A little research has revealed that the 7k number back in about 1950/60 was an educated guess - no one really knew - and the 30k number is less of a guess but still pretty uncertain. It varies with he source from 25k to 31k. There are still huge regions of the far north where even progressives will agree that we have no idea how many, if any, polar bears there are.
Just like temperatures before maybe the 1900's, it's a big guess, and that guess is tainted by the politics of the person making it. So, it's only prudent to take all Chicken Little predictions of fiery death in the future with a grain of salt. Or a face full.