A National Research Council committee is conducting a study on how well greenhouse gas emissions can be measured for treaty monitoring and verification. The committee's analysis suggests that NASA's Orbiting Carbon Observatory (OCO), which failed on launch in February 2009, would have provided proof of concept for spaceborne technologies to monitor greenhouse gas emissions, as well as baseline emissions data. This letter focuses on the capabilities of an OCO and currently deployed satellites that measure atmospheric carbon dioxide (CO2) and their potential role in monitoring and verifying a greenhouse gas treaty.