Uncertainties in the space-based measurements of CO2 columns due to scattering in the Earth's atmosphere

During the next decade satellites may be expected to provide a promising new source of CO2 data. However, in order for the column-integrated CO2 measurements to be useful for sources/sinks inversions, the requirements on these measurements are very demanding. In this paper we therefore quantify the largest error source for such CO2 measurements in the near-infrared wavelength range (∼1.6μm), namely the effect of aerosols and thin cirrus clouds in the atmosphere. The errors are provided for the most common used observation geometries, nadir observations over land and sunglint observations over the ocean. It is estimated that for dust aerosols the aerosol optical thickness must be known within ±0.05 for errors below ±0.5% in the CO2 total column. For other aerosol types the requirements are less strict (e.g. ±0.15 for sulfate aerosols). In the case of thin cirrus clouds over land the cirrus optical thickness must be known to ±0.05 over land surfaces and ±0.015 for sunglint observations over the ocean in case of moderate windspeed.