Climate change bringing floods and drought, growing biofuel demand and national policies to protect domestic markets could drive up global food prices and threaten long-term food security, the United Nations said.

High and volatile food prices are a growing global concern, partly fuelling the protests that toppled the rulers of Tunisia and Egypt this year. The aftershocks have been seen across North Africa and the Middle East from Algeria to Yemen.

Periods of price volatility are not new to agriculture, but recent price shocks triggered by extreme weather and increasing use of grains to produce energy have caused great concern, the UN’s Food and Agriculture Organization said.

“There are fears that price volatility may be increasing,” the FAO said in its State of Food and Agriculture report.

The growing influence of commodities markets and “counterproductive ‘beggar-thy-neighbour’ policy responses (to high prices)… may exacerbate international market volatility and jeopardize global food security,” it said.