The NRC Decadal Survey calls for long-term climate records of high accuracy that are tested for systematic errors on-orbit, and are tied to irrefutable standards such as those maintained in the U.S. by the National Institute of Standards and Technology (NIST). The Climate Absolute Radiance And Refractivity Observatory (CLARREO) is a climate-focused mission designed to meet these goals. The foundation for CLARREO is the ability to produce irrefutable climate records through the use of exacting on-board traceability of the instrument accuracy and systematic sampling of the Earth for climate records. Spectral reflected solar and infrared radiances and Global Positioning System Radio Occultation refractivities measured by CLARREO will be used to initiate an unprecedented, high accuracy record of climate change that is tested, trusted and necessary to provide sound policy decisions. This record of direct observables will have the high accuracy and information content necessary to detect long-term climate change trends, to test and systematically improve climate predictions, and to assess and predict the impact of changes in climate forcing variables on climate change

This presentation will focus on the scientific foundation for CLARREO, a description of the science objectives and measurement requirements, initial Pre-Phase A study results, and NASA's mission implementation strategy.