In 2020, only 3.6% of the world’s population lived outside their country of birth. This has already led to a lot of anti-migrant rhetoric and policies.
Imagine when 33% of humanity have to migrate.
And we haven't even mentioned the migration of animals, insects, and arachnids, and how that could lead to more deadly disease outbreaks and global pandemics.
https://www.propublica.org/article/climate-crisis-niche-migration-environment-population