If waves of tens or hundreds of millions of refugees leaving places they cannot live in any longer begin sweeping across borders, how long will it be before fascist governments, already threatening, and already winning in Turkey, Poland, Russia, Belarus, the Philippines, Brazil, Hungary, Italy, and India take over generally and initiate wars, as they do? Such wars might not go thermonuclear, but they would certainly disrupt fragile global trade networks.
As for global thermonuclear war, we could wargame likely scenarios and potential outcomes endlessly until the day it might actually happen. But anybody who tells you with certainty that one will happen in the next 20 years so there's no sense planning for the future (e.g. no sense building a power plant that will be used 20 years from now) is trying to indoctrinate you into a doomsday cult.
Nothing happening today, extrapolated out to 20 years with the most severe climate models, will be severe enough to cause the "end of the world". Anybody who's telling you we'll have total societal collapse by 2042 is out of touch with reality. The only way for things to go that badly that fast is for Earth to be hit by something big from space, but that is very unlikely to happen in any given 20 year period.
It will get worse. Billions of people will be directly affected.
Soon, they will try to make their way to countries that are still kind of functioning (because they are rich), where people that are most responsible for climate change will label them "economic migrants", and say they don't have a right to come.
So yes, there will probably be a planet, just not one that will be very pleasant for living. I don't think we have time for solutions that have failed to deliver for decades, need subsidies to be built, maintained and even shutdown, and take forever to get completed.
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.
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.
Some in the short term, more in the long term. But I challenge you to find any sane climate model that says Sweden won't be around in 20 years to use any infrastructure built today.
Using climate change as an argument against building any long-term infrastructure is insane, and is probably anti-nuclear motivated thinking. What are the odds I find such doom-saying in the discussion about a bridge being designed to last 50 years? Oh gee, no point building a bridge that lasts 20 years since we'll all be dead by then, right? Tell all the architects and construction firms to stop building apartment buildings to last more than 20 years, right? Yeah right. This extreme sort of doom-saying is reserved for discussions about infrastructure planning that is opposed by the doom-sayer for some other unstated reason.
"The planet is fine... the people are fucked"