Even if the oceans were utterly sterilized today, with all the atmospheric implications that go with that, it would take longer than 20 years for Sweden to no longer exist.
I'm not saying that climate change won't cause huge environmental disasters and social unrest, because it will. I'm saying that "there won't be a planet left after 20 years" is extreme pessimism and unsupported by any model backed by science, even if you read that claim generously and assume "won't be a planet left" is merely hyperbole for the collapse of Swedish society.
Many people mistakenly or vaguely conflate global civilization with "the planet". The distinction doesn't really matter much, from a policy perspective.
I can only say that you are probably right. But we don't know if the ocean ecosystem will collapse in that time, bringing down civilization.
The thing about collapse is that it happens terrifyingly fast, and is only sometimes predicted accurately.