3km-thick brown cloud over Asia
2008-11-14 08:07
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.
'Silver lining' not that bright
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 ° 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.
Speeding up meltdown
Soot from the cloud is also deposited on glaciers, which
are at the centre of environmentalists' and politicians'
concerns because the glaciers feed Asia's key rivers and provide drinking water for billions.
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.
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.
Worldwide problem
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.