Soaring food prices and the effects of global warming threaten to drive ever more people from their homes, the head of the United Nations refugee agency warned Tuesday.

The UNHCR said the number of refugees worldwide had risen for a second year running. Displaced people living outside their home country rose by almost 500,000 last year to 11.4m at the end of 2007, mainly due to the “volatile situation in Iraq”, the agency said in its annual Global Trends report.