africa with respect to sulphur dioxide is stable to slightly improving.

Figure 1.10 The number of sulphur dioxide recording sites which have shown increases, decreases and no change in the mean sulphur dioxide level.

Smoke is measured in the National Network on Smoke and SO2as a soiling index, in which a white filter becomes discoloured by dust and smoke particles which it collects (Table 1.4). The current Department of Environmental Affairs and Tourism annual index guideline is 20, which converts to about 100 µg/m3.

Table 1.4 Highest average smoke concentrations measured in the National Smoke and SO2 Network (April 1997- March 1998) (Source: Van Zyl and Kruger, 1998).
Place Highest soiling index detected (S/m3) Annual average Annual guideline soiling index
Sunderland Ridge, Centurion (residential and industrial) 112 56 20
Welkom Municipality (industrial) 272 44 20
White City, Springs (residential) 84 33 20
Fordsburg, Johannesburg (industrial/commercial) 71 25 20

An indicator of the health implications of air pollutants is the exceedance or number of instances when the guideline value has been exceeded over a given time period (long term or short term (Figure 1.11). National data for this indicator are currently not available.

Data from Table 1.4 suggest that for many sites in urban areas, especially those near industrial zones, the concentration of smoke particles in the air is higher than desirable, i.e. higher than the annual guideline.

Figure 1.11 The average concentration of a number of key atmospheric pollutants in major South African cities in 1996. (South African guidelines: particulate matter (PM10) annual average = 60 g/m3 ; SO2 24-h average = 100 ppb; NO2 24-h average = 100 ppb; O3 1-h average = 120 ppb).

Figure 1.11 The average concentration of a number of key atmospheric pollutants in major South African cities in 1996.

The South African guideline exposure levels are not exceeded in any of the locations or for any of the gases. From a WHO guideline perspective, no adverse effects in healthy or sensitive people (such as those who already have respiratory problems) are expected at the SO2 concentrations measured in Cape Town. In Vereeniging and Johannesburg, sensitive individuals are likely to experience effects such as wheezing and shortness of breath, especially during outdoor strenuous activities, WHO (World Health Organisation) ,1999. Recent evaluation of data indicate that hospital admissions for respiratory effects commonly follow monthly and annual PM10 particulate matter levels above 40 µg/m3. (Brunekreef et al, 1995).

South African petrols all contained lead as an additive until February 1996, when unleaded petrol was introduced. The change over is gradual since many vehicles in South Africa are old and not adapted to use unleaded fuels. In 1998, unleaded petrol comprised about 10% of sales. In the Western Cape and Gauteng this value is slightly above 10%, but is as low as 4.7% in the North West Province. The amount of lead used in leaded petrol has also been reduced. Lead concentrations (yearly averages) in major South African cities are shown in Figure 1.12.

There has been a decrease in ambient lead concentrations over the past few years which can be attributed to the decrease in lead concentrations in petrol to 10 µg/d in 1991 (Diab, 1999). The marked changes in the atmospheric lead concentrations are somewhat surprising since the penetration of unleaded fuel into the market is still fairly low.

Figure 1.12 Average lead concentrations per year in major South African cities.
State of the Climate 1990s compared to 1960-1989:   Top of Page

The winter rainfall region experienced above-average rainfall in most years, except 1990 and 1997. Rainfall in the central parts of South Africa is closely linked to El Niño/ La Niña; although exceptions (such as 1997) occur. No gradual rainfall trend for the nineties relative to the climate reference period 1960-1989 can be seen (Figure 1.13). There is thus no evidence, based on this short record of any steady increase or decrease in rainfall in recent times.

Figure 1.13 Annual rainfall deviations during the 1990s relative to the mean annual rainfall for the period 1960-1989.

On average, the temperature stations in South Africa showed an increase of 0.2° C during the 1990s, which is not yet a cause for alarm (Figure 1.14). Some stations (such as Boegoesberg and Warmbad) showed variations which were warmer during El Niño events and cooler during La Niña events. The increase in temperature may be associated with global warming, although it is hard to prove statistically with such a short record.

Figure 1.14 Temperature deviations during the 1990s relative to the 1960-1989 period.
Sea level rise:   Top of Page

The sea level at Port Nolloth is rising at the rate of approximately 1.2 mm/yr (Hughes et al 1991). This is comparable to the rate of rise observed elsewhere in the world, and is attributed to global warming. The sea level is predicted to continue to rise, reaching a level between 0.4 and 0.55 m above the 1990 level by the year 2100 (IPCC 1995). This will cause damage to coastal infrastructure, salt contamination of fresh groundwater near the coast, and threaten the homes of people living in low-lying coastal areas. The number of people living very close to sea level in South Africa is fortunately small, since the coastline in most places is steep, and, in general, sea-level rise is not considered a major concern for South Africa.

Top of Page >     Climatic and Atmospheric Change: Impacts

There is also information about Climatic and Atmospheric Change in the following reports:
Metropolitan reports:
Arrow Cape Metropolitan Council (1998 edition) Arrow Durban Pilot Study
Arrow Greater Johannesburg Metropolitan Council (1999 edition) Arrow Greater Pretoria Metropolitan Council (1999 edition)

   
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Last update: October 1999