text: What happens to an air parcel when a CO 2 molecule absorbs an IR photon? Since the molecule can only exist in specific discrete energy states it jumps to a higher (excited) energy state. However in this process the translational energy of the CO 2 molecule does not change. The average speed of the molecules of the air parcel containing this CO 2 molecule has not increased. Since temperature is related to the root mean square speed of the molecules the temperature of the air parcel does not increase. CO 2 does not trap heat.