Fast-growing cities are also competing with farmers for irrigation water. In areas where all water is being spoken for, such as most countries in the Middle East, northern China, the southwestern United States, and most of India, diverting water to cities means less irrigation water available for food production. California has lost perhaps a million acres of irrigated land in recent years as farmers have sold huge amounts of water to the thirsty millions in Los Angeles and San Diego.
The rising temperature is also making it more difficult to expand the world grain harvest fast enough to keep up with the record pace of demand. Crop ecologists have their own rule of thumb: For each 1 degree Celsius rise in temperature above the optimum during the growing season, we can expect a 10 percent decline in grain yields. This temperature effect on yields was all too visible in western Russia during the summer of 2010 as the harvest was decimated when temperatures soared far above the norm.
Another emerging trend that threatens food security is the melting of mountain glaciers. This is of particular concern in the Himalayas and on the Tibetan plateau, where the ice melt from glaciers helps sustain not only the major rivers of Asia during the dry season, such as the Indus, Ganges, Mekong, Yangtze, and Yellow rivers, but also the irrigation systems dependent on these rivers. Without this ice melt, the grain harvest would drop precipitously and prices would rise accordingly.
And finally, over the longer term, melting ice sheets in Greenland and West Antarctica, combined with thermal expansion of the oceans, threaten to raise the sea level by up to six feet during this century. Even a three-foot rise would inundate half of the riceland in Bangladesh. It would also put under water much of the Mekong Delta that produces half the rice in Vietnam, the world's number two rice exporter. Altogether there are some 19 other rice-growing river deltas in Asia where harvests would be substantially reduced by a rising sea level.
The current surge in world grain and soybean prices, and in food prices more broadly, is not a temporary phenomenon. We can no longer expect that things will soon return to normal, because in a world with a rapidly changing climate system there is no norm to return to.
The unrest of these past few weeks is just the beginning. It is no longer conflict between heavily armed superpowers, but rather spreading food shortages and rising food prices -- and the political turmoil this would lead to -- that threatens our global future. Unless governments quickly redefine security and shift expenditures from military uses to investing in climate change mitigation, water efficiency, soil conservation, and population stabilization, the world will in all likelihood be facing a future with both more climate instability and food price volatility. If business as usual continues, food prices will only trend upward.