SPEAKING this week at the United Nations, President Hu Jintao of China declared that his country “fully appreciates the importance and urgency of addressing climate change." As well it should. China is beginning to realize that it has a lot to lose from the carbon dioxide that the world so blithely emits into the earth's atmosphere. Mr. Hu's words made me think back to a day not long ago when I found myself on a platform 14,000 feet above sea level, surrounded by throngs of Chinese tourists in colorful parkas. A chairlift had brought us that much closer to the jagged peaks of Jade Dragon Snow Mountain and the glacier that cascades down its flank. People cheerfully snapped photos of the icy mass, seemingly unaware of the disaster unfolding before them. Because of climate change, the roughly 1.7-mile-long Baishui Glacier No. 1 could well be one of the first major glacial systems on the Tibetan Plateau to disappear after thousands of years. The glacier, situated above the honky-tonk town of Lijiang in southwest China, has receded 830 feet over the last two decades and appears to be wasting away at an ever more rapid rate each year. It is the southernmost glacier on the plateau, so its decline is an early warning of what may ultimately befall the approximately 18,000 higher-altitude glaciers in the Greater Himalayas as the planet continues to warm. Because the Tibetan Plateau and its environs shelter the largest perennial ice mass on the planet after the Arctic and Antarctica, it has come to be known as “the Third Pole.” Its snowfields and glaciers feed almost every major river system of Asia during hot, dry seasons when the monsoons cease, and their melt waters supply rivers from the Indus in the west to the Yellow in the east, with the Ganges, Brahmaputra, Irrawaddy, Salween, Mekong and Yangtze Rivers in between. (The glaciers on Jade Dragon Snow Mountain contribute much of their water to the upper reaches of the Yangtze River.) From a distance, Baishui Glacier No. 1 looks as immovable as the defiant mountain above. In reality, it is a fluid field of ice and rock in constant downward motion. Scientists speak about the reactive behavior of these glaciers as if they were almost human. The Tibetan and Naxi peoples who inhabit this region treat them, and their mountain hosts, as embodiments of deities and spirits. Now, a growing number of glaciers are losing their equilibrium, or their capacity to build up enough snow and ice at high altitudes to compensate for the rate of melting at lower ones. After surveying the Himalayas for many years, the respected Chinese glaciologist Yao Tandong recently warned that, given present trends, almost two-thirds of the plateau's glaciers could well disappear within the next 40 years. With the planet having just experienced the 10 hottest years on record, the average annual melting rate of mountain glaciers seems to have doubled after the turn of the millennium from the two decades before. Moreover, temperatures on the Tibetan plateau are rising much faster than the global average. A good portion of the area's existing ice fields has been lost over the past four decades, and the rate of retreat has increased in recent years. The slow-motion demise of Baishui Glacier No. 1 will have far-reaching consequences. In the short run, there will, of course, be an abundance of water. But in the long run there will be deficits. These will have national security consequences as countries compete for ever scarcer water resources supplied by transnational rivers with as many as two billion users. It was not so long ago that the Tibetan Plateau was seen as a region of little consequence, save to those few Western adventurers drawn to remote regions that the early 20th-century Swedish explorer Sven Hedin once called the “white spaces” on the map. Today, these white spaces play a crucial role in Asia's ecology. Sadly, it may be too late to change the destiny of Baishui Glacier No. 1. But President Hu, by promising this week to try to cut carbon dioxide emissions per unit of gross domestic product and to increase the share of non-fossil fuels in primary energy consumption, signaled his willingness to act. China can't solve this problem alone, and President Obama's scheduled visit to Beijing in November presents an opportunity to forge a bilateral alliance on climate change. After all, the ice fields in the majestic arc of peaks that runs from China to Afghanistan are melting in large part because of greenhouse gases emitted thousands of miles away.