Metrology for SI traceable climate observations

Over half of the 55 Essential Climate Variables, used to predict how the Earth’s climate is evolving, has a space-based contribution. The MetEOC series of projects: • MetEOC (2011-2014) improved NMI calibration facilities, including ones used to calibrate instruments in the field. • MetEOC-2 (2014–2017) improved performance of an originally lab-based cryogenic solar radiometer to enable improvements of measurements of incoming solar radiation by a factor of 10 and developed standards and instrumentation for the characterisation of large areas of ocean, vegetation and desert, used to confirm satellite-borne instrumentation performance. • MetEOC-3 (2017-2021) integrated tuneable laser methods into calibration facilities such as STAR, to allow enhanced calibrations of spectroscopic instruments, for example, to retrieve localised measurements of CO₂. • MetEOC-4 (2020-2023) further improved the accuracy of calibration facilities, developing new instrumentation and standards to allow more comparable data on sky radiance from ground-based networks. These results will provide trustworthy evidence to policy makers and help timely and measured mitigation strategies to be implemented.