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Frequently Asked Questions

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Over the last decade, the Global Climate Observing System (GCOS), in support of the UNFCCC, have put together a set of requirements for satellite data to meet the needs of the climate change community. These are broken down into key parameters of the Earth system, or 'Essential Climate Variables' (ECVs) as they are known. The specifications given by GCOS for each ECV data product are designed to provide information to characterise the state of the global climate system and enable long-term climate monitoring. 

In 2010 50 ECVs were defined by GCOS, with are required to support the work of the UNFCCC and the IPCC. These are described in the table below. All ECVs are technically and economically feasible for systematic observation. It is these variables for which international exchange is required for both current and historical observations.

Domain GCOS Essential Climate Variables


(over land, sea and ice)

Surface: Air temperature, Wind speed and direction, Water vapour, Pressure, Precipitation, Surface radiation budget
Upper-Air: Temperature, Wind speed and direction, Water vapour, Cloud properties, Earth radiation budget (including solar irradiance)
Composition: Carbon dioxide, Methane, and other long-lived greenhouse gases, Ozone and Aerosol, supported by their precursors
Oceanic Surface: Sea-surface temperature, Sea-surface salinity, Sea level, Sea state, Sea ice, Surface current, Ocean colour, Carbon dioxide partial pressure, Ocean acidity, Phytoplankton
Sub-Surface: Temperature, Salinity, Current, Nutrients, Carbon dioxide partial pressure, Ocean acidity, Oxygen, Tracers
Terrestrial River discharge, Water use, Groundwater, Lakes, Snow cover, Glaciers and ice caps, Ice sheets, Permafrost, Albedo, Land cover (including vegetation type), Fraction of absorbed photosynthetically active radiation (FAPAR), Leaf area index (LAI), Above-ground biomass, Soil carbon, Fire disturbance, Soil moisture.



The European Space Agency (ESA) Climate Change Initiative (CCI), is a programme whose aim is to provide stable, long-term, satellite-based ECV data products for climate modellers and researchers. This can be achieved by realising the full potential of the long-term Earth Observation (EO) archives that ESA, together with its member states, has established over the last 30 years, as a significant and timely contributions to the ECV databases required by United Nations Framework Convention on Climate Change (UNFCCC). 

The ECVs will be derived from multiple satellite data sets (not just ESA but all sources via international collaboration) and include specific information on the errors and uncertainties of the data set. Comprehensive information will also be provided on calibration and validation, long term algorithm maintenance, data curation and reprocessing. The Climate Change Initiative will bring together European expertise covering the full range of scientific, technical and development specialisations available within the European Earth Observation community, and will establish lasting and transparent access for global climate scientific and operational communities to its results.  

The €75m CCI programme, will run from 2009 to 2016 and consists of three stages: requirement analysis, algorithm development and prototype ECV building; ECV production and system development; and user analysis and feedback. Within the programme ECV have been generated for all three domains, atmospheric, oceanic and terrestrial.  

An extension to the CCI programme, called CCI+, is planned.


In the CCI Open Data Portal we have data products from the Climate Change Initiative Essential Climate Variables (ECVs), as well as links to further information and documentation.

For each ECV we hold different processing levels and products, so please have a look at the catalogue or dashboard to search the data holdings. Please note that the catalogue and dashboard are both still in development and will be released in the coming months.


The data can be downloaded by FTP, HTTP, (other protocols) and are fully open, no registration required. If you have problems downloading the data, please contact the CCI Open Data Portal Helpdesk.


Each individual CCI project website describes in detail the nature and goals about each project. This includes access to the various project documents, presentations as well as access to the generated ECV datasets. These can be accessed via the Top Menu at the top of this page.


The figure below identifies the 5 distinct tasks within the CCI ECV projects and the deliverables associated with each.

The evolution of the ECV datasets, as envisaged initially in Phase 1, was linear, going from user consultation, algorithm selection, and prototype development to product generation and validation, after which it was considered that the system and products would be ready for being made operational. 
However, for Phase 2, a cyclic approach has been adopted, which has led to an agile and versatile system, able to respond to new developments in the field, and capable of updating the products in response, such that the users will continue to receive the best products possible.

Each of the CCI ECV projects carry out one or more Round Robin exercise as part of their algorithm selection exercise.  The exercise involves both the project team and external participants, with the aim of undertaking an objective comparison of the available algorithms and selecting the most appropriate. The Round Robin exercise proceeds as follows:

  • a data package containing satellite data, in situ data, and auxiliary information is distributed to the involved parties
  • participants apply their algorithms to these data 
  • a further set of data is distributed -- identical in format to the previous data package, but without any in situ observations – which is the selection subset
  • participants apply their final algorithms to the selection subset and submit the results to the CCI team
  • objective metrics are calculated for all submitted algorithms, which are then compared and an algorithm selected for implementation in the CCI project


  • The Algorithm Theoretical Baseline Document (ATBD) records the mathematical description of the algorithms to be used in the generation of data products.
  • The Climate Assessment Report (CAR) provides:
    • Feedback from the users on the delivered ECV data products with respect to the behaviour of the time series of ECV data on global and regional scales,
    • A comparison of the output of the CCI ECV project against outputs from other related projects
  • For the Comprehensive Error Characterisation Report (CECR), please see the UCR.
  • The purpose of the Data Access Requirements Document (DARD) is to identify, in detail, all the data required as input to the project. This includes satellite, in-situ and ancillary data, both ongoing and historical, and specifies the appropriate stage when the data is required. The document is updated as needed to reflect changes in data availability or project requirements.
  • The Product Specification Document (PSD) synthesises recommendations from the URD of the CCI ECV project into a detailed set of product specifications that respond to, and are continuously assessed against, the needs.  It is structured according to product types, product formats including metadata, resolution (temporal and spatial, grid format and projection), quality indicators (e.g. long term stability) and error budgeting.
  • The Product User Guide (PUG) describes to a user the instructions required on how to use the particular CCI ECV data products generated by each of the projects.  The contents of the PUGs will generally include subjects such as:
    • an overview of the project
    • a guide to getting started with the data
    • a description of the features of each of the products
    • detailed description of the data files
    • descriptions of the tools that can be used with the data
    • worked examples on how to use the data
    • a dictionary of acronyms, abbreviations and jargon that may be encountered;
    • list of references
  • The Product Validation and Inter-comparison Report (PVIR) provides a description of the assessments used to validate the products generated by each of the CCI ECV teams.
  • The System Specification Document (SSD) describes the configuration and implementation of the system used to process the CCI ECV data products.
  • The System Verification Report (SVR) gives a description of all activities executed to validate to the correctness of the production system against the prototype system. The tests described in the report are made to verify, as far as possible, that future datasets produces by the production system will be identical to the products generated by the prototype system.
  • The Uncertainty Characterisation Report (UCR) documents the best current understanding of uncertainties (i.e., components of error distributions) in the each CCI ECV team’s observations and products.  
  • The User Requirement Document (URD) specifies the requirements for the ECV products from the user’s point of view in terms of product characterisation. The document:
    • Provides an overview of the functionality of the products that the end-user expects to obtain from each of the CCI projects
    • Provides a repository for all the requirements that will allow the end-user to exploit the products to be offered by each CCI project

There is a Product User Guide (PUG) for each variable, and more details can be found on the project websites. Links to further information are also provided via the ECV Dashboard. You can also email the helpdesk who will forward your question to the appropriate experts/data producers. 


If you use the data in a presentation or publication, please acknowledge the ESA Climate Change Initiative, and the data producer. Detailed instructions on how to do this can be found in the terms and conditions files alongside the data, but an example is given below:

AuthorName1, AuthorName2 (<year>): ESA <ECV-name> Climate Change Initiative (ESA <ECV short name> CCI) data: <Product name and Version number> via Centre for Environmental Data Analysis, Date of citation