Source: Intelligent Living
“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, the majority of scientists have never heard about it before. But it has become a cause of concern today and several scientists are working on it.”
Global Dimming: Causes & Effects
Global dimming refers to the gradual reduction in the amount of global hemispherical irradiance(or total solar irradiance) present at the earth’s surface or the reduction in the amount of heat reaching the earth is known as global dimming.
Though the actual cause of global dimming is yet to be ascertained, 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 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 from penetrating. Few experts say it's due to air pollution. Global dimming creates a cooling effect that may have partially masked the effect of greenhouse gasses on global warming.
Fossil Fuel use as well as producing greenhouse gases creates other by-products which are also pollutants such as sulfur dioxide, soot, ash, etc.
These pollutants however also change the properties of clouds. Clouds are formed when water droplets are seeded by air-borne particles like pollen. Polluted air results in clouds with larger numbers 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 thought 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 become nuclei for cloud droplets also. Increased pollution, resulting in more particulates, create clouds consisting of a greater number of smaller droplets, which in turn makes them more reflexive, therefore bouncing more sunlight back into space.
Clouds intercept both heats from the sun and heat radiated from the earth. Their effects are complex and vary in time, location and altitude.
Generally, in the daytime the interception of sunlight predominates, further giving a cooling effect whereas at night the re-radiation of heat to the earth slows down the earth’s heat loss. The impact of global dimming itself can be devastating. The death toll that global dimming may have already caused is thought to be massive.
Scientific Research on Global Dimming
Scientists claimed that the impact of global dimming would be experienced not in millions but billions. The Asian monsoons bring rainfall to half the world’s population. Air pollution and global dimming might have a detrimental impact on the Asian monsoons which might leave some 3 billion people affected.
It has also been concluded that imbalance between global dimming and global warming at the surface leads to weaker turbulent heat fluxes in the atmosphere.
This means globally reduced evaporation and hence precipitation occurs 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 from global warming, according to a report in nature.
There exists massive evidence supporting the fact that the world is getting warmer. But it’s also getting 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. As per the research made so far 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 becomes the winner but in the end, the sufferer is and will be the human being.
Written by- Devika Thapar
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