Global warming prediction with modtran at 70 km
your image should have been seen here!
70 km can be consider above the radiative top of the atmosphere, a natural place to seek restoration of radiative balance. But this exercise neglects the stratospheric cooling that occurs as a result of the increased emission in the strong, central region of the CO2 band. Thus the warming of the troposphere is underpredicted; the exercise at 20 km gives a result closer to (though still less than) predictions by a GCM.