The United Nations Framework Convention on Climate Change (UNFCCC) has repeatedly identified the urgent need for improving the availability and access to systematic global observations of climate variables for the purposes of the Convention. In response, the Global Climate Observing System (GCOS) Secretariat has prepared a preliminary analysis of availability and accessibility of atmospheric and hydrological data relevant to climate, from the perspective of the monitoring and archiving centres. This analysis is based on an empirical survey carried out among managers of data archive and monitoring centres, primarily those associated with the GCOS baseline networks.

It has become clear in our study that, despite a number of deficiencies, the infrastructure for global data exchange exists for meteorological, including atmospheric composition, climate variables. Designated monitoring and data archive centres are in place that allow easy access to climate datasets. In the hydrological domain, a designated international data centre is in place only for river flow properties, and large gaps exist in the receipt of data from existing networks. Substantial effort is still required in terms of hydrological data standardization (e.g., improved metadata), standard operating practices, data policy, infrastructure, and awareness. The situation is better in the related cryospheric domain, where designated monitoring and archive centres are operating.

The major problems and challenges identified in this study include:

· Reluctance of some countries to exchange data, due to a number of reasons;

· Need to improve the awareness of climate requirements for global data exchange;

· Technical problems in preparation, transmission and receipt of climate messages;

· Resource limitations in developing countries and, to some extent, in archive and monitoring centres;

· Data and metadata standardization and data stewardship.

The existing situation could be improved by increasing awareness, on the political and scientific level within countries and funding agencies, of the importance and benefits of the free and unrestricted data exchange for climate purposes. Continuing encouragement is required from international bodies (e.g., WMO, UNFCCC) for efforts by the international data centres to obtain permission from countries for the release of data and the rescue of historical climate records. A clearer expression of requirements for global climate data by the climate science community would be useful in discussing with countries the needs to exchange data.

Data management, stewardship, and long-term access to data were seen as crucial by the data centres. The international data archive centres are major assets in providing for free access and distribution of climate data and products, and therefore require sustained long-term funding. In addition, the monitoring centres are essential to maintain the quality and regular receipt of data, through the capability to provide timely and appropriate feedback to observers. Furthermore, there was an emphasis on the need for consistent time series of climate observations, which are made more feasible by technological progress.