Climate Agreement Needed to Prevent Migration: UN

"Populations will relocate due to more extreme weather, including prolonged droughts, intensive storms, wildfires," he said.

The threat is already visible in the "devastation" wrought on New Orleans by Hurricane Katrina in 2005, Ban said, adding that perennial floods displace millions in countries like Bangladesh whilst rural areas in Africa are emptying from desertification.

"We need action and agreement in Copenhagen. We will continue to push for the most ambitious targets and the most ambitious agreement possible," he said.

The December 7-18 talks in Copenhagen aim to produce a treaty that will take effect after 2012 when current pledges of the Kyoto Protocol expire, setting medium- and long-term goals for taming global warming.

An EU summit last week agreed that developing nations will need 146 billion dollars (100 billion euros) per year by 2020 to tackle climate change, but failed to nail down how much aid it would provide.

At the immigration forum in Athens, Ban said more people were on the move than ever before, also spurred forward by poverty and war.

"Today, the number of international migrants is greater than at any time in history, with 214 million people living outside their country of birth," he said.

The financial crisis exacerbated matters as migrant workers were among the first hit with layoffs, impacting the vital income sent to families back home.

"The World Bank projects that remittance flows are likely to fall seven to 10 percent in 2009," Ban said, later admitting that "no global regulatory framework exists" to force credit transfer agencies that often handle payments to reduce their charges.

The informal two-day Global Forum on Migration and Development (GFMD) opened in Athens on Wednesday with policymakers from over 130 countries discussing the economic impact of immigration and proposals on how to improve migrants' integration.

Officials from over 40 international and regional organisations are also present.

A separate but affiliated "civil society" conference uniting staff from 250 non-governmental organisations and businesses was held on Monday and Tuesday.

"Our goal is to harness the power of migration to reduce poverty and inequality," Ban said.

Another conference aim is to dispel myths about migration -- among them the widely held notion that migrants steal jobs from locals.

"European countries are very aware of their demographic trends," said Hania Zlotnik, a UN population expert at the organisation's Global Migration Group (GMG).

"They are likely to need more workers in the future, they're not ready to close the doors to migration in a total way," she said.

The annual forum series began in 2006 following a proposal from former secretary general Kofi Annan.

Greek leftist organisations and migrant and citizens' groups have criticised the event, arguing that governments should be focusing on the treatment of migrants rather than their economic integration.

A protest march against the conference is to be held later on Wednesday.