The Greenhouse Effect was simulated in a laboratory setup, consisting of a heated ground area and two chambers, one filled with air and one filled with air or CO2. While heating the gas, the temperature and IR radiation in both chambers were measured. IR radiation was produced by warming a metal plate, painted with heat-resistant, matt black paint, mounted on the rear wall. Reduced IR radiation through the front window was observed when the air in the foremost chamber was exchanged with CO2. In the rear chamber, we observed increased IR radiation due to backscatter from the front chamber. Based on Stefan Boltzmann’s law, this should noticeably increase the temperature of the air in the rear chamber, but no such increase was found. A thermopile, made to increase the sensitivity and accuracy of the temperature measurements, showed that the temperature with CO2 increased slightly, just within the uncertainty range.