The effect of CO2 variability on the retrieval of atmospheric temperatures

The effect of spatial variability of the atmospheric CO2 distribution on temperature and water vapor retrievals from high spectral resolution observations of infrared emission is estimated by performing 4 different retrieval experiments. Using a global mean CO2 value, as currently routinely used, introduces errors in the retrieved temperature profile of up to 0.85 K compared to a retrieval in which the CO2 profile is known exactly. Including CO2 in the retrieval vector reduces these errors to 0.3 K. A more practical alternative, especially for data assimilation, is to use a monthly mean zonal mean CO2 value, which produces errors of up to 0.35 K in the temperature profile.