Wednesday, March 08, 2006


Global-dimming is the process whereby solar radiation is prevented from reaching the earth's surface by aerosols such as soot and dust. Air transport is a major player in global dimming due to the fact that it releases many aerosols in the troposphere. This was proved when there was a 1ÂșC increase in the U.S after 9/11 due to the inactivity of airplanes for only three days. Subsequently, reports indicate that the rate of dimming is increasing at 2-3% per decade, worldwide. The aerosols either block or reflect large amounts of sunlight. Hence, in Israel there was a notable decrease in evaporation. Aerosols also affect cloud formation due to excessive precipitation around particles.

Global-dimming is a factor that should be taken very seriously for a number of reasons. It is a factor that counter-balances the effects of global-warming. This means that as climate is warming due to the emission of greenhouse gasses there is the directly proportional effect of global-dimming. An inevitable question is: "What if emissions are decreased? Will the decrease in global dimming, cause excessive warming? Or vice-versa.

The impacts on natural processes (e.g. decreased energy) could be devastating. Excessive drought, which is evident in the Sahel area, is due to the inefficient movement of air from the tropics to temperate regions. This is a death sentence for impoverished people living in that area.

Hence it is clear that various questions and factors concerning global-dimming need to be taken seriously.

Dane McDonald
Department of Biodiversity and Conservation Biology
University of the Western Cape
Private Bag X17
Bellville 7535


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