Posted May 2000
Jeff Tschirley, Josef Cihlar, Scott Denning and Rene Gommes
Respectively affiliated with: the Global Terrestrial Observing System, the Canadian Centre for Remote Sensing, Colorado State University, and the Food and Agriculture Organization of the United Nations.
The need for systematic assessment of carbon pools has become more important as countries realize that their status as a net "sink" or a "source" of carbon vis-à-vis UNFCCC and the Kyoto protocol has implications for their future economic development. Policy-makers are also understanding that a large portion of the global annual net primary ecosystems productivity is found in economic spheres such as forests, cropland and pasture.
At their fourth meeting (Stockholm, November 1999), the Integrated Global Observing Strategy Partners (IGOS-P) approved terrestrial carbon as a theme for which a systematic global observation initiative should be developed under the leadership of the Global Terrestrial Observing System (GTOS). They also approved a process whereby terrestrial requirements will be integrated with the ocean carbon observation requirements being developed in the IGOS ocean observation theme.
Although carbon pools and their long-term changes will be at the heart of ongoing negotiations under the UNFCCC, there is also a need to estimate carbon fluxes that are of a more short-term nature. The reason is that the consistency and reliability of our data on carbon pools can only be validated using models that in turn highlight the gaps in our current knowledge. They are also useful for identifying new observation requirements that can lead to greater confidence in both the pool and the flux data.
Because many factors interact to affect the carbon cycle, both above and below the soil surface, information on terrestrial carbon must be obtained frequently and with a high spatial resolution. Given the limitations of measurement techniques, this has not been possible in the past. New methods, including observing techniques and process-oriented models, now make the problem more tractable. This is a major reason for the increasing research interest in the observation and quantification of terrestrial carbon.
To consolidate and systematize global observations of terrestrial carbon, there is a need to agree on the observation and modelling requirements; to harmonize the main relevant projects and activities that can contribute to a global observing 'system'; and to identify gaps and ways to fill them. The Terrestrial Carbon Observation (TCO) initiative aims to meet these needs.
The number of programmes and initiatives concerned with this topic is steadily increasing, at national, regional and global levels. Some have a strong observational base and include satellite data, while others are based on modelling or on local measurements using a sampling strategy.
Some requirements for estimating terrestrial carbon are well understood, although in certain cases the continuity of their measurement is of concern. They include: land cover and land cover change, leaf area, biomass burning (fire scars), solar radiation, atmospheric composition, surface fluxes, and crop and forest production. The observational requirements for these issues have been established through various experiments and regional studies.
Other observations are less well understood and techniques for their measurement may not be sufficiently developed. While progress has been made in some cases, further work is needed before global observations can be implemented. The most important remaining issues are: biomass and its changes, canopy structure, atmospheric CO2 concentration at a micro-scale, plant biogeochemistry, and meteorological parameters with a fine spatial resolution.
The importance of these observations is generally accepted by scientists and, to varying degrees, the observation techniques have also been developed. However, there is a lack of experience in dealing with these types of data and therefore with the derivation of appropriate biophysical variables for use in carbon exchange models. Thus, further research and technology development are also necessary.
There is a need to move beyond the current approach whereby process models are tested on a very small scale, pronounced to be valid and then extended to the global scale. An observation network is needed that allows the development and testing of both process-based ecosystem models, their extrapolation to larger scales, and the assessment of subcontinental-scale flux variability.
The TCO design must support a range of observation and modelling requirements and must be developed with the involvement of the observation and modelling specialists as well as representatives from the policy-making community.
A programme of work has been established to launch TCO. A meeting in Ottawa in February 2000 developed the initial observation requirements. A meeting in Portugal in May has built upon that work. A team of scientists and policy-makers has been established to contribute to various parts of the Terrestrial Carbon Observation initiative. Its success will depend upon close collaboration and a shared sense of priority among the key partners - the observing systems, the international scientific community, UN organizations and the space agencies.
Additional information about TCO can be obtained from the GTOS Secretariat or e-mail: email@example.com