In accordance with its Memorandum of Understanding5, GCOS prepares regular reports on the status of the global climate observing system followed by implementation plans that address issues and gaps, and new developments and user needs. These reports are 6 submitted to the WMO and UNFCCC Subsidiary Body on Science and Technology (SBSTA) . In the 2016 GCOS Implementation Plan7, endorsed by the WMO8 and UNFCCC9, the review and updating of ECV requirements is addressed by actions G10-13. Chapter 2 outlines the general process.