|MadSci Network: Earth Sciences|
As you get to higher and higher places on the Earth, the temperature drops at a predictable rate. This change of temperature with height is called the lapse rate, and equals 1.05 degrees C per 100 metres. From there, it's just basic math. 1000 ft = 304.8 metres, which means means a temperature drop of 3.2 degrees C or 5.8 degrees F per 1000 ft.
Try the links in the MadSci Library for more information on Earth Sciences.