17 January 2005

Climatologists predict a very dry SA future

Global warming is already here - and as it gains momentum southern Africa can expect to get less and less rain in the years ahead, according to a climatologist.

University of Pretoria meteorology scientist Francois Engelbrecht said: "Industrialised countries are not doing enough to cut back on greenhouse gases and the effect on the southern African region will be devastating. Even if industrial countries stopped producing greenhouse gases, it would take many a year to turn around the effects of global warming."

Engelbrecht said research showed that a high-pressure system had formed over much of southern Africa, fed by air that had been heated by greenhouse gases over the equator.

"The hot air rises about 15km into the air above the equator. [It] cannot escape into the atmosphere and is forced in a northerly and southerly direction.

"The air that is pushed southward towards South Africa is then diverted westward because of the rotation of the Earth and is piled up as a huge subtropical high-pressure belt over central South Africa.

"This pressure belt that has been growing in strength because of the mass inflow of air that rises at the equator is the key to climate changes in this country.

"The high-pressure belt pushes the cold fronts further and further south during the winter season and that is why the Cape is getting less and less rain. In fact, in future that region may have to look at changing its agricultural products to handle the drier weather."

But it is not only the Western Cape that are looking at less and less rain as global warming takes effect.

"During the summer months the high-pressure system is broken up and pushed eastward," Engelbrecht said.

"This means that areas such as the Free State, Gauteng and Mpumalanga and other summer rainfall areas will also be getting less rain and become drier and drier.

"Ironically, there is a belt across the Northern Cape and central parts of Eastern Cape that has been getting wetter over the past 40 years [the period during which other areas have been getting drier].

"However, this belt of wet weather will continue to be pushed westward as the high-pressure belt continues to grow. Eventually the wet belt will be pushed out towards the Atlantic. By that time the cold fronts bringing rain will have been pushed even further to the south of the Cape.

"Unless greenhouse gas emissions can be radically cut, we don't see this scenario changing, and there is very little chance that industrial countries will cut back emissions. It is going to get worse and the southern African sub-continent is going to get very dry."

University of Cape Town climatology professor Bruce Hewitson said global warming and its effects could no longer be credibly denied.

"We no longer have a normal climate. The climate is in transition and one can expect an increase in the frequency of extreme weather events.

"The occurrence of extreme weather events such as the flooding in the United Kingdom is indicative of global warming," he said.

"Global warming adds energy to the Earth and atmosphere and, with more energy, weather events are more intense."

Across the world, extreme climatic conditions - for example the severe floods in Britain and the United States, extreme heatwaves in Europe last year and an increase in the incidence and strength of hurricanes in North America - appear to be fulfilling predictions made years ago about a warmer planet.


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