Water. As Brahma Challaney notes:
The Tibetan plateau’s vast glaciers, huge underground springs and high altitude make Tibet the world’s largest freshwater repository after the polar icecaps. Indeed, all of Asia’s major rivers, except the Ganges, originate in the Tibetan plateau. Even the Ganges’ two main tributaries flow in from Tibet.With industrialization and population growth, China and India are very water-stressed, to be point that per-capita, Chinese will soon have only as much as water as Saudi Arabia. And so, China has been damming Tibetan waters and plans are to reroute them northward, into China:
China has been damming most international rivers flowing out of Tibet, whose fragile ecosystem is already threatened by global warming. The only rivers on which no hydro-engineering works have been undertaken so far are the Indus, whose basin falls mostly in India and Pakistan, and the Salween, which flows into Burma and Thailand ... The issue now is not whether China will reroute the Brahmaputra, but when. Once authorities complete their feasibility studies and the diversion scheme begins, the project will be presented as a fait accompli . China already has identified the bend where the Brahmaputra forms the world’s longest and deepest canyon – just before entering India – as the diversion point.At which point, northern India will become a desert. Nuclear-armed India.
Because India is water-stressed, many of the inter-state water disputes that play out in the American West also play out in India. When I was in college in India, we'd taken a trip to Karnataka, a neighboring state , when some bureaucrat changed some interpretation of some long-standing water agreement between the Tamil Nadu (the state I was living in) and Karnataka (the one I was visiting). Karnataka erupted in riots and it was dangerous to be a Tamil in Karnataka at that time. We moved a few of our Kannada-speaking classmates to the front of the bus to talk to any one who stopped us and quickly made our way back home. And that was just between states in one, pretty unified, country. Water is very, very personal.
What is frightening is that even if the cause of desertification of northern India is global warming, and not China, Chinese actions will serve as a nice repository of blame. It's hard to wage war on global warming, but war on China will be quite easy to imagine. And politicians, you can be sure, will take the bait.