Climate change is arguably the greatest environmental challenge facing us in the 21st century. The consequences of a warming climate are far-reaching, affecting fresh water resources, global food production and sea levels. With worsening impacts predicted for the natural environment and society for generations to come, climate change is high on political, strategic and economic agendas worldwide.
The policy need
The United Nations Framework Convention on Climate Change (UNFCCC) is leading international efforts to combat climate change and limit global warming to well below 2 degrees Celsius above pre-industrial levels, as set out in the Paris Agreement. To achieve this objective and to make decisions on climate change mitigation and adaptation, the UNFCCC requires systematic observations of the climate system.
A global observing system
Systematic international coordination of weather and climate observations began around the middle of the 19th century and made a great step forward in the 1980s with the realisation that understanding and predicting climate would require an improved understanding of the Earth system as a whole – its weather, climate, oceans, land, geology, natural resources, ecosystems and natural and human-induced changes. Without accurate, high-quality observations at sufficient resolution in both time and space, 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).
The Climate Data Records (CDRs) of observation associated with the ECVs 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.
The Space Agencies' response
GCOS is progressing the systematic definition of climate information needs in support of the UNFCCC, while the 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) – are coordinating the planning of the satellite contribution to fulfil them.
CDRs for ECVs 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 55 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 EO 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.
The Response from ESA
To respond to this UNFCCC and GCOS need for climate data, the European Space Agency (ESA) has undertaken the Climate Change Initiative (CCI) programme. The objective of the CCI is to realise the full potential of the long-term global EO archives that ESA, together with its Member states, has established over the past 40 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.
The CCI programme comprises 27 parallel projects geared to ECV data production, plus a dedicated climate modelling user project for assessment of the products, an open data portal providing all products under one roof, a toolbox to facilitate the combining and analysis of the products, and a visualisation tool supporting outreach.