> most of the time, they're optimistic.

Evidence? Has anyone collated predictions over time and compared them with outcomes to date?

I can remember a number of specific predictions (e.g. that snow would be unknown in most of the UK by the early 2000s) that were pessimistic. Of course, I recall those because they got a lot of media attention at the time and the media reporting is biased to the most extreme predictions so its not a fair sample.