Giant Asian Smog Cloud Masks Global Warming Impact -
UN
CHINA: November 14, 2008
BEIJING - A three-kilometre thick cloud of brown soot and other pollutants
hanging over Asia is darkening cities, killing thousands and damaging crops
but may be holding off the worst effects of global warming, the UN said on
Thursday.
The vast plume of contamination from factories, fires, cars and
deforestation contains some particles that reflect sunlight away from the
earth, cutting its ability to heat the earth.
"One of the impacts of this atmospheric brown cloud has been to mask the
true nature of global warming on our planet," United Nations Environment
Programme head Achim Steiner said at the launch in Beijing of a new report
on the phenomenon.
The amount of sunlight reaching earth through the murk has fallen by up to a
quarter in the worst-affected areas and if the brown cloud disperses, global
temperatures could rise by up to 2 degrees Celsius.
But the overall effect of slowing climate change is not the silver lining to
a dark cloud that it appears to be.
The choking soup of pollutants may hold temperatures down overall, but the
mix of particles means it is also speeding up warming in some of the most
vulnerable areas and exacerbating the most devastating impacts of higher
temperatures.
The complex impact of the cloud, which tends to cool areas near the surface
of the earth and warm the air higher up, is believed to be causing a
shortening of the monsoon season in India while increasing flooding there
and in southern China.
Soot from the cloud is also deposited on glaciers, which are at the centre
of environmentalists' and politicians' concerns because they feed Asia's key
rivers and provide drinking water for billions who live along them.
There the particles capture more solar heat than white, reflective snow and
ice -- speeding up melting of a key resource. At a monitoring station near
Mount Everest, soot has been found at levels which scientists say would be
expected in urban areas.
There is also a high human cost. The report estimates round 340,000 people
are dying prematurely because of damage to their lungs, hearts and risk of
cancer.
DARKER CITIES, SMALLER HARVESTS?
Scientists are still studying the impact on crops, but possible problems
include falling harvests because of less energy for photosynthesis and
higher ozone concentrations.
There may also be damage from acidic and toxic particles in the cloud that
land on plants, and wider changes to weather patterns may dry up or flood
fields.
"The emergence of the atmospheric brown cloud problem is expected to further
aggravate the recent dramatic escalation of food prices and the consequent
challenge for survival among the world's most vulnerable populations," the
report said.
One consolation, however, is that if the world stopped emitting the
particles that form the cloud, it could be expected to vanish in weeks,
unlike many longer-lasting greenhouse gasses.
The ingredients that make up the cloud are little different from the smog
that cloaks many of the world's large cities, particularly in developing
nations.
But scientists have realised this local pollution is a global problem,
because of the way it rises and spreads.
"We used to think of the brown cloud as a regional-scale urban problem, now
we know because of fast transport it travels vertically for three to four
kilometres and spreads," said Professor Veerabhadran Ramanathan, head of the
UN scientific panel which is carrying out the research.
There are similar brown clouds over parts of Europe, North America, Africa
and the Amazon Basin, though research so far has been focused on the Asian
cloud which stretches from the Arabian Peninsula to the Pacific Ocean.
(Editing by Valerie Lee)
Story by Emma Graham-Harrison
REUTERS NEWS SERVICE
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