The problem isn't really that hard, we need to have vast far reaching austerity measures be put into place immediately or the human race AND human civilization will cease to exist.
People that make arguments like yours beg the question as to economic progress and standards of living. Standards of living should drop overall, but should normalize across the population. A smooth transition is not possible.
AFAIK the extreme, apocalyptic statements you are making are not supported by the science such as the IPCC. 3-4 degrees C of warming by 2100 will not make the human race or civilization cease to exist. There are also technological options available to us to cool the planet such as seeding the upper atmosphere with dust, which we have not yet used and could provide some additional time to switch to sustainable energy production means.
In any case, a non-smooth transition is not possible right now. Look at France which was paralyzed by “yellow vest” protests for a fuel tax increase until it was rolled back - the needed carbon taxes are far higher than that small tax increase. Right now the best scenario is to continue R&D and target promotion of sustainable energy, not attempt to reduce people’s standard of living which a democratic society will refuse to accept.
AFAIK the extreme, apocalyptic statements you are making are not supported by the science such as the IPCC.
Other people here are asserting that an abrupt and urgent transition away from fossil fuels 'will crash the economy and kill off most of the population' (which I take to mean >50%) without offering any citations for that claim whatsoever.
considering modern society relies on Diesel trucks and fuel oil-burning ships to feed itself, those numbers don’t seem too crazy. If we stopped using fossil fuels tomorrow we’d have mass starvation everywhere within weeks.
So I guess it depends on what you mean by abrupt. I think we could certainly do something like add a $2/gallon tax on gas and diesel fuel without that happening, and it would reduce driving and emissions, but I would see the politicians who passed that law getting voted out at the next election as the people refuse to have their current standard of living lowered.
The year 2500? Who knows what technologies we might have available by then (e.g. fusion power enabling cheap energy to the point where we can do carbon capture and reverse warming).
What we are already seeing is that we are trending away from a baseline scenario by electrifying transport, energy generation and energy storage. And it’s probably harder to predict politics than the climate but right now I only see that trend continuing. There are some unfortunate anti-nuclear steps being taken but eventually enough solar and wind will get online to replace them. Emissions in the USA have trended down thanks to fracking and coal being wiped out.
Sea levels will rise but new land in the arctic will open up for human habitation and agriculture. Wars and migration may certainly happen but we’ve had plenty of that in the last 200 years without the end of civilization.
Obviously most people and governments aren't going to agree to voluntarily lower living standards, regardless of the consequences. So we need to focus on what's actually achievable.
People that make arguments like yours beg the question as to economic progress and standards of living. Standards of living should drop overall, but should normalize across the population. A smooth transition is not possible.