Researchers have found that aerosols are efficiently cutting down the amount of solar energy reaching the Earth’s surface, thereby cooling the surface, while warming the atmosphere significantly across the Indo-Gangetic Plains (IGP) and the Himalayan foothills. This confirms that aerosols are a major driver of climate change in the region and these would accelerate glacier retreat and snow melt.
A regional and seasonal analysis of aerosol observations was carried out for the first time at ten locations in India, Nepal, Bangladesh and Pakistan. These included New Delhi, Karachi and Lahore and in western IGP, Kanpur, Gandhi College and Lumbini in central IGP, Dhaka and Bhola in eastern IGP, and Pokhara and Kathmandu in the Himalayan foothills.
The study revealed that chemical characteristics of aerosols, aerosol radiative effects and aerosol-induced atmospheric heating rate vary both qualitatively and quantitatively across the IGP and the Himalayas. Aerosol optical depth values over all the locations during the year confirmed that the entire region is heavily polluted and exhibits significant spectral and seasonal variations.
“In the present day scenario, the regionally-coherent large aerosol-induced atmospheric heating rates could be critical to the total atmospheric warming (greenhouse plus aerosols) in the region,” the researchers said while observing that the heating rate at all sites throughout the year over the IGP and the Himalayas indicated that warming due to aerosols is quite coherent over a large region in northern South Asia.
The study, undertaken by researchers from the Department of Space’s Physical Research Laboratory, Ahmedabad and the GFZ Helmholtz Centre for Geosciences, Germany, has been published in the current issue of Atmospheric Environment, an international peer reviewed journal.
The IGP, which includes parts of India, Nepal, Pakistan and Bangladesh, is a highly polluted, densely populated, intensely cultivated and industrialised region, with diverse aerosol emissions from natural and anthropogenic sources giving rise to a persistent blanket of haze, the researchers observed.
The Himalayas and the surrounding regions have globally important yet fragile ecosystems and highly vulnerable population, and still remain one of the less studied regions in terms of aerosols. The aerosol properties and trace gases over the Himalayan foothills and the Himalayas are largely affected by biomass burning emissions, forest fires, burning of crop waste and bio-fuels used in cooking and heating.
In addition, atmospheric dynamics plays a dominant role in transporting and transforming the aerosols over this region. Air pollution over the Himalayas and the surrounding regions affects the health of large populace of people and ecosystems, crops, climate, cryosphere, precipitation and monsoon, according to the researchers.
“Our results reveal that as the elevation increases in the Himalayan foothills, the aerosol-induced atmospheric solar heating rates and likely the local warming increase. Such significantly high heating rates over the Himalayas have significant climate implications,” the researchers said.
“The glaciers in the Hindu Kush-Himalayan-Tibetan Plateau region that tend to the Yangtze, the Indus and the Ganges, the major rivers in Asia, have witnessed a notable retreat. The atmospheric warming by black carbon is expected to accelerate glacier and snow melt,” they cautioned.
