Black carbon aerosols arise due to an incomplete combustion of fossil fuels and biomass, and are characterized by their strong capacity for light absorption. Moreover, this carbon’s deposition in snow and ice reduces the albedo of frozen surfaces, which can accelerate the melting of glaciers and snow cover, thus changing the hydrological processes and water resources in these regions. The South Asia areas close to the Tibetan Plateau have among the highest levels of black carbon emissions on our planet, with many scientists warning that black carbon aerosols from South Asia can be transported across the Himalayan Mountains to inland regions of the Plateau.
Now, by analyzing the influence of black carbon aerosols on regional precipitation and glaciers over the Qinghai-Tibet Plateau, an international team of scientists has found that, since the 21st century, these aerosols have indirectly affected the mass gain of the Tibetan Plateau, by changing long-range water vapor transport from the South Asian monsoon region.
“Black carbon aerosols in South Asia heat up the middle and upper atmosphere, thus increasing the North–South temperature gradient,” explained study corresponding author Shichang Kang, an expert in Environmental Studies at the Chinese Academy of Sciences. “Accordingly, the convective activity in South Asia is enhanced, which causes convergence of water vapor in South Asia. Meanwhile, black carbon also increases the number of cloud condensation nuclei in the atmosphere.”
Such changes in the meteorological conditions caused by black carbon aerosols make more water vapor form precipitation in South Asia, weakening the northward transport to the Tibetan Plateau. As a result, precipitation in the southern and central parts of the plateau decreases during the monsoon, leading to a slower rate of mass gain of glaciers. According to the scientists, from 2007 to 2016, this reduced mass gain accounted for 11 percent of the average glacial mass loss on the Tibetan Plateau and 22.1 percent in the Himalayas.
“The transboundary transport and deposition of black carbon aerosols from South Asia accelerate glacier ablation over the Tibetan Plateau. Meanwhile, the reduction of summer precipitation over the Tibetan Plateau will reduce the mass gain of plateau glaciers, which will increase the amount of glacier mass deficit,” Kang concluded.
The study is published in the journal Nature Communications.
By Andrei Ionescu, Earth.com Staff Writer
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