How Now Brown Cloud

“Atmospheric brown clouds” stretch from Dubai to Shanghai; they reduce crop yields by blocking sunlight,and contribute to extreme weather that also hurts agriculture. The polluted clouds come from burning fossil fuels. USA Today says, “The huge plumes have darkened 13 megacities in Asia — including Beijing, Shanghai, Bangkok, Cairo, Mumbai and New Delhi — sharply “dimming” the amount of light by as much as 25% in some places.”

Among the effects of this phenomenon is a decrease in the monsoon rains over India in recent years, with potentially disastrous effects on the agriculture that sustains over a billion people.

They are hastening the melting of the glaciers in northern Pakistan and India, with perhaps deadly implications for the rivers that flow from those headwaters. Pakistan without the “five rivers” and the Indus would be a wasteland.

And then they say that petroleum is “cheaper” than solar energy! Is anyone figuring in the cost of the atmospheric brown clouds? How many billions of dollars are they costing in higher food prices and extreme climate events?

The report is here in pdf format.

The UN Environmental Program executive summary contains the following passages:

“Beijing/Nairobi, 13 November 2008 – Cities from Beijing to New Delhi are getting darker, glaciers in ranges like the Himalayas are melting faster and weather systems becoming more extreme, in part, due to the combined effects of man-made Atmospheric Brown Clouds (ABCs) and greenhouse gases in the atmosphere.

These are among the conclusions of scientists studying a more than three km-thick layer of soot and other manmade particles that stretches from the Arabian Peninsula to China and the western Pacific Ocean.

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

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

This is because ABCs lead to the formation of particles like black carbon and soot that absorb sunlight and heat the air; and gases such as ozone which enhance the greenhouse effect of CO2.

Globally however brown clouds may be countering or ‘masking’ the warming impacts of climate change by between 20 and up to 80 per cent the researchers suggest.

This is because of particles such as sulfates and some organics which reflect sunlight and cool the surface.

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

“In doing so, they can not only lift the threat of climate change but also turn off the soot- stream that is feeding the formation of atmospheric brown clouds in many of the world’s regions. This is because the source of greenhouse gases and soot are often one and the same – unsustainable burning of fossil fuels, inefficient combustion of biomass and deforestation,” he added. . .

“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.

“The new research, by identifying some of the causal factors, offers hope for taking actions to slow down this disturbing phenomenon; it should be cautioned that significant uncertainty remains in our understanding of the complexity of the regional effects of ABCs and more surprises may await us ” added Professor Ramanathan.

Highlights from Atmospheric Brown Clouds: Regional Assessment Report with Focus on Asia

Five regional hotspots for ABCs have been indentified. These are:

* East Asia, covering eastern China;

* The Indo-Gangetic plains in South Asia from the northwest and northeast regions of eastern Pakistan across India to Bangladesh and Myanmar;

* Southeast Asia, covering Cambodia, Indonesia, Thailand, and Vietnam;

* Southern Africa extending southwards from sub-Saharan Africa into Angola, Zambia and Zimbabwe; and

* The Amazon Basin in South America.

There are hotspots too in North America over the eastern seaboard and in Europe – but winter precipitation tends to remove them and reduce their impact.

Cities and ‘Dimming’

Around 13 megacities have so far been identified as ABC hotpots.

Bangkok, Beijing, Cairo, Dhaka, Karachi, Kolkata, Lagos, Mumbai, New Delhi, Seoul, Shanghai, Shenzhen and Tehran where soot levels are 10 per cent of the total mass of all human-made particles.

ABCs 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.

* ‘Dimming’ of between 10-25 per cent is occurring over cities such as Karachi, Beijing, Shanghai and New Delhi

* Guangzhou is among several cities that have recorded a more than 20 per cent reduction in sunlight since the 1970s

* For India as a whole, the dimming trend has been running at about two per cent per decade between 1960 and 2000 – more than doubling between 1980 and 2004.

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

Impact on Cloud Formation and a Further Dimming Effect

* Regions with large concentrations of ABCs may be getting cloudier which can also contribute to dimming but data are not sufficient to quantify this effect.

* Particles and aerosols in the ABCs may act to inhibit the formation of rain drops and rainfall. “The net effect is an extension of cloud life-times,” says the report.

Masking the Impacts of Climate Change

ABCs 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 (above 5 km in altitude).

* As a result global temperature rises – linked with greenhouse gas emissions – may currently be between 20 per cent and 80 per cent less as a result of brown clouds around the world says the report.

* If brown clouds were eliminated overnight, this could trigger a rapid global temperature rise of as much as to 2 degrees C.

* Added to the 0.75 degrees C rise of the 20th century, this could push global temperatures well above 2 degrees C – considered by many scientists to be a crucial and dangerous threshold. . . .

Simply tackling the pollution linked with brown cloud formation without simultaneously delivering big cuts in greenhouse gases could have a potentially disastrous effect. . .

The science secretariat of ABC is located at the Center for Clouds, Chemistry and Climate, Scripps Institution of Oceanography, UCSD.

The current project is funded by UNEP with support from the governments of Italy, Sweden and the United States.

Atmospheric Brown Clouds: Regional Assessment Report with Focus on Asia can be found at .”

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