"the gases that don't let the heat out'!! Hardly. CO2 is IR reactive, meaning it absorbs AND EMITS heat energy. It absorbs from a warmer source (the surface) and emits to a cooler source (the higher atmosphere). It cannot trap it but transports it upwards.  However, even that pales into insignificance compared to the conductive and convective cooling that transports most of the heat upwards towards space, where IR reactive gases such as CO2 radiate it out to space, all of which keeps our planet cool enough to habitate