EXECUTIVE SUMMARY

The objective of the TOPC Plan is to provide a rationale for the structure and implementation of the initial observing system. It describes the minimum set of terrestrial^[1] observations that are required to detect, predict and to assess the impacts of climate change. Annex I to the document contains a detailed description of each of the variables. While it has taken considerable work to arrive at a consensus on this set of variables, it is recognized that these are a beginning, to be refined as our understanding of the observational requirements and capabilities improves. The Plan recognizes that a comprehensive observing system must address the critical variables by making measurements with sufficient accuracy, spatial and temporal resolution, and long-term continuity. The data must be compiled and collated in a fashion that is useful to the users. Ultimately, the products that are generated by GTOS and others must include ones that are in a form that can be easily utilized by policy- and decision-makers. For much of the land and climate system, such comprehensive observations, databases and associated products are not yet available.

In spite of the fact that a considerable amount of work needs to be done before a comprehensive observation system can be completely implemented for the terrestrial components of the GCOS or the climate change portion of the GTOS, a number of actions can be taken to begin implementing some of the required observations. Those observations which can be made from satellites offer the best hope of globally consistent data sets, and consequently research to increase the number and quality of observations that can be made from space is highly encouraged. At the same time, these data must be made readily available to countries that do not have a programme of space-based observations.

It was recognized that many hundreds of variables are potential candidates for global monitoring and there are many thousands of potential sample locations. However, it is neither feasible nor desirable to measure everything, everywhere, all the time. This reality led to a five-tier hierarchical sampling scheme in which at the one extreme a few variables are measured infrequently at many locations and at the other extreme a large number of variables are measured frequently at a few locations.

Regarding in situ measurements, most of the requirements are already being made at a number of sites that clearly fall within the proposed sampling scheme. Existing sites have been contacted as part of the development of the overall plan for GTOS, and from those sites willing to participate, the ground-based observations should be implemented as soon as possible. Making historical data from these sites available via the Internet should also receive high priority. Working with the GCOS/GTOS/Global Ocean Observing System (GOOS) Data and Information Management Panel, a network-based system for data management must be developed over the next year and a half. It is expected that this system should work in close cooperation with the International Geosphere-Biosphere Programme - Data and Information System (IGBP-DIS) and UNEP's Global Resource Information Database (GRID) programme. The system must provide access to both space-based and in situ observations.