We seem to have under estimated the speed / time scale of changes and their effects. Being told this will happen within the next century means most people will be dead and not affected, so less urgency, our me me society means that we don't consider the consequences on subsequent generations.
What appears to have happened is that these temperature rises seem to be happening far quicker than these predictions. We just had a report about the gulf stream collapsing, again this could happen by 2025 or decades ahead.
Of course, If I understand things, predictions are based on collected data, historical data and how we analyse that data, what data we put in to the model.
As we have failed to take things in to consideration or got wrong results is just siezed upom by climate deniers to question or models, (they don't have their own alternative data backed model of course).
Of course we can't input all factors, as I am guessing that has its own issues.
