PUNE: Air pollution and a rise in west Pacific tropical cyclones have played their parts in weakening the Indian monsoon the past few decades, according to a study by researchers from Indian Institute of Tropical Meteorology in Pune.
The researchers held that greenhouse gas emissions and other human activities can significantly alter the pattern of monsoon flow over the tropical Indo-Pacific Oceans and lead to an increase in tropical cyclones over the west Pacific. Higher frequency of tropical Pacific cyclones can cause a weakening of the monsoon, as it is associated with moisture depletion over India. “Monsoon in India depends on low-level moisture transport from the Indian Ocean towards the Indian landmass. This flow tends to weaken due to human-induced pollution as per our model simulations,” said Dr TP Sabin, a senior IITM scientist. The study was led by Dr R Krishnan, director of the institute.
“Human-induced climate drivers, particularly greenhouse gases and aerosols, can impact precipitation patterns over the Asian monsoon region. While the increase in greenhouse gases can intensify rainfall, aerosol emissions (minute suspended pollutant particles) exert the opposite influence,” Sabin said. The scientist explained that high levels of aerosol in the atmosphere can deflect the sun’s heat back into space rather than warming the earth’s surface. “This leads to a decrease in temperatures on the earth’s surface and reduces rainfall,” he said. The study found that aerosol emissions in the northern hemisphere have contributed to a decline in monsoon rainover India.