Low end is 5 mil, upper is 1 bil. Most commonly cited figure and the basis for most extrapolation is 200 million. However that's still a lot. To put it in perspective:
"The current global estimate is that there were around 272 million international migrants in the world in 2019, which equates to 3.5 per cent of the global population"
"This is a daunting figure; representing a ten-fold increase over today’s entire documented refugee and internally displaced populations. To put the number in perspective it would mean that by 2050 one in every 45 people in the world will have been displaced by climate change."
To be clear, these figures represent how many people will have relocated by that point in time, not the number of people actively relocating at that point in time. Today, about 3.5% of the global population lives in a country other than the one they were born in. This prediction is that by 2050 that figure will have an extra 3% on top attributable to climate change.
"The current global estimate is that there were around 272 million international migrants in the world in 2019, which equates to 3.5 per cent of the global population"
UN World Migration Report 2020 - https://www.un.org/sites/un2.un.org/files/wmr_2020.pdf
Back to the 200 million figure:
"This is a daunting figure; representing a ten-fold increase over today’s entire documented refugee and internally displaced populations. To put the number in perspective it would mean that by 2050 one in every 45 people in the world will have been displaced by climate change."
IOM Migration & Climate Change - https://www.ipcc.ch/apps/njlite/srex/njlite_download.php?id=...
To be clear, these figures represent how many people will have relocated by that point in time, not the number of people actively relocating at that point in time. Today, about 3.5% of the global population lives in a country other than the one they were born in. This prediction is that by 2050 that figure will have an extra 3% on top attributable to climate change.