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Case Studies
  GCOS and its Important Role in Observing the Earth’s Changing Climate  
  ESA’s Climate Change Initiative  
  Global Forest Observations for Forest Carbon Tracking  
  Tracking Human Perturbation of the Carbon Cycle  
  Indicators of Climate Change  
spacer GCOS and its Important Role in Observing the Earth’s Changing Climate

Observations are fundamental to improving the scientific understanding of climate and to delivering the vetted, timely and purposeful climate information needed to support climate mitigation and adaption decision-making. The demand for information on global climate has been increasing since the inception of the IPCC (Intergovernmental Panel on Climate Change) and the WCRP (World Climate Research Programme) nearly three decades ago. Many regions in the world are clearly impacted by changes in climate and those changes need to be managed now.

Observation and monitoring of the Earth’s changing climate is a key element of the emerging Global Framework for Climate Services and, more generally, underpins climate research, assessment of climate change and the development of policy responses.

The Global Climate Observing System (GCOS) was established in 1992 by the World Meteorological Organization (WMO), Intergovernmental Oceanographic Commission (IOC), United Nations Environment Programme (UNEP), and International Council for Science (ICSU) with a comprehensive GCOS plan agreed by mid-1995.

Since then, GCOS, working with national agencies and international organizations such as the sponsors of GCOS, has made significant progress. Routine observations have been improved to meet the exacting demands of climate records, aid provided for the deployment of critical new observing systems and assistance provided to developing countries to improve their observing networks. Significant results include:

– Defining the Atmospheric Observing Network for Climate

– Developing Ocean Observing Networks for Climate

– Facilitating the Expansion of Terrestrial Climate Networks

– Establishing Important Links to the UNFCCC

– Defining the GCOS Climate Monitoring Principles

– Producing the Adequacy and Progress Reports and Implementation Plans

spacer – Promoting the Development of Satellite Observing Systems for Climate

– Implementing a GCOS Regional Workshop Programme

GCOS introduced the widely accepted concept of ECVs and addressed the need for global coverage and timeliness of data. The GCOS Climate Monitoring Principles were adopted by the UNFCCC in 2004. The UNFCCC also emphasised the principle of free and unrestricted exchange for ECV datasets.

Essential Climate Variables (ECV)

In the 1990s, gaps in knowledge of climate and declining core observational networks in many countries led to calls for systematic observation of a limited set of critical variables. To provide guidance, the GCOS programme developed the concept of ECVs, which has since been broadly adopted in science and policy circles.

An ECV is a physical, chemical or biological variable (e.g. precipitation) or a group of linked variables (e.g. permafrost: area, depth and temperature) that together characterise the Earth’s climate. ECV datasets 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.

Observing the ECVs and generating climate datasets should be relevant, feasible and cost-effective.

GCOS, together with the WCRP, co-sponsors three climate observation panels (Atmosphere, Ocean and Terrestrial) whose role is to assess the global observing system, review the adequacy of the observing networks, identify measureable key variables (ECVs) and coordinate with other global observing systems.

In addition, the GCOS Co-operation Mechanism (GCM), which once originated from the UNFCCC and its Subsidiary Body for Scientific and Technological Advice (SBSTA) allows developed countries to contribute funds to address specific needs in climate observing networks in developing countries.
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spacer spacer Establishing Observational Systems

The largest observing system, together with operational meteorological satellites, is the World Weather Watch/ Global Observing System (WWW/GOS) of WMO. National Meteorological and Hydrological Services (NMHSs) provide the fundamental atmospheric networks. However, there is a need for a worldwide system capable of producing observations of greater accuracy and coverage and comprising additional appropriate climate variables. Among those needed are the atmospheric chemistry variables measured as part of the WMO’s Global Atmosphere Watch (GAW).

GCOS defined a subset of the WWW stations of roughly 1000 baseline surface stations that became the GCOS Surface Network (GSN), while a select set of 150 upper air stations was designated as the GCOS Upper-Air Network (GUAN). Designation helped incorporate climate requirements into meteorological service procedures and, for NMHSs, helped sustain support for these long-running sites. These networks provided the foundation for the Regional Basic Climatological Network (RBCN), which provides far greater spatial detail on the variability of climate.

By 2001, annual reports prepared by WMO indicated that the GSN and GUAN were in need of performance improvements. The GCOS System Improvement Programme, which is an element of the GCOS Cooperation Mechanism, has resulted in the renovation of over 30 GSN and 20 GUAN stations, in addition to providing over 25 station-years of radiosondes. The longer-term intent is to apply GCM funds to needs in the oceanic and terrestrial domains in addition to those in the atmospheric domain.

One of the great achievements in climate monitoring over the last 20 years has been the development of ocean observing systems. Knowledge of the global oceans today is partly the result of deployment of both in-situ and satellite systems.

The Pacific Tropical Atmosphere Ocean (TAO) array has been expanded to both the Atlantic and Indian tropics, providing real benefits in seasonal and inter-annual climate prediction. A global network of floats measuring many parameters, called the Argo Programme, reached its goal of 3000 floats in 2007 and currently has over 3500 floats in the water, measuring the temperature and salinity in the upper 1–2 km of the ocean.

spacer In addition a worldwide system of reference stations, known as OceanSITES, provides full- depth coverage at 60 sites for dozens of variables. Overall, the number of in-situ oceanographic reports has gone from roughly 4.5 million in 1999 to more than 16 million in 2009.

Figure 2: ECVs are relevant to understanding climate change, feasible and cost-effective

The satellite record of global sea level now stretches almost 20 years, from TOPEX/Poseidon through Jason-1 and Jason-2. Analyses from many international groups have converged on global mean sea-level rise rates of 3.1- 3.2 mm/year. The far longer Global Sea Level Observing System (GLOSS) network time series provides local variations in sea level and the long-term context of satellite measurements.

There has been notable progress in terrestrial networks for climate over the 20 years since GCOS was founded, particularly in cryospheric measurements. A time series of ice sheet mass balance from space now extends from 1992 to the present. The overall performance of in-situ glacier monitoring networks has been improving, as noted by the World Glacier Monitoring Service, while satellite-based glacier inventories have expanded considerably.

For other terrestrial measurements, the increased commitment of space agencies to produce fundamental climate data records from existing systems has led to improved availability of global datasets, such as of burned area, FAPAR, LAI, above-ground biomass, land cover, lakes and soil moisture. The community now increasingly uses these datasets.
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Figure 1: Observing systems underpin climate assessment, policy development and addressing adaption, mitigation and other climate services

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Both GCOS and the UNFCCC were established in 1992 and an enduring partnership between them has been in place ever since. Language on research and systematic observations was included in the text of the Convention in 1992 in Articles 4 and 5.

The original GCOS report on the adequacy of the global climate observing systems was requested by the UNFCCC in 1997. Additional interactions include the delivery in 2004 of the Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC and its 2010 update. The UNFCCC has been and remains a vital mechanism to bring issues of maintenance of the long-term climate record to the attention of governments in an international forum.


The GCOS Programme began working with regions to identify priority observing system needs following an invitation by the UNFCCC at the 5th Session of the Conference of the Parties in 1999 to organize a Regional Workshop Programme. This led to the preparation of Regional Action Plans in 10 regions of the world, prepared by experts from each region, and containing 10–15 project proposals addressing regional observing system priorities. In 2006, the GCOS Secretariat helped organise a major meeting with potential donors in Ethiopia to help find funding for these proposals. This meeting led to the establishment of the Climate for Development in Africa Programme, a programme that is now poised to assist funding of African observing system needs.

GCOS and Satellites

Satellites provide a vital means of obtaining observations of the climate system from a global perspective. A detailed global climate record for the future will not be possible without a major, sustained satellite component. There has been direct and intense interaction between the GCOS Programme and the satellite community over the entire history of GCOS.

One of the highlights of this interaction has been the development of a strong working relationship between GCOS and CEOS, the primary international forum for coordination of space-based EO. In 2006, space agencies, through CEOS, responded to the GCOS climate requirements by identifying 59 separate actions to be undertaken. In addition, CEOS requested, and was provided by GCOS with, a more detailed analysis of satellite climate observing needs in the form of the 2006 Satellite Supplement and its 2011 update.
spacer There has been an increasing interest in long-term satellite observations of climate. Many of the major EO platforms of the 1990s had climate observation as their major driver. However, there has been an increasing concern for continuity of the climate record, following the GCOS Climate Monitoring Principles.

GCOS has also been active recently in defining requirements for climate datasets, particularly in its Guideline for the Generation of Datasets and Products Meeting GCOS Requirements, which has been influential in the development of CGMS and the Global Space-Based Satellite Inter-calibration System (GSICS) implemented by WMO.

Satellite observations have become a fundamental part of GCOS and, when combined with sufficient ground-based measurements, provide a comprehensive view of the global climate.

Next Steps

In 2014, GCOS was reviewed by a board appointed by its sponsors, ICSU, WMO, IOC and UNEP. Its overall conclusion was:

“There is no doubt the GCOS Programme should be continued. It is indispensible. If it ceased to exist it would need to be re-created.”

The review made a number of recommendations for improving GCOS. Improvements are needed to better integrate the sustained observing system and ensure it will meet future requirements. For instance, the Tropical Pacific Observing System (TPOS) has been in place for 20 years. Motivated by challenges in sustaining key components of the observing system and evolution in observation requirements and technology, an international review recommended the TPOS 2020 project to make TPOS more robust, integrated and sustainable, and able to meet future needs. TPOS 2020 is now well underway.

GCOS has produced a status report reviewing progress of the Global Climate Observing System and outcomes of actions identified in the Implementation Plan. This Status Report will be submitted to the UNFCCC SBSTA at COP21.

GCOS is also preparing a new Implementation Plan to present to the UNFCCC SBSTA at COP22 in December 2016.
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Figure 3: Antarctic ice velocity from Rignot et al., combining multi-mission SAR data acquisitions coordinated by the IPY Space Task Group, with support from ESA, CSA, JAXA and NASA.

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Figure 4: The ESA CCI has released three global LC maps for the 1998–2002, 2003–2007 and 2008–2012 epochs and three global land cover seasonality products describing vegetation greenness, snow and burned area occurrence dynamics. All products can be freely accessed online at (picture: ESA). Credit: Land Cover_cci Project Team.

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spacer spacer Article Contributors

Carolin Richter and Simon Eggleston (GCOS)

Further Information


GCOS Publications:

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