Bill Nye The Science Guy on The Atmosphere

Only a minute and a half long, this video discusses how air acts as an insulator and why air higher in the atmosphere is colder than it is down closer to Earth's surface. He defines the lapse rate and shows how to calculate it. Because of the computation involved, this would be most appropriate for your middle school earth science class. Make sure to follow the video with a discussion of how the density of air also contributes to the temperature differences.