For the 193 national delegations gathering in Copenhagen for the U.N. Climate Change Conference in December, the reasons for concern about climate change vary widely. For delegations from low-lying island countries, the principal concern is rising sea level. For countries in southern Europe, climate change means less rainfall and more drought. For countries of East Asia and the Caribbean, more powerful storms and storm surges are a growing worry. This climate change conference is about all these things, and many more, but in a very fundamental sense, it is a conference about food security.

We need not go beyond ice melting to see that the world is in trouble on the food front. The melting of the Greenland and West Antarctic ice sheets is raising sea level. If the Greenland ice sheet were to melt entirely, sea level would rise by 23 feet. Recent projections show that it could rise by up to 6 feet during this century.

The world rice harvest is particularly vulnerable to rising sea level. A World Bank map of Bangladesh shows that even a 3 foot rise in sea level would cover half of the riceland in this country of 160 million people. It would also inundate one third or more of the Mekong delta, which produces half of the rice in Vietnam, the world’s number two rice exporter. And it would submerge parts of the 20 or so other rice-growing river deltas in Asia.

The worldwide melting of mountain glaciers is of even greater concern. The World Glacier Monitoring Service in Switzerland has recently reported the 18th consecutive year of shrinking mountain glaciers. Glaciers are melting in the Andes, the Rocky Mountains, the Alps, and throughout the mountain ranges of Asia.

It is the disappearing glaciers in the Himalayas and on the Tibetan Plateau that are of most concern, because their ice melt sustains the flow of the major rivers of India and China-the Indus, Ganges, Yangtze, and Yellow rivers-during the dry season. This ice melt thus also sustains the irrigation systems that depend on these rivers.