from the Independent:
Rising temperatures between 1981 and 2002 caused aloss in production of wheat, corn and barley that amounted in effect to some 40 million tons a year – equivalent to annual losses of some £2.6bn.
Although these numbers are not large compared to the world-wide production of cereal crops, scientists warned that the findings demonstrated how climate change was already having an impact on the global production of staple foods. “Most people tend to think of climate change as something that will impact the future, but this study shows that warming over the past two decades has already had real effects on global food supply,” said Christopher Field of the Carnegie Institution in Stanford, California.
for abstract of paper, and link to full paper (for which need subscription):
Global scale climate–crop yield relationships and the impacts of recent warming
Changes in the global production of major crops are important drivers of food prices, food security and land use decisions.