Perilous
Times and Climate Change
Asia's air pollution brewing monster killer storms,
scientists say
* From: AFP
* November 03, 2011 10:57AM
Air pollution from South Asia is helping to brew monster storms in
the Arabian Sea that have claimed thousands of lives and cost
billions of dollars, scientists say. Source: The Daily Telegraph
AIRBORNE pollution from South Asia is helping to brew monster
storms in the Arabian Sea that have claimed thousands of lives and
cost billions of dollars, scientists said yesterday.
In a paper published in the British journal Nature, researchers
pointed the finger at a haze known as the Asian brown cloud, which
hangs over parts of the northern Indian Ocean, India and Pakistan.
Several kilometres thick, the cloud comprises brownish particles
of carbon soot and sulphates spewed by factories, diesel exhaust
and poorly-burnt biomass.
Previous research has implicated it in disrupting monsoon patterns
and in glacier loss in the Himalayas.
Environmental scientists led by Amato Evan of the University of
Virginia looked at patterns in cyclones in the Arabian Sea from
1979 to 2010.
They found the region historically only averaged two or three
cyclones a year and these typically were weak -- even though the
sea was clearly hot enough to fuel very powerful storms.
The reason for the weakness and infrequency, they discovered, lies
in a phenomenon called vertical wind shear which occurs in July
and August during the hot months of the monsoon season.
Vertical wind shear occurs when strong winds flow in the upper and
lower atmosphere in opposite directions. In the lower levels, it
blows from the southwest, and in the upper atmosphere, from the
east.
The shear rips the top off a would-be cyclone, preventing it from
developing the circular winds that are its muscular hallmark.
As a result, the few cyclones that occurred in the Arabian Sea
typically happened before or after the monsoon season - usually
one in May/June and a couple more in August to December - when the
wind shear was far less.
But in the last dozen or so years, the pattern has changed, with
the emergence of storms in the weeks immediately before the
monsoon season.
They include a cyclone that killed nearly 3,000 people in Gujarat,
India, in June 1998.
In June 2007, cyclone Gonu, a category five storm, killed 49
people in Oman and Iran, causing more than four billion dollars in
damage. It was the first documented storm ever to enter the Gulf
of Oman.
And in June 2010, 26 people were killed in Pakistan and Oman by a
category-four cyclone, Phet, inflicting losses of nearly two
billion dollars.
The team says "brown cloud" particulates have grown six-fold in
volume since the 1930s and the pollution is now a disruptive
climatic phenomenon in its own right.
Its dark colour absorbs sunlight, making it a source of heat and
causing a cooling of the ocean below -- which in turn affects wind
circulation and the transport of warmth from the sea to the
atmosphere.
Drawn from direct observations and computer models, the conclusion
is that the cloud weakens wind shear, essentially lifting the
brake on cyclone development.
"This study is a striking example of how human reactions, on a
large enough scale -- in this case, massive regional air pollution
caused by inefficient fuel combustion -- can result in unintended
consequences," said Anjuli Bamzai of the US National Science
Foundation.
"These consequences include highly destructive summer cyclones
that were rare or non-existent in this monsoon region 30 or so
years ago."
Arabian Sea cyclones could be particularly hazardous because they
are born in a small area of ocean compared to the tropical western
Atlantic and the western Pacific, the study warned.
"Given the relatively small size of the Arabian basin, more than
half of all cyclones that form here make landfall, and even weak
landfalling Arabian Sea cyclones can cause considerable
destruction and loss of life."
AFP