World grain reserves are so dangerously low that severe weather in the United States or other food-exporting countries could trigger a major hunger crisis next year, the United Nations has warned. Failing harvests in the US, Ukraine and other countries this year have eroded reserves to their lowest level since 1974. The US, which has experienced record heatwaves and droughts in 2012, now holds in reserve a historically low 6.5% of the maize that it expects to consume in the next year, says the UN.

"We've not been producing as much as we are consuming. That is why stocks are being run down. Supplies are now very tight across the world and reserves are at a very low level, leaving no room for unexpected events next year," said Abdolreza Abbassian, a senior economist with the UN Food and Agriculture Organisation (FAO). With food consumption exceeding the amount grown for six of the past 11 years, countries have run down reserves from an average of 107 days of consumption 10 years ago to under 74 days recently.

Prices of main food crops such as wheat and maize are now close to those that sparked riots in 25 countries in 2008. FAO figures released this week suggest that 870 million people are malnourished and the food crisis is growing in the Middle East and Africa. Wheat production this year is expected to be 5.2% below 2011, with yields of most other crops, except rice, also falling, says the UN.