One of the comments that I often hear from those who are skeptical about climate change is the comment that in the 1970s scientists were talking about global cooling. In particular they reference a couple of articles in Time and Newsweek which discussed recent cooling in the atmosphere and what it might mean for future climate. This week Slate published an interview with the author of the Newsweek article discussing the original article and how his views have changed since then. The interview contains some good information about how climate science has changed over time which you might find useful in discussing trends in climate over time and projections for future climate. You can read it here.
Scientific American also produced a good story on this topic (link).