Heavy pollution dimming skies from Delhi to Beijing

New York, Nov 14 (PTI) Asian cities from New Delhi to Beijing are getting darker, glaciers on the mighty Himalayas are melting faster and weather system is getting more extreme, a United Nations study has warned.

This alarming phenomenon has also spread its dragnet to other cities like Mumbai, Kolkata, Bangkok, Tehran, Cairo, Seoul, Karachi, Dhaka and Shanghai.

What common citizens perceived for long as an early onset of winter, is not so.

The U.N. study now says this is the result of burning of fossil fuels and biomass, the Atmospheric Brown Clouds (A.B.C.s), made of soot and other man-made particles, are more than three km-thick.

The report compiled by the UN Environment Programme (U.N.E.P.) has said that the dimming is as much as between 10-25 percent over cities like New Delhi, Karachi, Beijing and Shanghai.

But the worst hit appears to be the Chinese city of Guangzhou, where sunlight in winter had dimmed by more than 20 percent since the 1970s.

For India as a whole, the dimming trend has been running at about two percent per decade between 1960 and 2000 - more than doubling between 1980 and 2004, it adds.

In China the observed dimming trend from the 1950s to the 1990s was about 3 to 4 percent per decade, with the larger trends after the 1970s, says the report.

It warns that the layer that stretches from the Arabian Peninsula to China and the western Pacific Ocean, are in some cases and regions aggravating the impacts of greenhouse gas-induced climate change, a team of experts drawn from research centres in Asia, including China and India, said.

The study was conducted by the team drawn from research centres in Asia including India and China, Europe and the United States, announced their latest and most detailed assessment of the phenomenon.

The brown clouds, the toxic result of burning of fossil fuels and biomass, are in some cases and regions aggravating the impacts of greenhouse gas-induced climate change, the report stresses.

This is because A.B.C.s lead to the formation of particles like black carbon and soot that absorb sunlight and heat the air; and gases such as ozone enhance the greenhouse effect of carbon dioxide.

Globally however brown clouds may be countering or 'masking' the warming impacts of climate change by between 20 and up to 80 percent, the researchers suggest.

The cloud is also affecting air quality and agriculture in Asia and increasing risks to human health and food production for three billion people.

Achim Steiner, U.N. Under-Secretary General and Executive Director, U.N.E.P., said, "I expect the Atmospheric Brown Cloud to be now firmly on the international community's radar as a result of today's report".

The five regional hotspots for A.B.C.s identified in the
report includes the Indo-Gangetic plains in South Asia from
the northwest and northeast regions of eastern Pakistan across
India to Bangladesh and Myanmar, the U.N.E.P. said in a press
statement.

New Delhi, Kolkata and Mumbai feature in the list of 13
megacities where A.B.C.s are reducing the sunlight hitting the
Earth's surface, making the cities "darker or dimmer".

Professor Veerabhadran Ramanathan, head of the United
Nations Environment's scientific panel which is carrying out
the research, said the report brings ever more clarity to the
A.B.C. phenomena and in doing so must trigger an international
response.

"One of the most serious problems highlighted in the
report is the documented retreat of the Hind
Kush-Himalayan-Tibetan glaciers, which provide the head-waters
for most Asian rivers and thus have serious implications for
the water and food security of Asia," he said.

Scientists said there are also brown clouds elsewhere
including over parts of North America, Europe, southern Africa
and the Amazon Basin.

A.B.C.s, says the report, can reduce sunlight hitting the
Earth's surface in two ways. Some of the particles such as
sulphates, linked with burning coal and other fossil fuels,
reflect and scatter rays back into space.

Others, also linked with fossil fuel and biomass burning,
in particular black carbon in soot, absorb sunlight before it
reaches the ground. The overall effect is to make 'hot spot'
cities darker or dimmer.

The report says particles and aerosols in the A.B.C.s may
act to inhibit the formation of rain drops and rainfall.

"The net effect is an extension of cloud life-times,"
says the report.

A.B.C.s shield the surface from sunlight by reflecting
solar radiation back to space and by absorbing heat in the
atmosphere. These two dimming phenomena can act to
artificially cool the Earth's surface especially during dry
seasons. The pollution can also be transported around the
world via winds in the upper troposphere. PTI