Pollution Clouds Multiplying Heat by 50 Percent

Pollution Clouds Multiplying Heat by 50 Percent



Aug. 2007  - Brown clouds of pollution 
over South Asia have multiplied solar heating of the lower atmosphere by 
50 percent, finds new research by scientists at Scripps Institution of 
Oceanography at the University of California-San Diego.


The combined heating effect of greenhouse gases and the brown clouds is 
necessary and sufficient to account for the retreat of Himalayan glaciers 
observed over the past 50 years, the researchers conclude. 
Led by Scripps atmospheric chemistry professor Veerabhadran Ramanathan, 
the team describes their findings in a paper to be published in the August 
2 edition of the journal "Nature." 
Not entirely made up of water vapor like regular clouds, brown clouds 
contain soot, sulfates, nitrates, hundreds of organic compounds, and fly 
ash from urban, industrial and agricultural sources. 
"The conventional thinking is that brown clouds have masked as much as 50 
percent of the global warming by greenhouse gases through the so-called 
global dimming," said Dr. Ramanathan. 
"While this is true globally," he said, "this study reveals that over 
southern and eastern Asia, the soot particles in the brown clouds are 
intensifying the atmospheric warming trend caused by greenhouse gases by 
as much as 50 percent." 

 
The Himalayan glaciers feed the major Asian rivers - the Yangtze, the 
Ganges and the Indus - that supply water to billions of people in China, 
India and across southeast Asia. 
"The rapid melting of these glaciers, the third-largest ice mass on the 
planet, if it becomes widespread and continues for several more decades, 
will have unprecedented downstream effects on southern and eastern Asia," 
the authors warn. 
"Ramanathan and colleagues, for the first time ever, used small and 
inexpensive unmanned aircraft and their miniaturized instruments as a 
creative means of simultaneously sampling of clouds, aerosols and 
radiative fluxes in polluted environments, from within and from all sides 
of the clouds," said Jay Fein, program director in the National Science 
Foundation's Division of Atmospheric Sciences.
The aircraft, flying in stacked formations over the Maldives, an island 
nation in the Indian Ocean, measured the brown clouds from different 
altitudes, creating a profile of soot concentrations and light absorption 
unprecedented in its level of vertical detail. 
The flights took place in March 2006 during the region's dry season when 
air masses, loaded with industrial and vehicle emissions and pollution 
from biomass burning, travel south from the continent to the Indian Ocean. 


 
"These measurements, combined with routine environmental observations and 
a state-of-the science model, led to these remarkable results," said Fein. 

When the researchers fed both greenhouse gas and brown cloud data into 
computer climate models, they found that the region's atmosphere has 
warmed 0.25 degrees Celsius (0.5 degrees F) per decade since 1950 at 
altitudes ranging from two to five kilometers (6,500 to 16,500 feet) above 
sea level - the same altitude where the Himalayan glaciers lie. 
The analysis showed that the brown cloud effect is necessary to explain 
temperature changes that have been observed in the region over the last 50 
years. 
It also indicates that south Asia's warming trend is more pronounced at 
higher altitudes than closer to sea level. 
Achim Steiner, executive director of the UN Environment Programme which 
helped support the research, said, "The main cause of climate change is 
the buildup of greenhouse gases from the burning of fossil fuels. But 
brown clouds, whose environmental and economic impacts are beginning to be 
unraveled by scientists, are complicating and in some cases aggravating 
their effects." 
Steiner hopes the Scripps' research will spur the international community 
to take urgent action to limit global warming, in particular at the next 
crucial UN climate change convention in Indonesia this December. This 
conference is expected to negotiate a global successor agreement to the 
Kyoto Protocol, which expires in 2012. 
By burning less fossil fuels, South Asia may be able to arrest the 
glaciers' retreat and reduce regional air pollution at the same time. 
Steiner said, "It is likely that in curbing greenhouse gases we can tackle 
the twin challenges of climate change and brown clouds and in doing so, 
reap wider benefits from reduced air pollution to improved agricultural 
yields." 

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