1. Lifetime: CFCs tend to have long lifetimes. For example, CFC-12 can spend 100 years in the troposphere before diffusing higher up into the stratosphere and affecting the ozone layer.
2. Concentration: Compared to other greenhouse gases such as carbon dioxide, CFCs are not present in very high concentrations.
3. Region of IR radiation absorbance and how strongly the gas absorbs: CFC molecules absorption peaks are within the range of Earth's IR emission spectrum (you can see this by selecting the spectrum of CFC-12 and 'Earth's Scaled Emission Spectra' in the IR Windows Learning Tool). Also, the absorption peaks are generally quite intense, so the CFC molecules strongly absorb IR radiation. Therefore, even low concentrations of CFCs may absorb significant amounts of IR radiation emitted from Earth. Finally, CFC molecules absorb in a different region of the IR spectrum than carbon dioxide and water vapour – so they trap IR radiation that would otherwise escape into space and cool our planet.

Consider the three factors that affect the significance of a greenhouse gas:

1. The super greenhouse gas would have a very high concentration in the atmosphere.
2. The gas would absorb IR radiation very strongly and directly in the peak of Earth's emission spectrum, at about 500 cm^-1. It would not overlap very much with the absorption peaks for the most important greenhouse gases, water vapour and carbon dioxide.
3. The gas would be extremely unreactive and, consequently, would have a very long atmospheric lifetime.