GENEVA - Environmental disasters sparked by climate change will increase the number of people seeking to migrate to richer countries from poorer parts of the world, U.N. refugee chief Antonio Guterres warned on Monday.

Speaking to the executive committee of his agency, the UNHCR, the former Portuguese prime minister called on the international community for greater efforts to tackle the problems sparking migration flows.

"Almost every model of the long-term effects of climate change predicts a continued expansion of desertification, to the point of destroying livelihood prospects in many parts of the globe," Guterres said.

"And for each centimetre the sea level rises, there will be one million more displaced.

"The international community seems no more adept at dealing with these new causes (of migration) than it is at preventing conflict and persecution," he said.

The Geneva-based UNHCR says that by the end of 2006 it was helping to look after some 32.9 million people around the world who have fled already from environmental disasters, wars, political and ethnic oppression and extreme poverty.

Of these, nearly 10 million have crossed international borders and are officially regarded as refugees under U.N. terminology, 13 million are internally displaced, or IDPs, within their own countries, and 5.8 million are stateless.

The remaining 4 million include people in the process of being repatriated or whose exact status has to be determined.

Guterres said the numbers of people fleeing conflict and persecution, which had been in decline for several years earlier in the century, had started to climb again in 2006 and the trend was growing this year.

Crises such as Iraq -- where over 4 million uprooted people inside and outside the country made up the largest-ever population of "urban refugees" -- and around Somalia in the Horn of Africa were adding daily to the totals.

Guterres, whose formal title is United Nations High Commissioner for Refugees, said that around the globe the dramatic growth in migration was also driven by a desire "simply to avoid dying of hunger".

But the varying causes of the flow were increasingly related to each other and required not only better understanding of the refugees and IDPs themselves but "demand-targeted strategies and innovative answers" from the world at large.

More international burden-sharing was needed through resettlement of refugees in third countries.