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Climate change is arguably the greatest environmental challenge facing us in the twenty-first century. The consequences of a warming climate are far-reaching, potentially affecting fresh water resources, global food production and sea level. Threatening impacts on the natural environment and life on Earth for generations to come, climate change is high on political, strategic and economic agendas worldwide.

The United Nations Framework Convention on Climate Change (UNFCCC) provides the centrepiece for multilateral action to combat climate change and its impacts on humanity and ecosystems. The objective of the UNFCCC is to “stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”. The UNFCCC sets out a framework and a process for agreeing to specific actions over time—a starting point for further action in the future. It establishes a framework of general principles and institutions, and sets up a process through which governments meet regularly to discuss climate change action.

In order to make decisions on climate change mitigation and adaptation, the UNFCCC requires a systematic monitoring of the global climate system.

Systematic international coordination of weather and climate observations began around the middle of the 19th century and advanced rapidly in the 1960s and 1970s as the advent of digital computers and EO satellites inspired the establishment of the operational World Weather Watch and the Global Atmospheric Research Programme. The great step forward came in the 1980s with the realisation that understanding and predicting climate would require the involvement of a much wider set of scientific communities and comprehensive observation of the entire atmosphere-ocean-land climate system. 

Improved understanding of the Earth system – its weather, climate, oceans, land, geology, natural resources, ecosystems and natural and human-induced hazards – is essential if the international climate community are to better predict, adapt and mitigate the expected global changes and their impacts on human civilisation.

Scientists concerned with climate variability and change have, from the very beginning, recognised the importance of observations to the understanding of the atmosphere and the application of atmospheric science to human affairs. Without accurate, high-quality observations on all time and space scales, climate science and services could make only limited progress.

The Global Climate Observing System (GCOS), was formally established in 1992 by the World Meteorological Organization (WMO), Intergovernmental Oceanographic Commission (IOC), United Nations Environment Programme (UNEP), and International Council for Science (ICSU), as an international, interagency interdisciplinary framework for meeting the full range of national and international needs for climate observations. To meet the need for a systematic observation of climate, the GCOS programme developed the concept of the Essential Climate Variable (ECV).

An ECV is a physical, chemical or biological variable or a group of linked variables that critically contributes to the characterisation of Earth’s climate. ECVs are not a select group of stand-alone variables. Rather they are part of a wider concept and are identified based on the following criteria:

Relevance: the variable is critical for characterising the climate system and its changes; Feasibility: observing or deriving the variable on a global scale is technically feasible using proven, scientifically understood methods; Cost effectiveness: generating and archiving data on the variable is affordable, mainly relying on coordinated observing systems using proven technology, taking advantage where possible of historical datasets.

Science and policy circles have widely endorsed the ECV concept. The parties to the UNFCCC acknowledged the need to act upon the plans for implementation. Guidelines for reporting on national programmes contributing to global climate observation are structured along the ECVs. In its planning of global observation for weather, water and climate applications, WMO addresses the ECVs and recognizes GCOS assessment and planning documents as statements of guidance.

The climate data records of observation associated with the Essential Climate Variables, the Climate Data Records (CDRs), provide the empirical evidence needed to understand and predict the evolution of climate, to guide mitigation and adaptation measures, to assess risks and enable attribution of climatic events to underlying causes and to underpin climate services.​


GCOS is progressing the systematic definition of climate information needs in support of the UNFCCC, while Committee on Earth Observation Satellites (CEOS) and Coordination Group for Meteorological Satellites (CGMS), in the form of the Joint CEOS/CGMS Working Group on Climate (WGClimate), is coordinating the planning of the satellite contribution to fulfil them.

Climate Data Records (CDRs) for Essential Climate Variables are generally derived from a combination of satellite and in-situ observations, with satellite observations making a significant contribution for a majority of ECVs. Of the 50 ECVs identified by GCOS, more than half have a major contribution from EO satellite measurements, with several exclusively derived from EO satellite measurements. The capabilities of Earth Observation satellites in support of climate information needs reflects their unique abilities and benefits –

Wide area observation capability: a single instrument on a polar orbiting satellite can observe the entire Earth on a daily basis, while instruments on geostationary satellites continuously monitor the diurnal cycle of the disk of Earth below them; Together the polar and geostationary environmental satellites maintain a constant watch on the entire globe;

Non-intrusive observations allowing collection of data to take place without compromising national sovereignty;  Uniformity that enables the same sensor to be used at many different places in the world; Rapid measurement capability, allowing sensors to be targeted at any point on Earth, including remote and inhospitable areas, enabling monitoring of deforestation in vast tropical forests and tracking ice loss in the polar regions year-round; Continuity, with single sensors or series of sensors providing long time series of data suitable for climate studies.

To respond to this UNFCCC and GCOS need for climate data, the European Space Agency (ESA) has undertaken the Climate Change Initiative programme. The objective of the Climate Change Initiative is to realize the full potential of the long-term global Earth Observation archives that ESA together with its Member states have established over the last thirty years, as a significant and timely contribution to the ECV databases required by UNFCCC. It ensures that full capital is derived from ongoing and planned ESA missions, including ERS, Envisat, the Earth Explorer missions, relevant ESA-managed archives of Third-Party Mission data and the Sentinel constellation.

The programme undertakes the activities necessary to meet its objective of supporting the UNFCCC through the GCOS defined ECVs. This includes the periodic processing of the EO data sets applying the most up-to-date algorithms, plus development of improved algorithms for the ECV production from emerging data sources consistent with the long-term record. Further detail on the association between the CCI programme and GCOS ECVs is available.

The Climate Change Initiative comprises fourteen parallel projects geared to ECV data production, plus a dedicated climate modeling user project for assessment of the products, a portal providing all products under one roof, a toolbox to facilitate the combining and analysis of the products, and a visualization tool supporting outreach.