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By Dominic Kniveton and Max Martin, for SciDev.Net
What do farmers in the tropics do when their land remains parched for years, or the delta islands on which they live are flooded more frequently because of a changing climate?
If you think, like many still do, that they either stay put in increasing hardship or abandon their homes and emigrate to developed countries, it is time to think again.
People do migrate when faced with rapid and uncertain changes in their environment, but this is largely within their own country and sometimes within their home region. Such movements usually follow, build on or tweak established pathways of migration.
And most of the time, they eventually lead back home — people tend to move back and forth, looking for more productive livelihoods.
The popular media sometimes set out vivid future scenarios of people abandoning their homes and fleeing en masse to faraway places. But there is no hard evidence to support such forecasts.
Evidence from Bangladesh
Internal migration is a trend we observed through ongoing research in Bangladesh carried out alongside the University of Dhaka's Refugee and Migratory Movements Research Unit.
In its first phase, the study, funded by the Climate and Development Knowledge Network, examined 14 villages in three districts: one largely affected by drought, one by flooding and one by cyclones.
Through interviews and focus group discussions, we probed what goes on inside people's minds when they encounter these stresses and shocks.
In all of the locations sampled, people reported broadly similar trends: droughts or floods becoming more common, rain patterns becoming less predictable, riverbanks eroding faster, storm surges getting more serious, land and water becoming increasingly salty and midday temperatures rising. Often, these observations chimed with scientific data.
At the same time, economic opportunities are changing in Bangladeshi cities, especially the booming metropolis of Dhaka. There is a trend of people leaving unproductive farms and joining the urban labour force.
Men often find work as construction labourers or in the informal sector as rickshaw pullers or street vendors, while the educated among them may join the growing services industry. Many women join garment factories.
With better education and skills training, these migrants can make better use of the emerging economic opportunities.
Some of the villagers told us that, while they regard environmental events as acts of God, they believe they can proactively minimise or offset their impacts.
For instance, when farmland gets flooded or becomes salinised, the farmer could go to a town, pull a rickshaw or sell plastic toys to earn money for a while, and then return home hoping for a better season.
From our preliminary work, we get a sense that, faced with change, people are increasingly seeking diverse livelihood strategies — different ways to make a living. This includes migrating to locations within the country that are well-established as well as new to them. And while some do migrate internationally, long hauls are rare.
In general, the villagers see migration as a normal livelihood strategy — there is nothing dramatic about it.
Migrants almost never give climate as the reason for their movements. Yet, in reality, migration is working as an effective adaptation strategy to climate change, helping people prepare for and recover from the impacts and uncertainties of environmental stress.
But migrants get little support to move out of vulnerable areas, to find new settlements or to return home. They are seen as an outcome of the failures of rural development, not as winners of new work opportunities in cities or as evidence of successful adaptation.
So they often end up living in slums or informal settlements on the fringes of growing cities, exposed to flooding and other hazards. Local governments often fail to provide safe environments and facilities.
Supporting controlled migration
Much discussion about climate-based migration, even in policy circles, still tends to revolve around the notion that when the climate gets hostile people abandon their homes and flee.
A 2011 report commissioned by the Foresight programme of UK Government Office for Science argued that policymakers should help poor people move away from dangerous areas as a way of coping with climate change. Otherwise, it says, people could inadvertently migrate toward vulnerable areas or remain trapped in hazardous conditions. 
But policies that restrict migration could, in effect, worsen such situations.
The best bet is to open up existing migration routes, acknowledge migration as an acceptable and effective form of adaptation and facilitate it whenever it is possible and safe.
Policies should be designed to support internal movements for short or long periods as a form of adaptation to climate change. To do this, it helps to see migration as a positive response.
Dominic Kniveton is professor of climate science and society at the University of Sussex, UK. Max Martin is a doctoral candidate at the university. Max can be contacted at email@example.com.
This article first appeared on SciDev.Net.
 Foresight Migration and Global Environmental Change (Government Office for Science, 2011)