  Atmospheric CO$_2$ concentrations are being closely monitored by remote
sensing experiments which rely on knowing line intensities with an uncertainty
of 0.5\%\ or better. Most available laboratory measurements have uncertainties
much larger than this. We report a joint experimental and theoretical study
providing rotation-vibration line intensities with the required accuracy. The
{\it ab initio} calculations are extendible to all atmospherically important
bands of CO$_2$ and to its isotologues. As such they will form the basis for
detailed CO$_2$ spectroscopic line lists for future studies.
