BEIRUT - If rising sea levels force the people of the Maldive Islands to seek new homes, who will look after them in a world already turning warier of refugees?

The daunting prospect of mass population movements set off by climate change and environmental disasters poses an imminent new challenge that no one has yet figured out how to meet.

People displaced by global warming -- the Christian Aid agency has predicted there will be one billion by 2050 -- could dwarf the nearly 10 million refugees and almost 25 million internally displaced people already fleeing wars and oppression.

"All around the world, predictable patterns are going to result in very long-term and very immediate changes in the ability of people to earn their livelihoods," said Michele Klein Solomon of the International Organisation of Migration (IOM).

"It's pretty overwhelming to see what we might be facing in the next 50 years," she said. "And it's starting now."

People forced to move by climate change, salination, rising sea levels, deforestation or desertification do not fit the classic definition of refugees -- those who leave their homeland to escape persecution or conflict and who need protection.

But the world's welcome even for these people is wearing thin, just as United Nations figures show that an exodus from Iraq has reversed a five-year decline in overall refugee numbers.

Governments and aid agencies are straining to cope with the 10 million whose plight risks being obscured by debates over a far larger tide of economic migrants -- and perhaps future waves of fugitives from environmental mayhem.

HARSHER CLIMATE

The United Nations High Commissioner for Refugees (UNHCR), which marks World Refugee Day on Wednesday, says the global political climate for refugees has already become harsher.

"They used to be welcomed as people fleeing persecution, but this has been changing -- certainly since 9/11, but even before then," said William Spindler, a UNHCR spokesman in Geneva.

"Growing xenophobia, intolerance, political manipulation by populist politicians who mix up the issues -- the whole debate on asylum and migration has been confused," he said.

People fleeing threats at home and those seeking a better life could be in the same group washing up on a Spanish beach, but Spindler said it is vital to keep the distinction between them to provide effective protection to those who need it.

Whatever their motives, migrants deserve to be treated with dignity and as human beings, he added. "We have seen people in the Mediterranean in boats or hanging onto fishing nets for days while states discuss who should rescue them."

Before sectarian violence exploded in Iraq last year, global refugee numbers had been shrinking. The Taliban's overthrow in Afghanistan, along with peace deals in trouble-spots like Congo, Liberia, Angola and southern Sudan, had allowed millions to return home -- although 2.1 million Afghans have yet to do so.

"I'm not suggesting that life is all beautiful in those countries, but there have been advances," said Joel Charny, vice-president of Washington-based Refugees International.

"The big exception is Iraq, the fastest-growing refugee crisis in the world," he said. "Everyone's fleeing. It's really broad-based insecurity displacing people in Iraq and outside."

The UNHCR says 2.2 million Iraqis have fled abroad and over two million have left their homes inside the country, where they are much harder to track or assist than those overseas.

INTERNALLY DISPLACED

Around the world, nearly 25 million people are internally displaced -- fleeing for the same reasons as refugees, but lacking international recognition or protection.

While Iraq and Darfur often hit the headlines, aid officials worry about the "forgotten crises" that uproot people within national borders, often far from television cameras.

"Hardly anyone is concerned about the Central African Republic," said Sarah Hughes, UK director of the International Rescue Committee (IRC). "And in Chad for instance, refugees from Darfur get three times more provision than Chadian displaced."

Recognizing the scale of internal population upheavals, the UNHCR last year took under its wing some 13 million displaced people, many of whom had to be reached in conflict zones.

"In Darfur, the problem is not funding but security and access to the people we are trying to help," said Spindler.

The bloodshed in Iraq has made it a virtual no-go zone for international humanitarian staff, but aid workers also grapple with violent environments anywhere from Afghanistan to Colombia.

"The biggest challenge is security, the shrinking of humanitarian space," said the IRC's Hughes.

HOSTILITY

Refugees may also feel the world has less room for them as they try to cross borders into countries where hostility to migrants of all sorts has grown, compared with the Cold War era when fugitives from communism won sympathy and asylum.

"The reaction now is skepticism," said Charny. "It's: 'Who is this scam artist trying to get a job in our country?'"

North Koreans fleeing to China or Zimbabweans crossing illegally into South Africa are widely treated as economic migrants though many may also be escaping persecution, he said.

"We have to maintain a refugee protection regime that doesn't just assume everyone is an illegal economic migrant," Charny added. "That tendency exists in the industrialized countries and in the wealthier countries of the global south."

With those escaping environmental upsets likely to swell flows of migrants and refugees, any quest for legal definitions tying governments to new obligations might prove tricky.

"That's not to say that practical arrangements can't be found to deal with this," said the IOM's Klein.

The focus should be on contingency plans for nightmare scenarios that could prove all too real, Charny agreed.

"How will we approach displacement when, say, the Maldives go under?" he asked. "We have to plan for it, but in a way that doesn't lead us all to start jumping out of windows."

© Reuters 2007.