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ARTICLE : Global Dimming
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Wednesday, 17 July 2013 04:13

Global Dimming

“Each year less light reaches the surface of the Earth. No one is sure what’s causing ‘global dimming’ or what it means for the future. In fact most scientists have never heard of it. But it has become a cause of concern today and several scientists are working on it.”

What is Global Dimming

Global dimming is the gradual reduction in the amount of global hemispherical irradiance (or total solar irradiance) at the Earth’s surface or in other words the reduction of heat reaching the earth is known as Global dimming.

Causes and Effects

Though the actual cause of Global dimming is yet ascertain yet some scientists think that it’s nothing to do with changes in the amount of radiation arriving from the sun. although that varies as the sun’s activity rises and falls and the Earth moves closer or further away, the global dimming effect is much, much larger and the opposite of what would be expected given there has been a general increase in overall solar radiation over the past 150 years.

That means something must have happened to the Earth’s atmosphere to stop the arriving sunlight penetrating. The few experts who have studied the effect believe it’s down to air pollution. Tiny particles of soot or chemical compounds like sulphates reflect sunlight and they also promote the formation of bigger, longer lasting clouds. “The cloudy times are getting darker”, says Cohen, at the Volcani Centre. “If it’s cloudy then it’s darker, but when it’s sunny things haven’t changed much”.

Global dimming creates a cooling effect that may have partially masked the effect of greenhouse gases on global warming. 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. 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 reflexive. More of the sun’s heat and energy is therefore reflected back into space.

It is currently though that the effect of Global dimming is probably due to the increased presence of aerosol particles in the atmosphere. Aerosol particles and other particulate pollutants absorb solar energy and reflect sunlight back into space. The pollutants can also become nuclei for cloud droplets. It is though that the water droplets in clouds coalesce around the particles. Increased pollution, resulting in more particulates, creates clouds consisting of a greater number of smaller droplets, which is turn makes them more reflective, therefore bouncing more sunlight back into space.

Clouds intercept both heat from the sun and heat radiated from the Earth. Their effects are complex and vary in time, location and altitude. Usually during the daytime the interception of sunlight predominates, giving a cooling effect; however, at night the re-radiation of heat to the Earth slows the Earth’s heat loss.

The impacts of Global dimming itself, however, can be devastating. Millions from Famines in the Sahel in the 70s and 80s.  The death tool that Global dimming may have already caused is thought to be massive.


Climatologists studying this phenomenon believe that the reflection of heat have mae 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.

It is also concluded that the imbalance between global dimming and global warming at the surface leads to weaker turbulent heat fluxes to the atmosphere. This means globally reduced evaporation and hence precipitation occur in a dimmer and warmer world, which could ultimately lead to a more humid atmosphere in which it rains less.

This phenomenon of ‘Global dimming’ is now being accepted as a reality by scientists the world over. Some of them believe that this may help in protecting the planet form Global warming, according to a report in the Nature. There’s massive evidence that the world is indeed getting warmer. But it’s also getting’s darker. In fact, many scientists believe that Global dimming puts the brakes on the warming of our planet. Without Global dimming, global warming would be much, much worse!

And there’s no telling which will win in the end, heat or cold. Roughly speaking, Global dimming is faster and heftier, while global warming is slower and more gradual. Somewhere down the line, there could be a threshold, a point where Dimming beats Warming or Warming beats Dimming. Whosoever be the winner the sufferer in the human being.


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