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Policy imperative for a global carbon observing system has been well established.

Through international negotiations, national governments have agreed to numerous conventions and multilateral agreements that specify or imply the need for carbon cycle information and therefore systematic, long-term observations. At the present time, the relevant conventions include: the United Nations Framework Convention on Climate Change (UNFCCC) and the associated Kyoto Protocol; the Convention on Biological Diversity; the Convention to Combat Desertification; Agenda 21 (agreed to at the 1992 United Nations Conference on Environment and Development); and the Global Plan of Action for the Protection of the Marine Environment from Land-Based Activities. These and other conventions identify needs and objectives to be satisfied through coordinated international efforts.

To meet their obligations under the conventions, national governments and international organizations need sound, consistent information on the terrestrial and atmospheric aspects of the carbon cycle and the factors that affect it. For example, land cover and use as well as their changes are essential to most of the conventions. Conventions require assessments of the current status, detection and projection of trends, and the implications from a policy perspective. Such evaluations are conducted for example by the Intergovernmental Panel on Climate Change in response to policy needs, based on published results of analyses that in turn depend on systematic global observations. It should be noted that the conventions also make provisions for observations; for example, UNFCCC (COP 5) has called on Parties to undertake systematic observation and research. UNFCCC requires transparent and verifiable reporting, and this will likely also apply to the Kyoto Protocol. A globally consistent, data-based approach such as proposed for the terrestrial carbon theme (Chapter 4) is well suited to satisfy this requirement.

It is important to note that while recent policy discussions have concentrated on the potential role of specific terrestrial sinks, the fundamental policy issue is the impact of increasing atmospheric concentration of trace gases. The increase depends on the uptake by the entire biosphere and is modulated by local land use actions. Improved understanding of the carbon cycle also necessitates consideration of the biosphere as a whole (IGBP Carbon Working Group, 1998; see also below). For these and other reasons, the proposed concept for terrestrial carbon observation (Chapter 4 and 6) encompasses the entire terrestrial biosphere and its interaction with the atmosphere. It also addresses the land use-dependent sink/source role of the biosphere through land cover and land use products at appropriate spatial scales (p.12), thus providing the framework for ecosystem-specific carbon estimates.

A well-established need exists for information on the biosphere to support sustainable development and resource management.

Knowledge of the carbon cycle, especially terrestrial productivity, has long been vital to manage the biospheric resources upon which human societies depend. Appropriate management is particularly important for countries whose economic and social structures depend on production or subsistence agriculture. This motivation becomes stronger as a large and increasing portion of the net primary production is employed in the economic sphere (~ 40%; Vitousek et al., 1986), and is further strengthened by continuing concerns about the long-term sustainability of managed terrestrial ecosystems in the face of threats from salinity, soil impoverishment and erosion.

Terrestrial carbon information is thus important from both public and private enterprise perspectives, but with different emphases. From the public perspective, governments are seeking policy instruments (either administrative or financial) to improve land use and land management practice, reduce or reverse trends towards the degradation of natural resources, and lessen the impact of natural disasters such as drought. The design of these instruments depends on reliable, detailed observations and predictions about the linked cycles of carbon, water and nutrients upon which human use of the terrestrial biosphere depends. From the perspective of private enterprise, information is typically needed at a detailed and local level (for instance to manage a project for maximum productivity and minimum leakage of contaminants or to support carbon trading). However, larger-area information is also necessary to interpret local information and use it in strategic planning. The importance of the interplay between public and private institutions is clearly evident in the post-Kyoto developments, with financial implications for the management and trading of terrestrial carbon stocks.

Improved knowledge of the carbon cycle, its variability, and its likely future evolution is essential.

There are large uncertainties in the magnitudes and locations of carbon fluxes between the land, oceans and the atmosphere. Current observations indicate that on average, 55% of the released fossil fuel emissions accumulates in the atmosphere, and that the carbon removed from the atmosphere is roughly partitioned equally between oceanic and (mostly northern hemisphere) terrestrial systems. Also, land sinks are more variable from year to year, in response to climatic as well as human factors.

We presently lack the understanding and observations needed to close the annual carbon budget at the global level. Furthermore, it is not possible to unambiguously determine the spatial (geopolitical) distribution of carbon sinks, and previous attempts to do so have suffered from an inadequate data base. Remedial programmes are being established in some regions; while these are important steps, they cannot take the place of a coordinated global observing system. Based on recent international research activities, it is evident that further progress in our understanding of the global carbon cycle and its likely future evolution depends on improved observations of the terrestrial carbon processes. For example, in a special issue reporting results of an IGBP model intercomparison, Cramer and Field (1999, p. iv) stated “...At the heart of these (efforts) are enhanced experimental and monitoring systems (flux measurements, satellite sensors, field and laboratory experiments, global data archives) which are being identified by every single paper in this collection as being important for better parameterization of terrestrial biosphere models”. Improvements in models of the carbon cycle are essential for better projections regarding its behaviour, a critical pre-requisite for future policy discussions and measures. Conversely, improved understanding of the carbon cycle and the resulting models will facilitate increases in the efficiency and effectiveness of the observing systems and reporting procedures.

In addition,

Capability to observe key components of the carbon cycle and its dynamics has been established.

The capabilities for making atmospheric, ocean, and terrestrial carbon cycle observations have grown dramatically over the last 20 years. Global and regional atmospheric trace gas concentration measurement programmes have been operating for many years, and the quantity and quality of measurements has been steadily improving. In the terrestrial domain, similar advances in satellite remote sensing have led to global and regional products of land cover, fire, and measures of vegetation productivity. National and regional terrestrial networks are working through GTOS and FLUXNET to achieve consistent worldwide coverage. In parallel, numerical models of combined atmosphere-ocean-land system have advanced rapidly, keeping pace with the increasing speed and capacity of super-computing technology. Effective use and further improvements of these models directly depend on systematic global observations.

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