Is there migration that is caused exclusively by climate change or are causation far more complex, even in situations where climate change seems to play a role?
As far as I know, climate change has an indirect effect on migration, mainly through economical issues. For example, there has been droughts in the past years in Iran, which affected the agriculture industry, which uses outdated technologies and demands huge amounts of water. Farmers living in rural areas can no longer support their families, so they move to cities, hoping to find a job. This trend is clearly visible in the latest census.
River banks erosion is a problem in Coastal areas of Noakhali and people migrated. Peoples from other district also migrated to Noakhali as a result of erosion.
There are many low-lying countries, especially in the Asia-Pacific region, where countries are being flooded by rising sea levels, thereby leading to migration, if at all possible.