Technical Note: On the Experimental Confirmation from Space of the Spectral Signature of CO₂ Growth

Abstract. We present conclusive experimental confirmation from space that the observed impact of CO₂ growth on longwave spectral radiances follows theory, both in the troposphere and stratosphere, and that these results are independent of CO₂ uncertainties. We refine the methodology used in a previous study on the direct measurement of the impact of increased atmospheric CO₂ on the spectra of Earth's longwave radiation by addressing three critical issues and as such provide a definitive experimental confirmation from space of the impact of CO₂ growth on longwave spectral radiances. In our study, we (i) use temperature profiles retrieved from microwave radiances for our analogue methodology, clearly illustrating the independence of our approach from any role that the longwave spectral radiances may play in the retrieval of the analogue temperature profiles; (ii) show that the effect of the uncertainties due to CO₂ spatial and temporal variability when estimating theoretical spectral radiances is small (often imperceptible) and has no meaningful impact on the interpretation of the results; (iii) show that the CO₂ growth spectral signature in the stratosphere can be captured by using a slight variant of the method that allows to conclusively detect the more challenging stratospheric signature. By addressing these three critical issues, refining our methodology and extending the initial study, our current results conclusively confirm a critical theoretical foundation of the science of global warming.