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A blanket of haze,
about three-kilometre thick, hangs over the Indian Ocean. This is the 'Atmospheric Brown
Cloud' (ABC). Spread over the Indian subcontinent, this dense layer of pollution can
drastically alter the region's monsoon pattern, threaten agriculture and damage human
health, say scientists.
ABC was first discovered in 1999, when a study was conducted to find the effect of
airborne particles on climate. It was the Indian Ocean Experiment (INDOEX). An unusually
high concentration of pollutants had been detected, stretched across 1,600 kilometres (km)
off the coast of the northern Indian Ocean, nearly touching the equator. Scientists
noticed a brown haze that contained a cocktail of aerosols. They called it the 'Asian
Brown Cloud' and warned that it could seriously affect the region's climate (See- Going
after hazes).
Aerosol invasion
Aerosols are particles about a millionth of a centimetre in size, comprising sulphates,
soot, carbon and mineral dust. Overall, humans contribute roughly 10 per cent of airborne
aerosols, through automobiles, industries and biomass burning. But in the Indian Ocean
study, scientists found that over 85 per cent of the aerosol-triggered haze was due to
human activity.
Brown clouds, unlike greenhouse gases, reduce sunlight and lowers the temperature. During
the northeast monsoons, they move thousands of miles to the Indian Ocean and cool it. This
reduces evaporation and therefore, decreases the amount of rainfall.
Scientists fear that this atmospherical change will alter the monsoon cycle. Already, the
monsoon clouds are migrating south of India. It is raining more on the sea than on the
land. On land, the aerosols form tiny mist particles that suck out the water from air. So,
the haze dries out the land and floods coastal areas.
In southeast China, the haze has reduced sunlight by two per cent every 10 years since the
1950s. There have been severe storms and floods in southern China in recent years, coupled
with drought in the north. The new weather pattern is the most significant change recorded
in China's climate in 1,000 years…
Not just Asian!
Some scientists were unhappy about the hue and cry raised over the ABC. It diverted
attention from the developed to the developing countries, they felt. And the blame was
shifted from prime greenhouse emitters like the U.S. to the Asian countries.
Soon after, the ABC was renamed as the 'Atmospheric Brown Cloud'. It was seen as a threat
to global climate since it could travel half the globe in three weeks! It could change
rainfall patterns across the Americas and beyond. Also, similar brown clouds were found
over Europe. Therefore, the ABC was not unique to Asia.
But the ABC can be controlled. Since aerosols have a short life span, their spread can be
checked-by using cleaner fuels that burn efficiently and pollute less…
…What is ABC doing?
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It is reducing the amount of sunlight hitting the
Earth's surface by as much as 10-15%. |
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It is warming lower stratas of the atmosphere. |
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Rainfall is decreasing in northwestern parts of Asia and
increasing along the eastern coast of Asia. |
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The haze may reduce precipitation over northwest India,
Pakistan, Afghanistan, western China, and the western central Asian region by 20-40%. |
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It may reduce winter rice harvests in India by 10%. |
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It intensifies the threat of respiratory diseases. |
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