Oxfam is warning that climate change represents a far greater threat to the world's poor than previously believed, because of the effects of extreme weather on harvests and food prices.
Allowing for inflation, the cost of staples could double over the next 20 years, it says, as yields become undependable and prices fluctuate wildly.
The charity's report comes hard on the heels of a statement from the United Nations that world leaders need to take swift action to avoid a food security crisis that could hit tens of millions of people.
"Political leaders must heed the warning of food agencies, stop dragging their feet and convene an emergency meeting of the Rapid Response Forum to prevent the threatened food price crisis becoming a reality," says Oxfam's Grow Campaign spokesperson, Colin Roche.
"Only the powerful G20 leaders have the political muscle to tackle the multiple problems - from speculation and bad biofuels policies to greenhouse gas emissions and lack of investment in agriculture - which are driving this crisis and making a future crisis all the more likely."
Last week, the World Bank reported that the price of maize and soybeans reached a record peak in July. It added that three-quarters of the price rise of internationally traded cereals will be passed on to domestic markets.
"The G20 has decided to wait for September's US crop report before deciding whether to take action on food prices but they must call it now before prices spiral out of control and push more people into hunger," says Roche.
"This 'wait and see' attitude is unacceptable, especially when the World Bank report has warned that prices are expected to remain high and volatile."