Thermodynamic and metrological issues in environmental measurements.

Environmental measurements represent a phenomenal societal and scientific challenge of ever-growing importance in the light of the ongoing and future climate variability. Thermal quantities (air, sea, snow and soil temperature, humidity, permafrost depth) are key among the Essential Climate Variables (ECVs) as defined by the WMO Global Climate Observing System in these areas. In order to accurately capture climatic trends and enable early detection, metrological rigor in terms of sensor calibration and uncertainty budget evaluation are of paramount importance. For this reason, the metrology and meteo/climatic communities have started a decade-long ongoing cooperation through the mutual recognition accords between the WMO and BIPM, which led to the exchange of representatives in WGs, the co-hosting of a series of joint workshops ("Metrology for Climate Action"), and a general strict cooperation, through the development of new measurement techniques and instruments; the understanding of uncertainty components both for laboratory calibration and for field conditions; the accurate evaluation of quantities of influence; and the development guidelines, best practices and recommendations.