The World Meteorological Organization’s Global Atmosphere Watch (WMO GAW) published new measurement guidelines for observations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) at GAW stations.
These guidelines have emerged to help address the need for increased density of long-term surface measurements of greenhouse gases. They act as best practice guidelines for setting up observatories to make high quality measurements of atmospheric concentrations of CO2, CH4 and N2O.
Published in October 2025, these guidelines represent the culmination of several years of work, with significant contributions from the ICOS Atmosphere community. Both the experiences of establishing the ICOS network in Europe and the ICOS Atmosphere Thematic Centre (ATC) station specifications were major contributors to the GAW guidelines.
A long time in the making
Establishing measurement guidelines that can be applied on a global level understandably takes time, according to Martin Steinbacher (Principal Investigator of ICOS Atmosphere station Jungfraujoch and former chair of the ICOS Atmospheric Monitoring Station Assembly) and one of the lead authors of the paper.
“I was approached by the GAW Secretariat in 2019 to contribute as I run one of GAW Quality Assurance/Science Activity Centres. At that point, previous efforts to complete a final draft had already stalled, likely due to an overcommitment of the author team,” says Martin.
“The various chapters were distributed among a lot of contributors, but at various points other work duties would again postpone things.”
Initially planned to cover only CO2 and CH4, the guidelines were expanded to include N2O during the writing process. Beyond practicalities, it also took time to reach consensus on a wide range of topics.
Martin outlines how a whole host of factors had to be considered: “There were many, many technical questions we had to consider – what is the best suited measurement technique, which calibration gas to use, which valve do you attach to the cylinder, how often you calibrate, which tubing material is most suitable for our applications, …the list goes on”
“From there we had to integrate a lot of opinions from different networks, perspectives and backgrounds while trying to be as conclusive as possible. So, as you can imagine this took quite some time!”
ICOS is the blueprint for a global network
When establishing technical guidelines for atmospheric measurements it makes sense to look at and adapt available guidelines.
“The ICOS ATC station specifications acted as one of the blueprints for these guidelines, as did the experiences of the community in establishing ICOS,” Martin explains. “Many conclusive details and discussions from Atmosphere Monitoring Station Assembly (MSA) meetings have made their way into the GAW guidelines.”
Now that they’ve been published, how do the GAW guidelines impact the work of ICOS Atmosphere stations?
Approximately one third of ICOS Atmosphere stations have been long standing contributors to the GAW network. Newer ICOS stations have likewise benefitted substantially from the accumulated expertise in both ICOS and GAW. In short, ICOS stations also adhere to these new guidelines.
The debate on standardisation
ICOS measurements are highly standardised, a decision taken when establishing the ICOS network.
“There have been discussions about the pros and cons of standardisation over the years,” Martin explains.
Standardised data ensures high observational standards and best possible compatibility, but there is an inherent risk: if all measurements are standardised and a substantial systematic flaw is detected only after several years, all data is compromised.
“To avoid this, ICOS has very stringent quality assurance and quality control protocols,” continues Martin, "since no one measurement technique is fool proof."
Globally, there are calls for the use of a range of different techniques, to allow for spotting of eventual systematic biases. This had to be also considered in the guidelines.
“When developing the GAW guidelines, trade-offs had to be made between standardisation and allowing for diversity."
While these guidelines are current state-of-the-art, technological and other developments will prompt the need to review and update the guidelines in the future.
“The guidelines will likely be reviewed in future meetings of the global greenhouse gas experts, with changes arriving as addendums,” Martin outlines.
“If the techniques advance, they will be included in future editions.”
