I can see where he is coming from, but what is his definition of a non-scientist? Does he mean someone with no scientific understanding at all, or does he mean someone who is not a climate scientist? I could go further than the writer and say that even an expert climate scientist is guessing when he makes claims about the future because the known science to make such predictions simply does not exist, as the writer himself states at the beginning when he states "no scientist really believes that complicated models with lots of variables can reliably predict the future".
Of course we make lots of decisions based on guesswork, though to make it sound more respectable we don't use that word, preferring to use "balance of probabilities", or "best estimate", etc. to give an illusion of greater knowledge. In the end if that is all we've got then we have no choice, as decisions have to be made. Even deciding to do nothing is a decision, and often it is the best decision as it is the least expensive.