"Global warming and extreme weather conditions may have calamitous consequences for the human rights of millions of people," said Kyung-wha Kang, the UN deputy high commissioner for human rights.

"Ultimately climate change may affect the very right to life of various individuals," she said, pointing to threats of hunger, malnutrition, exposure to disease and lost livelihoods, particularly in poor rural areas dependent on fertile soil.

Kang, a South Korean, said countries had an obligation "to prevent and address some of the direst consequences that climate change may reap on human rights".

This may include providing safe housing, ensuring good sanitation and water-drinking supplies, and making sure citizens have access to information and legal redress, and take part in decision-making, she said.

Environmental disasters and natural resource scarcity have long been seen as contributors to displacement, for instance in Sudan's Darfur region where 2.5 million people have been driven from their homes by conflict rooted in part in access to water.

But the United Nations has not yet expressly tackled climate change as a human right, for instance by enshrining the right to protection from its effects in an international convention.

Michelle Leighton, director of human rights programmes at the University of San Francisco's law school, told the conference pressures from global warming could also force would-be migrants into the hands of criminals.

Some three quarters of sub-Saharan Africa's agricultural drylands are now degraded to some degree, she said, pointing to West African countries such as Ghana, Senegal and Nigeria as most acutely vulnerable to climate change-related damage.

Many people in Somalia, Mali and Cape Verde will also have little option but to leave their lands in coming years, and many are likely to turn to human smugglers for help in accessing more prosperous countries in Europe and elsewhere, she said.

"This is a big business now," Leighton said. "If the climate change predictions come true, and we see much more pressure on agricultural lands in sub-Saharan Africa, we are likely to see an increase in illegal smuggling as well."

Gordon Shepherd of WWF International told the session that such pressures must be addressed by the international community as well as governments. "None of us will escape the effects of the disasters that are facing the future generations," he said.