Back in 2009, it was 200 million climate refugees according to this article in the NYT:

„There could be 200 million of these climate refugees by 2050, according to a new policy paper by the International Organization for Migration, depending on the degree of climate disturbances.“

Now the claim is up to 5 times that by 2050 in the space of five years, at this rate of increase, the entire world population will be ‘climate refugees’ by 2050.