A measurement of the altitude variation of greenhouse radiation from CFC-12

Abstract

Here we report measurements that provide new experimental evidence to support climate model predictions of the greenhouse effect. We demonstrate that emission of chlorofluorocarbons (CFC) into the atmosphere by anthropogenic usage has modified the long-wave radiation budget of the atmosphere by ∼0.1%. The 10.8-μm band of CFC-12 is situated in the thermal window of the atmosphere and hence has a powerful greenhouse effect. Measure-ments of the downward long-wave infrared flux in this band have been made with a filter spectrometer, covering the spectral range 9–14 μm, as a function of height over an altitude range 5–25 km. The balloon ascent took place on 19 May 1985 from Palestine, Texas at 31° N under clear sky conditions. The observed radiance profile is consistent with a model flux calculation using the observed temperature profile. The downward flux measured at the tropo-pause was 0.008 W m⁻²; this will be potentially valuable for com-parison with unpublished climate model fluxes for mid-latitudes in summer. The measured downward greenhouse flux at 5 km was 0.05 Wm⁻², which is consistent with published climate model values for the radiation change at the surface, after accounting for the pressure difference.