Though I lived in China’s Xinjiang Uyghur Autonomous Region for almost two years, it was only when I was in the heart of the Tian Shan mountains, my motorcycle meandering its way around fallen rock, sheep herds and horses, that I felt truly at home. Just a few hours outside of the city of Shihezi, inspiring peaks soared over 4000 meters. Though I had no scientific data to support my feeling that these stunning vistas were impermanent, over the course of my stay there were fewer and fewer clear days to see the cresting glacier-capped peaks from my apartment window. The haze even began to influence my weekend trips deep into the mountains, sometimes choking off the views far outside of the city. There is too much pollution in these mountains, not like when I was a child— a common refrain that echoed among many Kazakh and Mongol herders who made their home there.
In a recent article in the journal of Arctic, Antarctic, and Alpine Research, Baojuan Huai and a team of Chinese researchers use remote sensing to put scientific data in the place of the herders’ and my own perceptions. The glaciers of the Tian Shan— the impressive mountain range that historically has divided the region’s agrarian oasis-states to the south and nomadic communities to the north— are in danger of disappearing. The authors demonstrate that in the Chinese Tian Shan, the total area of the glaciers studied has decreased by 22 percent over a fifty year period. The data also shows that glacier retreat is a variable within different regions of the Tian Shan— the result of a convergence of factors both human-caused and natural.
China is home to a baffling 46,377 glaciers. The Xinjiang Uyghur Autonomous Region contains 18,311 of them. The Tian Shan, which cuts across Xinjiang into Kazakhstan and Kyrgyzstan, boasts the largest number of glaciers in northwest China. These glaciers provide invaluable solid reservoirs to agriculture, animal husbandry, and industry in the region. When considering the Tian Shan range alone, the glacial loss will continue to have a severe impact on the livelihoods and ecology of Xinjiang, according to Weijun Sun, one of the paper’s authors. “Warming temperatures are causing a real reduction to glaciers across China, and ablation is occurring constantly, negatively impacting regional ecology,” he said in an interview with GlacierHub.
To acquire data for so many glaciers, the team utilized remote sensing technology, which relies on satellites to monitor different sites, using automated glacier mapping technology to distinguish glaciers from other features. Remote sensing alleviates many of the difficulties typically faced in conducting research on glaciers, which are often remote and difficult to access, according to Sun. “Remote sensing is a fantastic tool, expanding the scope of what we are capable of measuring. With this technology we can now measure things like the amount of reflectance coming from under the surface, or the temperature at the base,” he stated.
For the study, the team selected glaciers that covered a range of variables: glaciers large and small, debris-covered and debris-free, and at high and low elevations were all represented. The research shows that over the period studied, 182 Tian Shan glaciers disappeared, and several large glaciers divided into multiple small glaciers. The percentage of area reduction tended to be higher in small glaciers than in large glaciers, with small glaciers more likely to shrink significantly or disappear entirely.
Glaciers across the Tian Shan experienced a real loss over the period studied, but the rate of change between regions within the mountain range showed significant variability. While glacier loss in one region was as low as 12 percent, total glacier area loss reached 42 percent in another. This variability is caused by a constellation of factors, according to Sun. “Regional variation is primarily caused by differing historical climatic factors, such as temperature, precipitation, and radiation,” he said.
Over the period under consideration, the annual temperature increase in Xinjiang was 0.29 degree Celsius per decade, almost double the global average. Additionally, annual precipitation increased at a rate of 10.6mm per decade, which increased the sensitivity of glaciers at lower elevations to rising temperatures. However, the extent of these increases were not constant throughout the region.
When considering the causes of intensified areal loss in certain parts of the Tian Shan, looking at the specific topography of individual glaciers is critical, according to Tobias Bolch, a glaciologist at the University of Zurich. “The glaciers in Central Tian Shan receive more accumulation during the summer while glaciers in the outer rages receive more accumulation during winter. These summer-accumulation type glaciers are more sensitive to climate change. In addition, the Central Tian Shan is higher than the outer ranges; hence, the glaciers in the Central Tian Shan can have larger accumulation areas,” he stated in an interview with GlacierHub.
In the decades considered in the study, the mean equilibrium line altitude (ELA)— the point on the glacier at which annual ablation and accumulation are equal— increased in altitude. The increases ranged from only 5 meters for one glacier, to as many as 151 meters in another. The increases in mean glacier elevation indicate that glaciers are unable to survive at the lower elevations they once thrived in. Glaciers have been retreating before the eyes of pastoralists for decades; that Chinese researchers have put data in the place of their inaudible perceptions is cause for celebration, if not another motorcycle trip.