ceos   eesa
Our Changing Climate
  The Important Role of Earth observations  
  Future Challenges  


Without the capabilities offered by satellite Earth observations, there would be insufficient information for future climate change studies and insufficient evidence with which to inform our decision-making on policies aimed at mitigation and adaptation to climate change. We would also have no way of checking the effectiveness of our mitigation strategies in terms of the trends of key Essential Climate Variables. Earth-based measurement systems alone cannot provide the synoptic global picture which is required.

Thanks to the work of GCOS, with its sponsors and partners in support of the UNFCCC, we have established a clear community consensus on the observations that are required to deliver 45 Essential Climate Variables needed to detect, monitor, predict, adapt to and mitigate climate change in the Earth System. CEOS and GCOS together have identified 25 of the Essential Climate Variables which are largely dependent on satellite observations and have specified a number of actions required to ensure the necessary continuity or technical characteristics required for climate studies.

The vision of a global observing system for climate will only be realised through a well planned and sustained international coordination effort, involving a number of challenges:

Ensuring satellite Earth observing systems are designed, constructed and operated in a way that enables more effective climate observations.
For the most part, satellite observations of climate are not sufficiently accurate at present to establish a climate record that is indisputable, and hence capable of determining whether, and at what rate, the climate is changing, or of testing the long term trend predictions of climate models. Space-based observations do provide a clear picture of the relatively large signals associated with inter-annual climate variations such as El Niño, and they have also been used to diagnose gross inadequacies of climate models, such as their cloud generation scenarios. However, satellite contributions to measuring long term change have been limited, and, at times, controversial, as in the case of differing atmospheric temperature trends derived from microwave radiometers.

Measuring long-term global climate change from space is a daunting task. The climate signals we are trying to detect are extremely small: e.g. temperature trends of only a few tenths of a degree C per decade, ozone changes as little as 1% per decade and variations in the Sun’s output as tiny as 0.1% per decade or less. Current satellite systems are not up to the task. Sensors and onboard calibration sources degrade in orbit, measurements are not made to international standards, long term data sets must be stitched together from a series of overlapping satellite observations, orbital drift introduces artefacts into long-term time series, and insufficient attention is paid to meeting the high accuracy, high stability instrument requirements for monitoring global climate change.

To assist space agencies in this challenge, GCOS has defined a series of GCOS Climate Monitoring Principles (GCMPs – see Annex B). GCOS notes that for satellite data to contribute fully and effectively to the determination of long-term records, they must be implemented and operated in an appropriate manner to ensure adequate stability and accuracy, and with steps to ensure homogeneous products. The GCMPs require:

— continuity and overlap of satellite observations;

— enhanced orbit control;

— calibration and instrument characterisation;

— sampling strategy;

— sustained generation of products, data analysis, and archiving.


Risk of human-induced desertification.

Since most existing Earth-observing satellite systems were not specifically designed for climate monitoring, there is, as yet, no systematic process for the application of the GCMPs. As part of the response to the GCOS IP, CEOS space agencies have undertaken to address this challenge and to assemble the resources and political will required to better coordinate,design, operate, process, store and distribute satellite measurements that satisfy the GCMPs.

Achieving satellite instrument calibration for measuring global climate change.
A powerful new paradigm for achieving satellite instrument calibration suitable for measuring long term global climate change has recently emerged. The basic concept is to place in space a series of highly accurate benchmark instruments in order to measure with high spectral resolution the energy reflected and emitted by the Earth. These instruments would provide reliable long term records of climate forcings, response and feedbacks to monitor climate change. Their records would also serve as the validation data needed to test and evaluate climate model predictions. The benchmark instruments would also constitute a reference standard, or calibration observatory, in space that can be applied to other environmental satellite sensors that are not as well calibrated, e.g. the sensors on operational weather satellites. Such calibrations can be performed by comparing coincident observations of the benchmark instruments with the other sensors. These spectral instruments would be joined in space by several other critical benchmark measurements.

The Global Space-based Inter-Calibration System (GSICS) is a new international programme to assure the comparability of satellite measurements provided at different times by different instruments that are the responsibility of different satellite operators. Sponsored by the World Meteorological Organisation and the Coordination Group for Meteorological Satellites, GSICS will inter-calibrate the instruments of the international constellation of operational low Earth orbiting (LEO) and geostationary (GEO) environmental satellites and tie these to common reference standards. The inter-comparability of the observations will result in more accurate measurements for assimilation into numerical weather prediction models, construction of more reliable climate data records and achieving the societal goals of the Global Earth Observation System of Systems (GEOSS). GSICS includes globally coordinated activities for pre-launch instrument characterisation, on-board routine calibration, sensor inter-comparison by collocation of individual scenes or overlap between time series, and use of Earth-based or celestial references, as well as field campaigns. An initial strategy uses highly accurate research satellite instruments as space-based reference standards for inter-calibrating the operational satellite sensors.

Transitioning from science-focused missions to operational services.
If space agencies are to supply the sustained and coordinated observations of the 25 Essential Climate Variables required by the UNFCCC and IPCC, challenges related to the way in which the Earth observation sector is structured must first be addressed. Research space agencies tend to do new things once; operational agencies, whilst adopting new technologies and useful advances as they become available, do more or less the same things over and over. If continuity is to be ensured, more climate variables must be classified and recognised as operational, and made the responsibility of an operational agency or supported as operational in other ways. Wherever possible, operational measurements should be specified so that they satisfy the stated needs of the climate community.

In recent years, CEOS agencies have endeavoured to ensure continuity of some key measurements. For example, in ocean surface altimetry, the key agencies (CNES, EUMETSAT, NASA and NOAA) have cooperated to attempt to ensure continuity of measurements so that they may become established as near-operational within some user communities. This remains, however, the exception rather than the rule for research-oriented space agencies, which are neither mandated nor funded to provide operational services. Europe’s Global Monitoring for Environment and Security (GMES) programme is a promising example of how this transition might occur, with the emergence of operational services in support of European environmental policy that are being provided through a partnership of the European Commission (EC) and the European Space Agency (ESA). Without such initiatives, the resources and mandates of space agencies as they currently stand will be insufficient to meet UNFCCC needs.

Improving access to existing climate data records generated by satellites.
All countries must be able to benefit from the use of climate data records. This is an important issue in relation to products that depend primarily upon satellite observations. While Earth observation from satellites is a costly activity to which only a small number of countries are currently able to contribute, the derived information is generally of global utility. To meet the needs of the UNFCCC, action needs to be taken to allow global access to these products and to ensure their global utility.

Strengthened and rationalised coordination mechanisms.
CEOS is recognised as the primary international forum for coordination of the Earth observation programmes of space agencies worldwide. If space agencies are to mobilise the substantial response demanded by the challenge of both the GCOS Implementation Plan and the GEOSS Implementation Plan, then such a coordination role will be increasingly important. CEOS recognises the need to improve its coordination role and activities above the current ‘best efforts’ arrangements.

As climate change gains political importance and governments support the GCOS and UNFCCC assessment of the importance of Earth observations in its study and adaptation, we might expect changes in space agency policy, so that their terms of reference recognise improved coordination and climate needs and, not quite so strictly, the current emphasis on defined operational roles or advances in industrial technology. We also might expect a significantly higher priority and resources assigned to the kind of role which CEOS is providing, or has the potential to provide. Further, we should expect political direction for a clear assignment of the roles and responsibilities of the various coordination groups which exist – including CEOS, CGMS (Coordination Group on Meteorological Satellites) and others – to find new levels of efficiency through improved focus and larger critical mass. This is essential if we are to see the improved optimisation of the overall observation strategy required to meet the needs determined by GCOS and GEO.




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