1 The latest report by the Intergovernmental Panel on Climate Change (IPCC) has confirmed that environmental changes are transforming our planet. The international community is now seeking to contain and anticipate future changes in the world climate that may, over time, displace large sections of the world population.

Environmental migration is difficult to identify

2 Is it possible to distinguish between migration for environmental reasons and migration related to other factors? Migration is “environmental” when a population is displaced primarily (if not solely) because of a change in the environment [1]. If climate change is involved, the term “climate migration” is used, and the people who move under such circumstances are often referred to as “climate refugees”, though the term “refugee” may not be entirely appropriate in this case (Box 1). From the beginning of human history, environmental changes have forced people to leave their homes, but in recent decades the number of potential migrants has risen sharply because populations are increasingly concentrated in zones now at risk from climate change.

3 Whether or not migration is linked to environmental degradation, it results from complex decision-making processes. The decision to leave may well be linked to the environment, but people contemplating a move also consider other aspects of their situation that may be economic (resources for the journey, prospects for employment at their destination), social (opportunities for integration at their destination) or even symbolic (attachment to their home, anticipated improvement in their social status). In situations other than sudden natural disasters, it may be hard to distinguish migrations due primarily to the environment from those with mainly economic or political causes (Box 2).

4 The environmental factors involved in population mobility are also multiple. As Jason Bremner and Lori M. Hunter note,[1] there is a “continuum of environmental pressures that contribute to migration”. These include long-term changes, such as soil degradation and decreasing land availability which result in gradual out-migration over time; medium-term pressures such as prolonged drought, leading to large-scale out-migration; and sudden, violent events resulting in the forced but perhaps temporary displacement of an entire population.

Migration is not the only response to environmental variations

5 Even in cases of extreme environmental change such as severe drought or flooding, the people directly affected may not migrate but rather receive assistance from family members settled elsewhere. Monetary transfers from family members who migrated earlier for economic reasons help local populations cushion the shocks of environmental events. The connection between environment and migration is therefore not easy to capture, given that some people can turn to different places or branches of the family for assistance in response to seasonal or exceptional climatic events. Diversification strategies in terms of resources and activities are means of ensuring economic security. The lifestyle of nomadic populations is, by definition, one of mobility, but this is true for other populations too. Fishermen regularly move from place to place, since seasonal or occasional migrations are, for them, a way of preserving spawning zones and maximizing their catch over the long term. Sheep and cattle herders often migrate on a seasonal basis, pasturing their herds over extended territories in the wet season and around watering spots in the dry season. Farmers practice similar systems involving a variety of soils and crops. At the family scale, having activities in different ecosystems is a way of minimizing economic risk. With these facts in mind, how reliable are the estimates of number of persons annually displaced by “disasters”? (Box 3)

Disasters trigger a wide variety of displacements

6 In contrast to gradual environmental changes, “natural” [2] or technological disasters trigger emergency movements. Such movements are more clearly cases of environmental migration, but this does not mean they are easy to quantify.

7 Some migrations are immediate or, if the population can be forewarned, may actually precede the disaster (this holds for cyclones). In other situations, residents move out of the affected area some time after the disaster occurs (for example, Fukushima, where the perimeter of the exclusion zone was later extended). Some displacements are short term; others involve movements back and forth; yet others are true migrations. Most – though not all – occur on a local scale. During the 1984 technological disaster in Bhopal, India (toxic gas leakage from a pesticide factory), residents who did not know what was happening stayed put while others fled in panic; many of those who left returned in the next few days without knowing whether it was safe to do so; some then left a second time. The reaction of residents in the northeastern Indian state of Odisha when Cyclone Phailin hit in 2013 was quite different, as they had been forewarned early enough for protection measures to be taken. Nearly 600,000 persons were evacuated – by force in some cases – to nearby areas, still within the risk zone, where they were sheltered in concrete structures built in response to the 1999 “super cyclone” that killed 10,000 persons in the same region. When an extreme event is over, the speed and intensity with which inhabitants return varies by socioeconomic level and the magnitude of destruction, as shown for Hurricane Katrina in the United States. [3] Disasters such as the 2011 tsunami and the resulting nuclear accident at Fukushima, both caused by the Great East Japan Earthquake, gave rise to erratic population displacement, especially in Fukushima prefecture because people living near the nuclear plant received only fragmentary information that was constantly being revised. In the contaminated zone, persistently high radiation levels made a return impossible. Elsewhere, residents were only gradually able to return home as reconstruction work progressed. The three disasters of 2011 – earthquake, tsunami and nuclear accident – are estimated to have displaced half a million people, but again the data should be viewed with circumspection (Box 4).

Figure 1

Number of persons displaced by disasters from 2008 to 2013

Number of persons displaced by disasters from 2008 to 2013

The authors themselves explain that these figures are likely to underestimate environmental emigration as they are based primarily on large-scale disasters. It should also be noted that estimates for the same disaster may differ substantially. Such figures have a high margin of uncertainty.

Is mobility a strategy for adapting to climate change?

8 With regard to future environmental migration, it is important to distinguish between high levels of risk and high intensities of actual migration.

9 Global warming is likely to raise sea levels, affecting populations in coastal regions most severely. In the IPCC’s most pessimistic scenarios, the sea will rise by nearly one meter by the end of this century and by over three meters by 2300. [4] Coastal urbanization is a factor of vulnerability: many heavily populated urban areas have developed on or near coasts. Of the world’s more than 450 cities with over 1 million inhabitants in 2011, home to a total of 1.4 billion people, an estimated 60 %, or slightly under 900 million, are exposed to a high risk of natural disaster. [5] It is now possible to map the areas at risk for probable sea level rises (see the examples of the Gulf of Guinea and the Netherlands in Figure 2). It has been estimated that 10 % of the world’s population live less than 10 meters above sea level across a territory representing only 2 % of the earth’s total surface. We know that the very existence of some Pacific Ocean countries is threatened, so the question of environmental migration is international in scale.

Figure 2

Examples of heavily populated areas threatened with a 3-meter rise in sea levels

Examples of heavily populated areas threatened with a 3-meter rise in sea levels

10 The causes of global warming are to some degree international, and negotiations to slow down these ongoing processes take place in the international arena; yet the effects of climate change are often quite localized and take numerous different forms: some countries and populations are much more vulnerable than others. The threat of natural disasters may give rise to permanent migration, as in Bangladesh, where families are leaving highly exposed Ganges delta lands for the slums of Dhaka. In northeast India, by contrast, concrete shelters provide short-term protection to local populations during the frequent cyclones. The Netherlands, for its part, is implementing a vast public works programme to combat rising sea levels. Clearly then, migration – whose economic and social costs are immense – is not the only possible response to the effects of climate change.