Soot from India a ‘serial killer’ for glaciers in Tibet, scientists say
Soot from India has proven more destructive than global warming in terms of harming glaciers in parts of Tibet, according to a joint study by researchers in China and the United States.
In fact, most of the carbon-containing aerosols in the Himalayan region come from the soot created when coal and biomass is burnt in South Asia, the scientists said.
They based their findings on a core of ice measuring 100 metres in length that Chinese scientists retrieved during an expedition to the Zuoqiupu glacier in southeastern Tibet’s Kangri Karpo mountain range in 2007. They took it to the Tibetan capital of Lhasa for further study.
Bored from an altitude of 5,600 metres above sea level, the ice showed a history of soot deposits dating from 1956 to 2005.
The team described soot as a “serial killer” in terms of how it impacts the slowly moving rivers of ice that coat mountains in areas like Tibet, which straddles the Sino-Indian border.
When airborne, soot increases atmospheric temperatures and reduces snowfall. After it lands on ice or snow, it absorbs heat from the sun, causing glaciers to melt faster.
The fast retreat of glaciers in Tibet has long-puzzled scientists, as they have been melting at twice the estimated rate of the impact of climate change.
Their rapid erosion has also greatly troubled China as its three biggest rivers - the Yangtze, Yellow River, and Lancang River in southern Yunnan province - all originate from the Tibetan Plateau. As such, the glaciers play a critical role in China’s long-term water supply.
Soot was a major suspect as previous studies found traces of black and organic carbon all over the Himalayan region, but scientists were unable to pinpoint whether it came from China or India as both countries consume vast amounts of coal and rank as major emitters of pollutants.
Factories and farms in India are geographically closer to the glaciers, but doubts remained as to whether their emissions would be able to scale Mount Everest and find their way into Tibet.
The new study, which was published in the latest issue of Atmospheric Chemistry and Physics, took various approaches to trace the source of the soot. The team began by analysing its chemical fingerprint.
“The emissions from China and India carry their own district chemical compositions,” said professor Xu Baiqing, one of the authors of the paper. Xu works for the Chinese Academy of Sciences’ Institute of Tibetan Plateau Research in Beijing.
“For instance, the soot from China contained more black carbon from fossil fuels, while the Indian soot had more organic carbon, which resulted from the burning of hay and wood in rural areas,” he said.
India contributed 74 per cent of the black carbon and 81 per cent of the organic carbon in the core of ice, according to their analysis.
They also found that the size of the soot deposits on the Zuoqiupu glacier had grown significantly over the years. From the 1980s onwards, the fallout was three times higher than in previous decades, with the rate of heat absorption also up threefold.
The soot deposits found in the glacier were attracting enough heat from the sun to power an LED bulb, the scientists said.
To verify whether the soot was coming from India, the researchers used a new modeling technique developed by scientists at the Pacific Northwest National Laboratory in the US. The two teams collaborated on the project to find out how the soot was able to travel across the mountains between the two countries.
The model was able to track emissions from different regions and regenerate the flow of soot in the atmosphere as it was tossed about by monsoons and other climatic events.
They found that soot levels in the Zuoqiupu glacier rose and fell over the years in proportion to the amount of coal consumed in India. They also spiked and dipped in line with the country’s hay-burning seasons.
It took tremendous effort to remove the large core of ice, occasionally under life-threatening conditions, said Xu, who participated in the expedition.
To ensure it was free of contamination by the activities of local people, the Chinese scientists picked one of the most remote areas in Southern Tibet, far from any human settlement.
Scientists warned that the threat to the glaciers needs to be addressed urgently as large populations rely on drinking water sourced there.
“If the Indian government can do something about it, such as reducing its burning of hay and firewood in rural areas, we will see a quick improvement,” Xu said.
“Soot doesn’t stay in the air for long. As soon as the emissions are cut, the fallout will drop.”