The policies of the states of origin or destination, as well as the transit states, affect the migratory movements.
Transnational networks of migrants and diaspora are also elements that can shape the migration.
In the latest publication by Riosmena, Nawrotzki & Hunter, the authors specify that international migration due to environmental reasons can increase under specific circumstances and following existing networks that could reduce the costs of migration.In general, most scholars agree it is unlikely to occur a massive international flow of migrants, and most migrants will either move within their own country and/or region.
There are several historical examples of the relationship between environment/climate and migration. For example, in his book Economy and Society, Max Weber refers mentions that "the flooding of the Dollart [at the mouth of the Ems river near the Dutch-German border] in 1277 had historical significance as a stimulus to the beginning of certain migrations of considerable importance".