(Seto et al., 2011). New migrants to these cities tend to be highly exposed to climate stresses, including storm surge and sea level rise, because they often tend to move to locations, such as floodplains and hill slopes, that are highly exposed to environmental hazards. They also tend to be more susceptible to being harmed because, within receiving cities, migrants are typically poorer than resident populations and in many cases have little knowledge of local environmental risks in a new city and may therefore be unaware of the risks of moving to areas that lie within flood plains or are otherwise hazard-prone. These interrelated trends suggest that climate change–related threats to human security may be just as prominent in areas of migration destination, particularly urban ones that receive large numbers of immigrants, as in areas of emigration. Migrants into new areas may also place strains on governmental or other resources and may potentially contribute to new types of conflicts, particularly within receiving areas that are already under social stress (Reuveny, 2007). Large flows of immigrants can also create or contribute to security threats in sensitive border or transition regions.
Although much of the discussion on climate change and migration emphasizes displacement or unplanned migration, it is also important to recognize that migration is an adaptation strategy to environmental change that may be necessary and even beneficial under some circumstances (McLeman and Smit, 2006; Tacoli, 2009; Black et al., 2011c; Foresight, 2011). In some cases migration may reduce security threats by taking pressure off local resources or by bringing new revenue into a local area as the result of international remittances. Paradoxically, climate change may also undermine options for adaptation via its effects on the assets and other characteristics of households. Migration typically requires a significant outlay of financial resources, yet actions needed to cope with environmental changes (e.g., selling land or livestock) can reduce a household’s assets to the point that family members who could adapt by migrating may not have the resources to do so. Those households or individuals who cannot migrate out of a region that is undergoing environmental change are among the most vulnerable (Black et al., 2011c). Regions with large concentrations of “trapped” populations that are unable to migrate may pose a new type of human security threat. When an extreme climate event occurs, these “poorest of the poor” may end up trapped in environmentally degraded areas, creating situations that are ripe for humanitarian catastrophe (Foresight, 2011).
Extreme political instability, particularly when it substantially weakens or causes the overthrow or collapse of a strategically important regime or when it results in the onset of civil war, may have significant security