This year Russia is expect its wheat crop to be 10 to 20% below normal. As a result it has suspended its usual export of wheat, one of its best cash earners after oil and gas. Secondary to that world wheat prices have risen. Of course that helps farmers in areas where the wheat crop is good this year, like the United States.
This event is driven by high temperatures and drought. That in turn may be driven by global warming, but specific events are hard to attribute to slow, general trends.
The wheat situation is a reminder that the Earth is overpopulated with humans. Food production is a tricky business. Drought has tended to have the largest impact on food production since the invention of pesticides, but fungus, viruses, insects, weeds, and even rodents still compete with humans for the crops we try to raise. There are multiple points of failure available, and where there are multiple points of failure, failures will occur.
The United States is no longer a net food exporter. True, we are far from endangered in the short run. Over half of Americans are fat, so calorie intake could probably be cut something like 25% for our population as a whole before any widespread detrimental health effects set in.
Looking ten to twenty years down the road, however, the situation could turn far more serious as both the global and U.S. populations continue to rise. As food prices rise (after a century of low prices by most measures) more land may be brought into production, and yields would be expected to continue to show technology-based increases. But it is hard to plot out a scenario where food supplies grow as fast as the population.
We can count on global warming, but we don't know where and when its local effects will strike. If multiple major grain exporting nations are hit by simulaneous droughts lasting two years or longer, we could see famines on a global scale.
The only real long term solution is a global population policy. Let me be clear: over the next century the human global population should be reduced to about 3 billion people. Carbon dioxide is not the problem. Too many people is the problem.
More on the global population problem:
Food and Population [January 31, 2007]
Population and Global Warming [January 25, 2007]
Population Incentives [January 6, 2007]
Population, Population, Population [December 13, 2006]
China's Population Issues [link to People's Daily Online]