MENGKE GLACIER, China — Over the years, Qin Xiang and his fellow scientists at a high and lonely research station in the Qilian Mountains of northwest China have tracked the inexorable effects of rising temperatures on one of China’s most important water sources.

“The thing most sensitive to climate change is a glacier,” said Dr. Qin, 42, as he slowly trod across an icy field of the Mengke Glacier, one of the country’s largest. “In the 1970s, people thought glaciers were permanent. They didn’t think that glaciers would recede. They thought this glacier would endure. But then the climate began changing, and temperatures climbed.”

Beneath Dr. Qin’s feet, the cracking ice signaled the second-by-second shifting of the glacier.

The extreme effects predicted of global climate change are already happening in western China. Glacier retreat here and across the so-called Third Pole, the glaciers of the Himalayas and related mountain ranges, threatens Asia’s water supply. Towns and villages along the arid Hexi Corridor, a passage on the historic Silk Road where camels still roam, have suffered floods and landslides caused by sudden summer rainstorms. Permafrost is disappearing from the Tibet-Qinghai Plateau, jeopardizing the existence of plants and animals, the livelihoods of its people and even the integrity of infrastructure like China’s high-altitude railway to Lhasa, Tibet.

The fact that Chinese scientists are raising alarms about these changes is a key reason that the Chinese government has been engaging fully in climate change negotiations in recent years. Another is the deadly urban air pollution, caused mostly by industrial coal burning, that resulted in Beijing’s first red alert over air quality on Monday.