Brown clouds of pollution over South Asia have multiplied solar heating of the lower atmosphere by 50 percent, says a new research by scientists at the Scripps Institution of Oceanography at the University of California, San Diego.
Sources said here on Thursday that the combined heating effect of greenhouse gases and the brown clouds was necessary and sufficient to account for retreating Himalayan glaciers observed over the past 50 years.
The research says that not only entirely made up of water vapour like regular clouds, the brown clouds also contain soot, sulphates, nitrates, hundreds of organic compounds and fly ash from urban, industrial and agricultural sources. The conventional thinking is that these brown clouds have masked as much as 50 percent of the global warming by greenhouse gases through the so-called global dimming. While this is true globally, 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 research says 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, Pakistan and across south-east 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 of the research warn.
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 kilometres (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.