Question: What’s the difference between a computer salesman and a used car salesman?

Answer: A used car salesman knows when he’s lying.

I was reminded of this old joke when reading Jim Hoggan’s book “Climate Cover-Up: The Crusade to Deny Global Warming” on the campaign to obscure what science tells us about global warming: it’s happening and we’re causing it. Hoggan tells us about the cast of characters involved in this campaign and I found myself classiying them into two
categories: those who don’t know they are lying and those that do.