© Adobe Stock / Andrei Armiagov
As the global community marks World Metrology Day 2026, ECMWF is underlining the critical role of measurement science in shaping effective environment and climate policies and in building trust in the decisions designed to make our world better, including those that may be taken at the COP31 climate summit later this year.
This year’s theme, “Metrology: Building Trust in Policy Making”, reflects a growing recognition that robust, transparent and internationally consistent measurements are essential for evidence-based decisions. At a time when countries are striving to translate climate commitments into concrete action, the ability to measure the evolution of atmospheric pollutants and greenhouse gas concentrations accurately, and to verify progress independently is becoming central to global policy discussions.
Laurence Rouil, Director of the Copernicus Atmosphere Monitoring Service at ECMWF, comments: “In the past decade, Europe’s drop in nitrogen dioxide (NO2) and particulate pollution (PM) proves that when you measure properly, you can manage effectively and deliver real change for society.
"At ECMWF, through the Copernicus Atmosphere monitoring Service, we are able not only to track these changes but to demonstrate their impact. As we approach COP31, this same tracking capability allows us to measure progress, or non-progress with confidence. Strengthening this measurement foundation will be key to turning commitments into demonstrable results."
Atmospheric monitoring
Through the Copernicus Atmosphere Monitoring Service, implemented by ECMWF on behalf of the European Commission, Europe is investing in the sustainable uptake of measurement infrastructures needed to support these efforts. The service delivers consistent and quality-controlled information on atmospheric composition, including air pollutants and greenhouse gases, derived from a unique combination of satellite observations, in situ measurements and advanced modelling.
This measurement capability is increasingly being extended from monitoring concentrations to estimating emissions themselves. Work under way includes the development of the CO2 Monitoring and Verification Support capacity (CO2MVS), which will combine Earth observations and modelling to provide independent assessments of greenhouse gas emissions and their evolution over time, supporting monitoring, reporting and verification processes.
Complementary tools, such as the Methane Hotspot Explorer, shows how observation-based approaches can identify major emission sources globally, helping to target mitigation efforts more effectively.
As negotiations move toward COP31, where countries will be expected to demonstrate tangible progress on emissions reduction, the importance of reliable measurement is only increasing.
By ensuring that data are traceable, transparent and accompanied by quantified uncertainties, ECMWF’s activities contribute to the foundation of trust needed not only in scientific information, but in the policies and international agreements that depend on it.
In this context, World Metrology Day serves as a timely reminder: effective environment and climate action starts with the ability to measure it.
Going further
ECMWF receives 800 million observations daily, from satellites but also from sources such as aircraft, ships, sea buoys and many other Earth-based measurement stations, all of which rely on accurate measurements.
These observations provide information on, for example, the Earth’s atmosphere, pressure, moisture, temperature and wind, but also the chemical composition of the atmosphere. Scientists then select around 60 million quality-controlled observations which are then fed into ECMWF's Integrated Forecasting System (IFS), its global weather system used to produce weather and atmospheric forecasts.
These initial conditions, combined with historical datasets, are used to create forecasts that are applied worldwide, not only for weather prediction but also for atmospheric forecasts providing air quality intelligence.
The forecasts are used by our Member and Co-operating States and their meteorological and hydrological services, as well as by air quality experts responsible for implementing European Union (EU) regulations, and they enable policymakers to make decisions about mitigating measures. The availability of accurate measurements is crucial for producing high-quality analyses to initialise forecasts and to evaluate their performance.
One example of data underpinning policy that has led to a significant positive change is through the European Union’s (EU) Ambient Air Quality Directive.
Air quality in Europe has improved steadily over recent decades and the EU is on track to cut the health impacts of air pollution by more than 55 percent by 2030 compared to 2005. This progress is supported by legislation that has set new targets for reducing exposure to air pollutants such as PM2.5 and PM10, NO2 and ozone (O3), which originate from traffic, industry, residential heating, agriculture and from natural sources such as Saharan dusts or wildfires. Air pollution is still responsible for hundreds of thousands of premature deaths as well as biodiversity loss in Europe, but the improvements so far show that policy, underpinned by accurate data, is making a difference.
Together with experts from national agencies, environment institutes, space agencies, and research laboratories, ECMWF provides some of the world’s most comprehensive insights into the composition of the atmosphere. These resources are available freely online.