Here's an article on it: https://www.salon.com/2015/07/10/this_is_what_its_going_to_l...
Some predictions are even more extreme: https://phys.org/news/2015-09-fossil-fuel-meter-sea.html
It's probably not the most likely outcome, but it's also definitely not "fear mongering bs", it's part of what science is discussing as possibilities.
I.e. about the "extra 20ft of risen sea"
The recent studies I've explored predict around 50-130cm by 2100. However, I have seen discussions of ~20ft by 2200 and 26ft by 2300 (https://www.theatlantic.com/science/archive/2019/01/sea-leve...), alongside more alarming figures (https://www.annualreviews.org/doi/10.1146/annurev-environ-10...).
You might be interested to read The Myth of the 1970s Global Cooling Scientific Consensus: http://nora.nerc.ac.uk/id/eprint/11584/1/2008bams2370%252E1....
Excerpt: "There was no scientific consensus in the 1970s that the Earth was headed into an imminent ice age. Indeed, the possibility of anthropogenic warming dominated the peer-reviewed literature even then."