Satellite-based estimates of radiative forcing of long-lived halogenated gases from spectral observations

While the atmospheric concentrations of ozone-depleting chlorofluorocarbons (CFCs) are gradually declining following regulatory measures, the levels of other halogenated compounds, such as hydrochlorofluorocarbons (HCFCs) and sulfur hexafluoride (SF₆), continue to rise or are only just starting to stabilize. These halogenated substances are potent greenhouse gases. Their radiative efficiency, which quantifies, along with their lifetime, their impact on the climate, has until now only been estimated indirectly by means of models. Here, we report the clear-sky instantaneous radiative efficiencies of CFC-11, CFC-12, SF₆, HCFC-22, and HFC-134a estimated directly from an observational dataset. This is achieved by combining trends observed in 15 years (2008-2022) of spectrally resolved infrared radiance fluxes from the Infrared Atmospheric Sounding Interferometer on Metop satellites, with concentrations measured from ground and space. Comparisons with literature-reported values generally confirm previous model estimates, with some notable differences. The most significant discrepancies are for CFC-11 and SF₆, with our estimates being 27% lower, but nevertheless, within the bounds of the uncertainty estimates.