Human migration is an activity that is as old as humanity itself. Yet it remains a sensitive and politically charged subject, creating tensions in societies that experience it. It is closely linked to economic, environmental, demographic and political factors. It has become a conspicuous feature of the world political and demographic scene, with an estimated number of 22 million migrants in the past year. It shows every sign of accelerating in the future, not only because of poverty, civil war and politics, but also from environmental reasons that, in the future, may cause still larger–scale migration. Migration will be influenced by a host of such factors as climate change, sea–level rise, desertification, and environmental degradation generally.