Environmental change and migration
The British Government Office for Science has published a report Foresight: Migration and Global Environmental Change (Financial Times article here) looking at displacement and migration, both internal and transnational, due to environmental factors up to 2050.
Moving can be to a place of greater vulnerability, as from drought devastated area to a flood plain, or it can be part of the solution. There is concern over vulnerable populations that can’t move. Effectively they are “trapped”.
17 million people were displaced by natural hazards in 2009 and 42 million in 2010 (this number also includes those displaced by geophysical events).
Future numbers are impossible to estimate.