Black carbon aerosols are produced by the incomplete combustion of fossil fuels and biomass, and are characterized by strong light absorption. Black carbon deposition in snow/ice reduces the albedo of snow/ice surfaces, which may accelerate the melting of glaciers and snow cover, thus changing the hydrological process and water resources in the region.
The South Asia region adjacent to the Tibetan Plateau has among the highest levels of black carbon emission in the world. Many studies have emphasized black carbon aerosols from South Asia can be transported across the Himalayan Mountains to the inland region of the Tibetan Plateau.
Recently, a joint research team led by Prof. KANG Shichang from the Northwest Institute of Eco-Environment and Resources of the Chinese Academy of Sciences (CAS), Prof. CHEN Deliang from the University of Gothenburg, and Prof. Robert Gillies from Utah State University analyzed the influence of black carbon aerosols on regional precipitation and glaciers over the Qinghai-Tibet Plateau.
Their findings were published in Nature Communications on Nov. 30.
The researchers found that since the 21st century, South Asian black carbon aerosols have indirectly affected the mass gain of the Tibetan Plateau glaciers 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," said Prof. KANG. "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."
These changes in meteorological conditions caused by black carbon aerosols make more water vapor form precipitation in South Asia, and the northward transport to the Tibetan Plateau was weakened. As a result, precipitation in the central and the southern Tibetan Plateau decreases during the monsoon, especially in the southern Tibetan Plateau.
The decrease in precipitation further leads to a decrease of mass gain of glaciers. From 2007 to 2016, the reduced mass gain by precipitation decrease accounted for 11.0% of the average glacier mass loss on the Tibetan Plateau and 22.1% 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," said Prof. KANG.
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