Global warming (also called the greenhouse effect) describes the gradual increase of the air temperature in the earth's lower atmosphere.
A greenhouse is made entirely of glass. When sunlight (shortwave radiation) strikes the glass, most of it passes through and warms up the plants, soil and air inside the greenhouse. As these objects warm up they give off heat, but these heat waves have a much longer wavelength than the incoming rays from the sun. This longwave radiation cannot easily pass through glass, it is re- radiated into the greenhouse, causing everything in it to heat up.
THE NATURAL GREENHOUSE EFFECT
The term greenhouse effect is used to describe the warming effect that certain gases have on the temperature of the earth's atmosphere under normal conditions.
Sunlight (shortwave radiation) passes easily through the earth's atmosphere. Once it strikes and warms the earth's surface, longwave radiation is given off and goes back into the atmosphere. While some of this longwave radiation or heat escapes into space, most of it is absorbed or held by carbon dioxide and other gases that exist in small quantities in the atmosphere. Thus these gases form a `blanket' that keeps the earth an average of 33 degrees centigrade warmer than it would be if this greenhouse effect did not occur. Without these gases the whole planet would be an icy wasteland with an average temperature of 16 degrees centigrade below freezing!
HOW HAVE PEOPLE ALTERED THE GREENHOUSE EFFECT?
Human population growth and related industrial expansion, have led to greater air pollution and a change in the composition of the earth's atmosphere. Some pollutants enhance the natural greenhouse effect, resulting in increased global atmospheric temperatures.
DID YOU KNOW?
* Many nations are reluctant to commit themselves to the costly changes necessary to reduce greenhouse gas emissions in view of the uncertainties surrounding the precise effects of global warming.
* Atmospheric CO2 concentration will be double the pre- industrial concentration in about 60 years time.
* Sea levels are likely to rise 60 mm each decade over the next century.
* Two-thirds of South Africa's population rely mainly on coal as an energy source. Providing electricity to these people will result in a nett reduction in CO2 emissions as a consequence of improved overall energy efficiency.
WHAT WE CAN DO
Reduction of greenhouse gas emissions requires greater energy efficiency. Industrialists and governments have a key role to play here. But what can the individual do?
- Reduce electricity consumption.
- Use lift clubs, public transport, bicycles or your feet for transport.
- Reduce, reuse, recycle, and save energy - the manufacture of all products requires energy.
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