While the American press (and blogosphere) has been mesmerized by the Democratic horse race, Egyptians have been protesting and rioting this week over, among other things, rising food prices. This is just a sign of things to come, warns the United Nations.

Sir John Holmes, undersecretary general for humanitarian affairs and the UN's emergency relief coordinator, told a conference in Dubai that escalating prices would trigger protests and riots in vulnerable nations.

"The security implications [of the food crisis] should also not be underestimated as food riots are already being reported across the globe," Holmes said. "Current food price trends are likely to increase sharply both the incidence and depth of food insecurity."

As well as this week's violence in Egypt, the rising cost and scarcity of food has been blamed for:

· Riots in Haiti this week that killed four people
· Violent protests in Ivory Coast
· Price riots in Cameroon in February that left 40 people dead
· Heated demonstrations in Mauritania, Mozambique and Senegal
· Protests in Uzbekistan, Yemen, Bolivia and Indonesia

The biggest challenge to addressing this problem? Climate change, he says.