Almost 3000 non-science major undergraduates at the University of Chicago have taken PHSC13400, Global Warming: Understanding the Forecast, since Ray Pierrehumbert and I (David Archer) first developed it back in 1995.  The class is now available online,  Open Climate 101. The course is free, and one can obtain a certificate after completion of the course if one obtains a sufficiently high score on an online examination.