GCOS ECV Rationalization
The Global Climate Observing System (GCOS) Essential Climate Variables (ECVs) Public Review: A chance to be involved

The Global Climate Observing System (GCOS) is an international initiative co-sponsored by the WMO, IOC, UNEP, and ISC. Its purpose is to ensure that measurements of critical climate variables are compiled, sustained, coordinated, and enhanced. One of GCOS's primary responsibilities is the definition of Essential Climate Variables (ECVs), which represent a minimum set of observed variables that are needed to monitor the Earth's changing climate. ECVs span across three panels/domains: the ocean, land, and atmosphere. These variables have been fundamental for evaluating the effectiveness of climate observing systems, guiding research and policy investments, and establishing standards and practices for monitoring and data management. They are also a communication tool which helps mobilizing climate observing communities. An ECV may be described by one or more ECV quantities. And ECV quantity is a property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference. ECV quantities were called "ECV products" in the past

ECVs have been selected and developed as the result of a thoughtful analysis based on three guiding principles:
  1. An ECV must reflect a critical and sustainable global observation necessary to monitor, understand, or predict climate change, with scientifically established methods for measurement.
  2. The data related to the ECV must be archived, curated, and made accessible, leveraging existing historical datasets where applicable.
  3. The measurable quantity/ies related to the ECV should form the baseline set of data required to describe the Earth's climate and its evolution.
When GCOS first developed the ECVs in the late 1990s, their list of essential variables was relatively small. Over time, the list has evolved to reflect advancements in both observing systems and the complexity of climate monitoring and process understanding. As part of an ongoing review, key questions have emerged:
  • 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?

In 2024, the GCOS Steering Committee established a Task Team to conduct a comprehensive review of ECVs and their governance, with a goal to finalize a revised set of ECVs by 2028. After a draft revision of the ECVs was proposed by the Task Team, key stakeholders were then interviewed in Q3 2024 to gather initial feedback. Now, an updated set of ECVs has been developed that are undergoing an open, formal review. This review started in December 2024 and it is planned to finish at the end of 2025. However, the new ECV list will only enter into force when the new GCOS Implementation Plan is published (in 2028).

It is crucial that the new set of ECVs reflect the essential set of observations that are needed to monitor our changing climate. As GCOS moves forward through this process, your input is invaluable to ensuring that the process is robust and well-informed. Anyone is welcome to contribute to this review. We encourage you to provide feedback during this review. We have included some prompt questions and answers to those would be greatly appreciated! For further information and detailed instructions on how to provide feedback, please refer to the FAQ section and review guidelines.