The Climate Models have errors. Those Errors increase as you go farther out in the future. When you are 100 years in the future - the Error Cone is so large that
Any changes we make today, up to outlawing private cars and stopping commercial flight completely - will be obscured by that error.
Nothing we do will even be noticeable.
The very idea that we can model something as complex as climate is an error in itself.
It’s not just something we are currently incapable of, it’s something that we already know is mathematically impossible.