Global Warming: India Getting Less and Less Sunlight

by Gopalan on Nov 16 2007 11:20 AM

Global Warming: India Getting Less and Less Sunlight
India is getting darker, this time literally. Yes, a just-published research paper has warned that a blanket of smog hanging over the subcontinent is cutting down sunlight.
A study by Padma Kumari and her team at the Indian Institute of Tropical Meteorology in Pune says India is getting about 5 per cent less sunlight than it did 20 years ago.

The study, published in the Geophysical Research Letters and reported in the New Scientist this week, found that the amount of solar radiation reaching India’s land mass dropped on average by 0.86 watts per square meter each year. The decrease was greater during the 1990s than the 1980s, suggesting that increased industrial activity was accelerating the trend.

Padma Kumari and team studied data from the India Meteorological Department, measuring differences in solar radiation at 12 stations across India between 1981 and 2004. They determined that the average decline corresponded to a 5 per cent drop in sunshine over the two decades.

According to Kumari, smog resulting from industrial activity, vehicular pollution, biomass burning, dust storms etc is increasing Aerosol Optical Depth (AOD). Greater AOD, which is the optical depth due to extinction by the aerosol component of the atmosphere, results in lesser sunshine.

”And because India is on a steep industrialization and developmental curve, the AOD is only increasing, ands sunshine lessening” she said in an interview to Times of India.. How bad it would get depended on a variety of factors, she added, pointing also to a reverse trend in the West.

Ironically, this phenomenon, known as “solar dimming” may also be protecting India against global warming.

Kumari and colleagues believe that India is also escaping the worst of the warming by greenhouse gas emissions because of smog. Looking at temperature records since the 1980s, they found that maximum and minimum temperatures have both increased, but to different extents.

Maximum temperatures, which occur during the day and are driven by sunshine, have risen by just 0.04°C because of the protective effect of smog. Meanwhile, minimum, night-time temperatures, which are independent of sunshine, have risen by a much greater 0.31°C.

However, if the experience of the West and the correctives it applied is any indication, there is light at the end of the tunnel, and brighter days may be ahead, although it might not be anytime soon.

It turns out that smog produced by the US and Europe up until about 1980 had resulted in similar dimming across the world, according to a separate paper by Martin Wild that Kumari cited. But when the west cleaned up its act in the 1980s and 1990s—just as India and China were starting to spew—clearer skies returned across much of the world. Researchers have described this as “global brightening.”

The downside: this global brightening was accompanied by an accelerated rise in global temperatures.

Incidentally, Kumari and team also found that solar dimming over India was lessened during the monsoon season—because the torrential rains brought the fine particles back down to Earth, allowing more sunshine to get through—giving a new twist to the expression through rain and shine.

The Intergovernmental Panel on Climate Change (IPCC) had warned in April last that global warming could cause more hunger in poor countries and melt most Himalayan glaciers by the 2030.

The agency also said that up to 40 animal and plant species faced extinction as rising temperatures destroy the ecosystems that support them.

The IPCC, joint Nobel Peace Prize winner this year, had observed, that animal and plant life in the Arctic and Antarctic was undergoing substantial change and that rising sea levels elsewhere are damaging coastal wetlands.

Warmer waters were bleaching and killing coral reefs, pushing marine species toward the poles, reducing fish populations in African lakes, it said.

”Hundreds of species have already changed their ranges, and ecosystems are being disrupted,” said University of Michigan ecologist Rosina Bierbaum, former head of the US IPCC delegation. “It is clear that a number of species are going to be lost.”


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