On January 15, 2005, the BBC broadcast its weekly acclaimed Horizon documentary. This one was about a dangerous phenomenon called Global Dimming.

This reduction of heat reaching the earth is known as Global Dimming.

Clouds are formed when water droplets are seeded by air-borne particles, such as pollen. Polluted air results in clouds with larger number of droplets than unpolluted clouds. This then makes those clouds more reflective. More of the sun’s heat and energy is therefore reflected back into space.

Fossil fuel use, as well as producing greenhouse gases, creates other by-products. These by-products are also pollutants, such as sulphur dioxide, soot, and ash. These pollutants however, also change the properties of clouds.

Impacts of global dimming: millions already killed by it?

Global warming results from the greenhouse effect caused by, amongst other things, excessive amounts of greenhouse gases in the earth’s atmosphere from fossil fuel burning. It would seem then, that the other by-products which cause global dimming may be an ironic savior.

A deeper look at this, however, shows that unfortunately this is not the case.

Health and environmental effects The pollutants that lead to global dimming also lead to various human and environmental problems, such as smog, respiratory problems, and acid rain. The impacts of global dimming itself, however, can be devastating.

Millions from Famines in the Sahel in the 70s and 80s The death toll that global dimming may have already caused is thought to be massive. Climatologists studying this phenomenon believe that the reflection of heat have made waters in the northern hemisphere cooler. As a result, less rain has formed in key areas and crucial rainfall has failed to arrive over the Sahel in Northern Africa. In the 1970s and 1980s, massive famines were caused by failed rains which climatologists had never quite understood why they had failed. The answers that global dimming models seemed to provide, the documentary noted, has led to a chilling conclusion: what came out of our exhaust pipes and power stations [from Europe and North America] contributed to the deaths of a million people in Africa, and afflicted 50 million more with hunger and starvation.

Billions are likely to be affected in Asia from similar effects Scientists said that the impact of global dimming might not be in the millions, but billions. The Asian monsoons bring rainfall to half the world’s population. If this air pollution and global dimming has a detrimental impact on the Asian monsoons some 3 billion people could be affected.

As well as fossil fuel burning, contrails is another source Contrails (the vapor from planes flying high in the sky) were seen as another significant cause of heat reflection. During the aftermath of the September 11, 2001 terrorist attacks in the United States, all commercial flights were grounded for the next three days. This allowed climate scientists to look at the effect on the climate when there were no contrails and no heat reflection. What scientists found was that the temperature rose by some 1 degree centigrade in that period of 3 days.

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