Researchers investigating global climate change need measurements of greenhouse gases with extreme precision and accuracy to enable the development and benchmarking of better climate models. Existing atmospheric monitors based on non-dispersive infrared (NDIR) sensors have known problems – they are non-linear, sensitive to water vapor concentration, and susceptible to drift. Many cannot easily be simultaneously calibrated across different sites to the level of accuracy required for use in atmospheric studies. We present results from field trials by Pennsylvania State University and the National Oceanographic and Atmospheric Administration (NOAA) of a newly available analyzer, based on cavity ring-down spectroscopy (CRDS), capable of measuring the concentrations of carbon dioxide (CO₂) and water vapor (H₂O). In addition, we present data from a new analyzer which measures CO₂, methane (CH₄), and H₂O.