If you can’t accurately model the climate next month, then you certainly can’t model it for next year. If you can’t model it next year, you certainly can’t model it for 50 years.
The whole point of climate models is to run them iteratively in order to compound feedbacks – which means that errors increase exponentially. People claiming that errors average out have no idea what they are talking about.
If you drive faster and faster in the wrong direction, you get further and further away from your destination.