If you double the mass of Earths atmosphere with more N0, why would that slow the radiant energy loss from the surface. Adding more non-GHG will impact the radiation by raising the radiative Top of Atmosphere (ToA). Doubling the bulk of the atmosphere (even ussing non-GHGs like N0) will raise the GHG molecules as well, so they will be radiating to space from a higher altitude. But since higher altitudes tend to be cooler due to the lapse rate, the GHGs at the new, higher, cooler ToA will radiate LESS to space. This will create a back up of energy all the way down to the surface. Ultimately, the surface will get warmer (and actually INCREASE the radiant energy to space through the atmospheric window to compensate for the reduced radiant energy from the TOA). (yes, there are lots of feedbacks that will change a few of the details, but that is the basic argument.)