Pollutants from China and India, are not only increasing in quantity but are also being pumped to greater heights in the atmosphere, and may be affecting the very pattern of the South Asian monsoon, scientists have discovered.
A new paper published in the journal Climate Dynamics in November concludes that aerosols have strong impacts on regional monsoon rainfall and circulation. In turn, this pollution is affecting the very pattern of the South Asian monsoon. The polluting aerosols, from the burning of fossil fuels and, to a lesser extent, biomass, also absorb heat from the sun’s radiation, further increasing global warming.
The scientists found that the complex and steep topography of the Himalayan foothills help in the build-up of thick layers of dust aerosols transported by monsoon winds from the Arabian deserts across the Arabian Sea. This build-up of aerosols causes the monsoon to arrive early. These findings are important not only for climate change but also for predicting the Asian monsoon in the future.
A team of scientists headed by William Lau from the Earth Science Interdisciplinary Center, University of Maryland, studied the unusual 2008 Indian monsoon. This year saw “exceptional heavy loading of dust aerosols over the Arabian Sea and northern-central India, near normal all-India rainfall, but excessive heavy rains and disastrous floods in the Northern Indian Himalaya Foothills, and persistent drought conditions in central and southern India,” according to the paper.
The idea that hot air and pollution is pumped up over the Himalayas was first put forward in 2006 by a team also led by Lau. Lau proposed that in the pre-monsoon season, from March to May, soot from northern India and dust from the deserts of western China, Afghanistan and Pakistan gather at the foothills of the Himalayas in the Indo–Gangetic Basin. Since these aerosols absorb heat, they warm the surrounding air, making it rise vertically over the Himalayas to more than 10-15 km high, acting like an “elevated heat pump”. The rising warm air, in turn, sucks in cooler air from the Indian Ocean, causing an earlier onset of the monsoon.
