Essential Climate Variables (ECV) have been defined by the Global Climate Observing System (GCOS) since the late 1990s. Over the years, the list of ECV has evolved significantly to reflect advancements in both observing systems and the complexity of climate monitoring.

GCOS currently defines 55 ECVs in the atmosphere, ocean and terrestrial domains (see below or refer to our glossary)

ECV rationalization

In 2024, the GCOS Steering Committee established an ECV Rationalization Task Team to conduct a comprehensive review of ECVs and their governance, with a goal to finalize a revised set of ECVs by 2028. Recently, the Task Team released a draft revision of the ECVs, which, after internal consultation, have been subject to an open, formal review.

The goal of the review is to settle on a new list of ECVs that reflect the set of observations that are needed to monitor our changing climate.

The review was guided by the following questions:

• Are all 55 current ECVs still relevant?
• Is the current categorization of ECVs optimal?
• Are the ECVs consistent across the different domains?
• Are the processes for adding or changing ECVs transparent and coherent?

More information about ECV rationalization is available on GCOS website: https://gcos.wmo.int/site/global-climate-observing-system-gcos/essential-climate-variables/ecv-rationalization

ObsSea4Clim contribution

One of the key objectives of ObsSea4Clim is refining the current global EOV/ECVs framework to address regional and national climate information needs. Therefore, as a project we provided a contribution to the public ECV review process.

In order to provide most comprehensive inputs, ObsSea4Clim conducted internal meetings to coordinate inputs from different partners and tasks across the project. In the meetings, each proposed ECV was discussed.

We look forward to seeing the results of the review process, and we will continue to support GCOS in this important task.

More information about the public review process is available on WMO website: https://wmo.int/media/magazine-article/call-review-of-essential-climate-variable