Now, some countries have begun turning this displacement into a positive learning experience by providing such migrants with temporary work permits to help them earn an income and acquire skills, making them more resilient when they return home.
"Extending work visas or granting temporary visas to people from countries ... hit by natural disasters is often used in ... Europe and North America," said Koko Warner, head of the Environmental Migration, Social Vulnerability and Adaptation Section at the UN University, and such initiatives were part of a "wider trend in managing the impacts of natural hazards and migration".
The US Immigration and Nationality Act allows Temporary Protected Status (TPS) to foreign nationals already in the US because of an environmental disaster, provided their country is unable to handle their return.
There are no international laws protecting people forced to move across borders by more intense natural disasters as a result of climate change, but Walter Kälin, Representative of the UN Secretary-General on the Human Rights of Internally Displaced Persons, cited the Finnish Aliens Act, which also "provides temporary protection (up to three years) in situations of mass displacement as a result of an environmental disaster."
He suggested that in the absence of such protection, initiatives like the TPS allowed by US could provide "inspiration" to countries to draw up laws offering temporary respite to people forced to move because of climate change.
Colombia has come up with an interesting alternative: in 2006, when the Galeras volcano in southwest Colombia erupted, the government set up a programme allowing several thousand affected people temporary migration to Spain, where they earned an income, mostly through agricultural work, for a period of six months, the UN Population Fund (UNFPA) noted in its recent annual report.
"Since then the programme has been expanded to include people in rural communities, where crops and land are vulnerable to floods and other natural disasters," UNFPA said. The programme is supported by the European Union.
Heavy rains, floods, earthquakes and volcanic eruptions in Colombia affected 1.5 million people in 2007, and at least 700,000 more in 2008, according to the UN Office for the Coordination of Humanitarian Affairs.
In Spain the Colombians acquired skills to help them diversify their income when they returned home, to "increase their resilience to environmental challenges, and offers them an alternative to permanent relocation," UNFPA commented. The six-month placement period also allowed enough time for the land affected by disaster in Colombia to recover.
Warner said such initiatives were "an important source of post-disaster rehabilitation", while UNFPA pointed out that "Mobility may therefore contribute to the adaptation of people affected by environmental change; conversely, immobility may increase people's vulnerability to environmental pressures."