SunCorp

India may be enjoying an unprecedented economic boom, but the country is also facing a darkening environmental scenario.
    A just-published research paper has warned that a blanket of smog hanging over the subcontinent is cutting down sunlight. In fact, the study, by Padma Kumari and her team of scientists at the Indian Institute of Tropical Meteorology in Pune, says India is getting about 5% less sunlight than it did 20 years ago.
    Published in the Geophysical Research Letters and reported in the New Scientist this week, the study found that the amount of solar radiation reaching India’s land mass dropped on an average by 0.86 watts per square metre each year. The decrease was greater during the ’90s than in the ’80s, 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% drop in sunshine over the two decades.
    According to Kumari, smog from industrialization, vehicular pollution, biomass burning, dust storms and the like, 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 reduced sunshine.
    “And because India is on a steep industrialization and development curve, the AOD is only increasing, and sunshine lessening,’’ she told TOI from her office in Pune. How bad it would get depended on a variety of factors, she added, pointing also to a reverse trend in the West.
    “The phenomenon occurs more due to increased aerosol loading in the atmosphere which is the integrated effects of urbanization, industrialization, greater use of vehicles, biomass burning and some other natural causes,’’ she said.
    Ironically, this phenomenon, known as “solar dimming’’, may also be protecting India against global warming. Kumari and her colleagues believe that India is escaping the worst of the warming by greenhouse gas emissions because of smog.
PLUS MINUS
India is getting 5% less sunlight than it did 20 years ago because of a blanket of smog, says a new study
This is because of the integrated effects of industrialization, urbanization and greater use of vehicles
Ironically, the ‘solar dimming’ may be protecting the country from global warming by greenhouse gas emissions
Maximum temperatures during the day have risen by just 0.040°Celsius because of the smog shield. Minimum nighttime temperatures have risen by a much greater 0.310°C Smog shields against global warming
Washington: A study by a team of scientists at the Indian Institute of Tropical Meteorology in Pune has revealed that smog has resulted in India getting lesser sunlight than it did 20 years ago. Ironically, this phenomenon—solar dimming—may also be protecting India against global warming.
    Padma Kumari, who led the team, and her colleagues believe India is also escaping the worst of the warming by greenhouse gas emissions because of smog. Looking at temperature records since the ‘80s, they found maximum and minimum temperatures have both increased, but to different extents.
    Maximum temperatures, which occur during the day, driven by sunshine, have risen by just 0.040°C because of smog’s protective effect. Meanwhile, minimum night-time temperatures, independent of sunshine, have risen by a much greater 0.310°C. However, if the West’s experience and the correctives it applied are 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 until about 1980 had resulted in similar dimming across the world, according to a separate paper by Martin Wild cited by Kumari. But when the West cleaned up its act in the ’80s and ’90s—just as India and China were starting to spew—clearer skies returned. Researchers have described this as “global brightening’’. The downside is that this was accompanied by an accelerated rise in global temperatures.
    Incidentally, Kumari and the team also found that solar dimming over India reduced during the monsoon—because rains brought the fine particles back to earth, allowing more sunshine—giving a new twist to the expression through rain and shine.