Former UN secretary-general Kofi Annan has criticised world leaders for failing to take bold action on climate change, which he said threatens to worsen the food crisis that has left a billion people hungry.

Speaking at Stanford University in California, the Nobel Peace Prize winner said rising temperatures and rainwater shortages are having a devastating effect on food production. Failing to address the problem will have repercussions on health, security and stability, he warned.

"Yet so far, our generation - my generation - of leaders, including those here in the United States, have failed to find the vision or courage to tackle it. This lack of long-term collective vision and leadership is inexcusable."

Mr Annan said the food crisis is an unconscionable moral failing and a brake on overall development.

He said the need for a universal and fair framework to address climate change is imperative. Without such action, "the result will be mass migration, growing food shortages, loss of social cohesion and even political instability", he said.

The bulk of Mr Annan's keynote speech to about 1,400 people addressed making the link between climate change and food supply and imploring action on that front. But he also touched on inequalities in agricultural policies, unfair trade rules and food price fluctuations.

"We urgently need to find ways of dampening extreme volatility in food prices, particularly the excessive speculation in agricultural commodities which causes it," he said.

The World Bank says rapidly rising food prices this year and last pushed an additional 70 million people into extreme poverty. One in seven people on the planet is hungry.

Mr Annan said as the population grows, greater prosperity will mean more people eating dairy and meat, and grain used to feed people will be increasingly switched to feed animals. Rising oil prices have brought competition from agro or biofuels, he said.

Last month, the Rome-based UN Food and Agriculture Organisation forecast improved prospects for world cereals production but warned there was uncertainty about the impact on food security because of the global economic slump and increased risks of recession. It also cited concern about irregular rains in West Africa in the 2011 cropping season and of severe monsoons in the Far East.