Driving forces affecting climatic and atmospheric change

The direct causes of atmospheric change and the enhanced greenhouse effect are human activities such as the burning of fossil fuels and the clearing of natural vegetation for agricultural purposes. The level of these human activities is influenced by population size (see social), income (and therefore consumption) level and distribution between rural and urban locations, and national and other policies regarding economy, energy, land use and development. Figure 1.1 explains these influences.

Figure 1.1 Flow diagram of the drivers of climatic and atmospheric change

These activities emit a variety of gases, the most important of which are carbon dioxide, methane and nitrous oxide (which cause global warming); nitric oxide and volatile organic compounds (which react with methane and sunlight to form ozone, a greenhouse gas and toxic substance when in the lower atmosphere, but a beneficial screen against ultra-violet radiation in the upper atmosphere); sulphur dioxide and dust and smoke particles (which help to reduce global warming). Sulphur dioxide and nitric oxide are deposited as acids, which are corrosive and harmful in the long term to ecosystems as certain plant and animal species are very sensitive to changes in soil and water acidity. Acidification of surface water also makes it less suitable for drinking, irrigation, and industrial uses. Certain gases gases, such as the ozone-depleting chlorofluorocarbons (CFC's), find their way to the upper atmosphere, where they destroy beneficial ozone.

These human causes are overlaid on the complex and poorly-understood workings of the global climate system.  For instance, the climate of southern Africa is strongly influenced by the El Niño-Southern Oscillation (ENSO), a global phenomenon caused by a large difference in temperature in the eastern Pacific Ocean.  During ENSO  events the summer rainfall areas are abnormally dry. The Indian and Atlantic oceans which are adjacent to the African continent also have a strong influence on South Africa's climate, most of the rainfall coming from the warmer east coast of the Indian Ocean.

South Africa was responsible for about 1.2% of the total global warming effect in 1990 which placed it within the top ten contributing countries in the world. The carbon dioxide equivalent emission rate per person in South Africa (about 10 tons of carbon dioxide equivalent per person per year) is above the global average of about 7 tons per person per year. This is about twice as much as other developing countries such as Mexico, Argentina, Zimbabwe and Algeria (which emit less than 5 tons of carbon dioxide per person per year). However, Mexico and Nigeria have significant domestic oil reserves and are thus able to use oil as their primary energy source. Argentina has large natural gas reserves. When gas is combusted it produces less metuane and nitrous oxide, per unit of energy, than coal. Zimbabwe uses a fair proportion of coal per power generation but also taps the hydropower capacity of the Zambezi river. South Africa is almost totally dependent on domestic coal reserves as the primary energy source. It is also important to note that these emission rates are considerably below that of developed countries such as the United States of America (over 20 tons per person per year)  (Bach and Jain, 1991). The main gases emitted and contributing to the global warming) effect from South Africa, weighted by their global warming potential (GWP) over a 100 year period are carbon dioxide (81%), methane (13%) and nitrous oxide (6%). (Source: South African Country Study, unpublished report).

The trends in coal and oil consumption (the main sources of energy in South Africa) consumption and the conversion of natural vegetation to agricultural crops are provided in figures 1.2 and 1.3 respectively.  Total consumption of coal and oil (or its derivative, petroleum) and the surface area converted for agricultural purposes on a yearly basis are indicators for the increase or decrease in greenhouse gas emissions.

Figure 1.2 Trends in oil and coal consumption

Figure 1.2 Trends in oil and coal consumption Fossil fuel  burning is the main source of carbon dioxide, which is currently responsible for more than 60%  of the enhanced greenhouse effect. Methane is responsible for 20% and nitrous oxide, CFC's Chlorofluorocarbons and ozone together contribute the remaining 20%. Water vapour is the largest contributor to the natural greenhouse effect in South Africa. The values are expressed in energy terms (PJ = Petajoules; IPJ = 10 ¹⁵ Joules). Note that during the 1980's,  due to the international oil embargo against South Africa, coal was substituted for oil as an energy source. After 1988 this trend reversed, with coal consumption going from 150 to 50 PJ/yr, and oil consumption from -25 to 42 PJ/yr . The current growth rate in energy consumption, is approximately 5% per annum, comparable to the trend in other developing countries. (Sources: National Energy Statistics and Addendum, and National Energy Balance http://www.rau.ac.za/english/academic/index.htm. See also http://mbendi.co.za/sapia for petroleum product consumption).

Figure 1.3 Trends in the conversion of natural vegetation to agricultural crops

Figure 1.3 Trends in the conversion of natural vegetation agricultural crops. The conversion of natural vegetation to agricultural crops increased rapidly between 1930 and 1970 due to the widespread availability of tractors, fertiliser and pest control, national land policies, and subsidised prices for farm produce.  South Africa has a limited area of high-quality agricultural land (only 12 % is economically viable for cultivation under current circumstances; see Terrestrial Ecosystems) and since the 1970's there has been only a small increase in area under cultivation (stabilised at around 10,5 million hectares) [see Terrestrial Ecosystems]. Source: Abstract of Agricultural Statistics, Department of Agriculture, 1993

>     Climatic and Atmospheric Change: Pressures

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