In response to an increasing interest in terrestrial carbon and following a proposal led by the Global Terrestrial Observing System (GTOS), the Integrated Global Observing Strategy Partnership (IGOS-P) approved terrestrial carbon cycle as its second major theme in November, 1999. This report presents the results of a follow-up Terrestrial Carbon Observation (TCO) Synthesis Workshop, organized by GTOS in collaboration with the International Geosphere-Biosphere Programme (IGBP) and other IGOS-P members on 8-11 February 2000 in Ottawa, Canada. The workshop was designed to summarise existing information and observation requirements regarding terrestrial carbon, conduct initial evaluation of existing data or observations in relation to the requirements, identify major gaps or deficiencies, and propose solutions.
Existing stated requirements for terrestrial carbon information were reviewed in several areas, including international conventions, scientific understanding of the global carbon cycle and assessments of their evolution (current and into the future), and land management. Based on these, the needed observations were analysed with a view to satisfy a ‘dual constraint’ methodology for estimating terrestrial carbon fluxes, based respectively on a) local ecosystem models scaled up with satellite data, and b) atmospheric model inversions using concentration measurements of atmospheric CO2 and other tracer gases. The workshop also discussed existing observations, gaps, and needed improvements.
To meet TCO needs, the concept of an observing system was considered. Such a system will contribute to the integrated understanding and human management of the global carbon cycle through systematic, long-term monitoring of the terrestrial exchanges of greenhouse gases, especially CO2, and the associated changes in carbon stocks. The goal is to obtain estimates through the use of models that synthesise information from several types of measurements: atmospheric CO2 and other gases, surface fluxes, ecological, and remote sensing. These estimates will be provided with known and decreasing uncertainty, by systematic of cross-checking independent approaches and by designed expansions of current measurement networks. The information products will be of value not only at the global and regional levels, but also for land management and assessment in support of sustainable development at the national level. Ultimately, an integrated global observing strategy should provide near-real-time diagnosis of carbon sources and sinks at high resolution in both space and time that simultaneously satisfies all the data constraints (in situ, remotely sensed, and atmospheric) at multiple scales. Such a system will be more than a set of observations; rather, it will constitute a carbon cycle data assimilation system analogous to the observing systems currently used for temperature, precipitation etc. in operational weather prediction.
Based on the presentations and discussions, the workshop reached the following conclusions:
1. Information on the global distribution of terrestrial carbon sinks and sources is essential for policy and scientific purposes in four areas: reporting for multilateral environmental agreements; understanding of the carbon cycle; assessment of global change trends and impacts; and the management of ecosystem resources at local to regional levels.
2. A dual observation and modelling approach, based respectively on the inversion of atmospheric observations and on the use of satellite data and ecosystem models, is potentially capable of achieving accurate information on the distribution of carbon sources and sinks at all scales from landscape to global.
3. Many components needed for terrestrial carbon observations are well understood. Some are in place, others need to be augmented, and all need to be placed in a consistent, functioning framework.
4. To be effective, such a framework must incorporate both international coordination and national implementation as essential components.
Workshop participants made the following recommendations to IGOS-P:
1. Seek endorsement for the TCO system concept.
2. If the concept is adopted, modify the proposed evolution strategy, as appropriate, and take steps to its implementation. These steps should include an integrated approach to data distribution, quality control, and archiving; arrangements for the generation of core products; and clarifications regarding the responsibilities of agencies in the planning, development, and performance assessment of these activities.
3. Ensure continuation of existing satellite observations that are important to TCO into the foreseeable future. Accelerate the development and deployment of new satellite observation technology, including lidars for vegetation biomass, canopy structure, and atmospheric CO2 concentration.
4. Expand the system of flux networks and ensure adequate geographic coverage, continuity of observations, and coordination.
5. Improve the access and use of existing (non-flux) sites and national data sets for TCO purposes.
6. Review and further refine the strategy for the development of the dual constraint concept, and ensure active participation of the hydrological community in this process.
7. Give high funding priority to research and development of instruments, observation methods, and models related to carbon cycle observations.
8. In the evolution of terrestrial carbon observations, maintain close linkages with the ocean carbon cycle observation community.
9. Issues relating to scaling, gridded data sets, emissions, and others identified at this workshop should be examined by a broader scientific community in order to understand the implications for global terrestrial carbon observations.
