Lester Brown writes:

The world is now facing a climate-driven shrinkage of river-based irrigation water supplies. Mountain glaciers in the Himalayas and on the Tibet-Qinghai Plateau are melting and could soon deprive the major rivers of India and China of the ice melt needed to sustain them during the dry season. In the Ganges, the Yellow, and the Yangtze river basins, where irrigated agriculture depends heavily on rivers, this loss of dry-season flow will shrink harvests.

The world has never faced such a predictably massive threat to food production as that posed by the melting mountain glaciers of Asia.