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Global Dimming - A trend dangerous than Global Warming

"The twin effects of Global Warming and Global Dimming due to human pollution can be extremely disastrous. While global warming increases temperature due to the greenhouse gases, global dimming reduces sun’s intensity due to solid suspended pollutants. They can cause massive climatic change and catastrophic natural disasters like cyclones, droughts, floods, hurricanes etc."

Pritish Pradhan : January 20, 2009

In 1955, a young British immigrant Gerry Stanhill was working on Israel’s irrigation scheme. His job was to find out, with the help of light-meters, how strongly the sun shone over Israel.

He repeated his experiment in the year 1980. Gerry was stunned over his findings. The observations suggested that the sun shone 22% less brightly over Israel than it did in 1955! He published his results but the scientific community dismissed it as nonsense.

At around the same time Beate Leipert - a graduate climatologist reported the same behaviour over the Bavarian Alps of Germany. What was strange was that two completely different sets of observations in two different parts of the world had come to the same conclusion!

Slowly in the 1990’s interest grew on this phenomenon and it was given a suitable name- ‘Global Dimming’.

The phenomenon was strongly challenged since the temperature of the world is rather increasing due to Global Warming and when the temperature is increasing due to rapid pollution how come the sun is gradually dimming? Temperature in the last 100 years has risen by 0.60° C and may rise by 3.75° C globally this century. This makes the twin effects of global warming and global dimming very contradicting.

In 1995 a $25 million multinational project INDOEX was launched to solve the puzzles of global dimming. Scientists saw that the northern islands of Maldives sit on the path of a stream of dirty air descending from India while the southern islands get fresh air from Antarctica. A major difference in light intensity is also observed between the two. The north islands over which the pollutant layer is 3 km thick received 10% less sunlight than the south. Climatologists understood that there was nothing wrong with the sun but with the earth itself.

A major reason for this effect was found in the change in behaviour of clouds that solid pollutants induce. These solid pollutants are emitted in high quantities by vehicular movement, air traffic, industrial activity etc.  In a cloud small droplets of water condense over microscopic solid particles, which then become heavy and fall as rain. But in polluted areas, the number of suspended solid particles in the air like dust, soot etc is very large and over kilometres thick in the atmosphere, which could block the sunlight.

But a more drastic effect is produced when they interact with water droplets. Tiny particles of water form around them like layers. They may stay on in the atmosphere without falling down and turn the clouds into acting like giant mirrors, which reflect much more sunlight into space than ordinary clouds. These solid pollutants, which increase the volume and intensity of these hybrid clouds, prevent the sunlight from reaching the earth’s surface.

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Since increase in pollution is global, this effect is also global. Over a course of thirty years, intensity of sunlight has fallen by 9% in Antarctica, 10% in the U.S., 11% in India, 16% in England, 20% in Singapore and 30% in Russia!!

In one of the longest conducted experiments on climate change, weather stations around the world have been measuring the rate of evaporation of water everyday since more than a century. Their data has revealed that rate of evaporation is declining with time. The reason is that sunlight plays a more dominant role in evaporation than increase in world temperature. This may cause less rain and its effects on India, a monsoon dependent country, is very harmful.

The twin effects of Global Warming and Global Dimming due to human pollution can be extremely disastrous. While global warming increases temperature due to the greenhouse gases, global dimming reduces sun’s intensity due to solid suspended pollutants. They can cause massive climatic change and catastrophic natural disasters like cyclones, droughts, floods, hurricanes etc.

Today, the desertification of a lush green North African region Sahel, Tunisia has been attributed to global dimming. Droughts in that region killed a million people and affected several million more. Thus the ill effects of this phenomenon are already in the course of causing devastation to the life and economy of the world.

After 9/11 attacks, all flights in the U.S.A. were grounded for three days. Dr. David. Gerard, University of Wisconsin studied its effects. He found that in just 3 days temperatures rose 1° C. It happened because no contrails (jet engine pollutants) were released and more sunlight reached the earth’s surface.

Global dimming reduces some increase in temperature on earth due to global warming but it is minimal. To go lax on either of the phenomena, thinking that they would cancel each other out, is suicidal. Rise in temperature by 2.5° C is enough to raise sea levels by 6-7 metres by melting polar ice caps, which may flood densely populated areas and destroy the sources of fresh water. Reduction in the intensity of sunlight will disrupt the process of evaporation and precipitation, which might change rainfall patterns. If immediate measures are not taken to stop these manmade effects, then man may himself fall victim to this through climate change.

(Author is pursuing Engineering studies in a leading Bhubaneswar based college)

 

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