How many climate migrants will there be around the year 2050? We did some research:
The world bank estimates 140 million internal migrants in Sub-Saharan Africa, Latin America and South Asia by 2050.
A United Nations report of 2009 estimated the number of people to be displaced internally in 2045 by desertification alone around 135 million.
The UN International Organization for Migration forecasts 200 million internal and international (permanent and temporary) environmental migrants by 2050.
A paper from June 2017 (by Geisler et al) mentions 1.4 billion people that could be climate refugees by 2060 due to rising ocean levels (alone!). A number that societies might not be able to support: “The colliding forces of human fertility, submerging coastal zones, residential retreat, and impediments to inland resettlement is a huge problem. We offer preliminary estimates of the lands unlikely to support new waves of climate refugees due to the residues of war, exhausted natural resources, declining net primary productivity, desertification [and] urban sprawl…”
12 million hectares of productive land become barren every year due to desertification and drought (alone), while food production needs to increase by 70% in 2050 to feed the entire world population. Drought, water scarcity and destruction of natural resources because of climate change (and overpopulation, etc.) might lead to conflict. The UNCCD reminds that 40 per cent of all intrastate conflicts in the past 60 years are linked to the control and allocation of natural resources.
And for those that like smaller numbers: In 2017 there were (already) 24.2 million new displacements because of disasters.
And for comparison of the above numbers: In 2016 international migration numbered around 260 million people.