@georgeob1,
I find your overuse of the word "justifiable" amusing.
You are also confusing predicting the future (which is, as you say, difficult) with predicing the past (which is not so difficult).
There is a strong scientific consensus that there is now measurable global warming. There is a just as strong scientific consensus that this global warming which has happened is caused in significant part by human activity. (I don't know if you accept either of these facts, but they are both widely accepted across the scientific community).
In my understanding... it is the predictions about what this means for the future that have uncertainty.
But... let's get back on topic.