management approach will be widely applicable. There are explicit lessons to be learned both from its current success and from the challenges it faces in the future as it scales up its data management efforts.

CDIAC is a part of ORNL's Environmental Sciences Division. It was founded in 1982 by DOE to provide identification, collection, quality assurance, documentation, and distribution for information on the bio-geochemistry of carbon dioxide and the effects of carbon dioxide on vegetation and on the Earth's climate. The scope of CDIAC was subsequently expanded to include related global change topics, such as other greenhouse gases and the effects of climate change on the environment.

Other programs not part of CDIAC, but within the Environmental Sciences Division, include the Atmospheric Radiation Measurement (ARM) archive, which will hold large data volumes (1 to 5 terabytes/year) related to general circulation models (specifically, the representation of clouds and of moisture, heat, and energy transfers therein) and derived from high-speed, real-time samplers. The Environmental Sciences Division also houses a NASA Distributed Active Archive Center, which focuses on ground-based field program data (e.g., carbon in soils, vegetation cover). In large part, this Distributed Active Archive Center was sited at ORNL because of CDIAC's past experience and success, which may be expected to be incorporated and extended into the ORNL DAAC's data management scheme.

ORNL is facing significant technical and organizational challenges as it attempts to implement the new functions associated with the ARM Program and the Distributed Active Archive Center. These challenges are representative of those faced by the global change research community as large volumes of data from new sources become increasingly available. ORNL's experience with CDIAC is relevant and valuable, but these two new programs are different in important ways. First, data volumes will be much larger than those with which CDIAC staff are accustomed to dealing. Second, these programs will focus on real-time rather than historical data. Third, ORNL will be serving a much larger audience and will not be as close to the user community as CDIAC's staff currently is. Finally, ORNL will not always have the luxury of time that is now available to CDIAC to build relationships, perform intense quality assurance and quality control, and produce value-added products.

VARIABLES MEASURED AND SOURCES OF DATA

CDIAC produces aggregate data sets that summarize global and regional production of greenhouse gases such as carbon dioxide and methane; trace gas measurements in the atmosphere and oceans; long-term climate records in addition to temperature (e.g., precipitation, clouds,



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