This page was written in 2005 so very dated. You might read the relevant article on Wikipedia for a more up to date perspective.
Contact: David K. Clarke – ©
The effect was first noticed by an English scientist, Gerry Stanhill, working in Israel. When he compared Israeli sunlight records from 1950 with more recent ones he found that there was "a staggering 22% drop in the sunlight". Recently Australian scientists confirmed Stanhill's finding using completely different methods; they were looking at the decline in evaporation rates from meteorological pans. The dimming appears to be mainly caused by increasing amounts of air pollution, largely associated with smoke and the burning of fossil fuels.
Aircraft contrails are responsible for some global dimming. (All commercial flights were stopped for a few days following the New York Twin-Towers 2001/09/11 incident. Researchers discovered some unexpected changes associated with the sudenly greatly reduced contrail density.) Contrails also decrease the diurnal temperature variation; that is, they cause nights to be a little warmer and days to be a little cooler than they would otherwise be.
The dimming of sunlight may well cause reduced evaporation from the oceans with consequent reduction in rainfall. There have been suggestions that the effect may be responsible for droughts in the Sahel in the 1970s and 1980s. It may also have a disastrous impact on Asian monsoons.
Research has indicated that since 1950 the USA has lost 10% of its sunlight, the British Isles 16%, and some states of the former USSR over 30%. The largest reductions have taken place in northern hemisphere mid latitudes.
Perhaps the most worrying aspect of global dimming is that, in spite of
the dimming we have been seeing rising world temperatures ascribed to
global warming and the man-made greenhouse effect. If the greenhouse
effect is sufficient to counteract global dimming and raise world
temperatures the obvious conclusion is that the anthropological
greenhouse effect is even greater than has been thought.
Nations like the USA and Australia have been very irresponsible in their failure to limit the damage they are doing in greenhouse. Is there any reason to think that they are likely to do better in their responsibility to fix the global dimming - greenhouse combination now that it has been discovered?
Climate change due to Man's actions is a far greater risk to the
world than is terrorism.
Unless great public pressure is placed on the governments of Australia
and the USA to 'clean up their act' the situation is only going to get
Late southern summer of 2020Unprecedented Australian fires in the southern summer of 2019-2020 put huge quantities of smoke into the atmosphere, even into the stratosphere. (See Washington Post article).
Some of the smoke in the stratosphere circled the earth several times. It reduced the amount of the Sun's heat reaching ground level in the later part of the southern summer, resulting in lower than usual temperatures.
While the smoke temporarily reduced the temperature the huge amount of carbon dioxide that the fires added to the atmosphere will have the long-term effect of increasing temperatures - and increasing the frequency and ferocity of future fires.
Global dimmingA good site for more detail on the problem is BBC.
A page from the Australian Greenhouse Cooperative Research Council's site gives a list of research papers on the subject.
There is an extensive entry on the subject in
Fires and smokeFierce, frequent, climate-fueled wildfires may decimate forests worldwide; NBC News, 2020/09/22.
Climate change boosted Australia bushfire risk by at least 30%; BBC news, 2020/03/04