In December 1997 in Kyoto, Japan, the community of nations reached a historic agreement to collectively curb the growth of carbon dioxide and other radiatively active gases in the atmosphere. The intense 1997–1998 El Niño, although not necessarily related to the carbon dioxide increase, made clear the importance of climate variations. The event caused anomalous weather, some of it beneficial (fewer hurricanes in the Atlantic), but much of it adverse (record rainfall in the western and southern portions of the United States and drought in Indonesia). Agriculture, ecosystems, water supply systems, and public health are potentially vulnerable to natural variability and changes in climate. The leaders of the developed and developing nations recognize that climate changes are likely to have significant impacts on their economies, foreign policies, and quality of life in the coming decades.

The 1997 Conference on the World Climate Research Programme to the Third Conference of the Parties of the United Nations Framework Convention on Climate Change concluded that the global capacity to observe the Earth's climate system is inadequate and is deteriorating worldwide: ''Without action to reverse this decline and develop the Global Climate Observation System, the ability to characterize climate change and variations over the next 25 years will be even less than during the past quarter century" (See Appendix A). As a result, the chair of the subcommittee of the U.S. Global Change Research Program (USGCRP) requested a National Research Council study to assess the current status of the climate observing capabilities of the United States. This report focuses on existing observing systems for detection and attribution of climate change, with special emphasis on those systems with long time series.

As will be shown in this report, these systems require immediate action to reverse their decay and to redesign them.

Climate impacts most economic sectors, including energy, food and fiber, transportation, human health, biological resources, and living conditions. These activities are influenced by precipitation and water availability, temperature, storms, solar radiation, and sea level, and how they vary over time and with geography. Variables most useful for climate change detection and attribution are: three-dimensional temperature and water vapor; surface wind, sea level pressure, precipitation; sea ice and ice sheet properties; streamflow, groundwater and land water reservoirs; vegetation cover; and ocean upper-level temperature and salinity, deep ocean temperature and salinity profiles and the height of sea level.

Most observing systems that monitor climate were established to provide data for defined purposes, such as predicting daily weather; advising farmers; warning of hurricanes, tornadoes and floods; managing water resources; aiding ocean and air transportation; and understanding the role of the ocean in climate change. Many federal and state agencies, including the Departments of Agriculture, Commerce, Defense, and Interior, and NASA, collect these data. In some departments, several agencies operate observing systems. For example, in Defense, the Air Force, Navy, and Corps of Engineers operate networks that observe some of these variables.

The purpose of these observations continues to evolve with changes in mission, with the development of new technologies, and more recently with restrictions on budgets. The priorities to maintain the observation networks vary widely from agency to agency. In general, management of the programs has not recognized the importance of the observations for detection and attribution of climate change. The departments and agencies should strengthen and revitalize the partnerships that generated long-term records of many of these variables.

Climate researchers have used existing, operational networks because they have been the best, and sometimes only, source of data available. They have succeeded in establishing basic trends of several aspects of climate on regional and global scales. Deficiencies in the accuracy, quality, and continuity of the records, however, still place serious limitations on the confidence that can be placed in the research results. Federal agencies should undertake a joint effort to improve the observations from these networks.

The panel concludes that the ten climate monitoring principles proposed by Karl et al., 1995, should be applied to climate monitoring systems:

1. Management of Network Change: Assess how and the extent to which a proposed change could influence the existing and future climatology

• obtainable from the system, particularly with respect to climate variability and change. Changes in observing times will adversely affect time series. Without adequate transfer functions, spatial changes and spatially dependent changes will adversely affect the mapping of climatic elements.
• Parallel Testing: Operate the old system simultaneously with the replacement system over a sufficiently long time period to observe the behavior of the two systems over the full range of variation of the climate variable observed. This testing should allow the derivation of a transfer function to convert between climatic data taken before and after the change. When the observing system is of sufficient scope and importance, the results of parallel testing should be documented in peer-reviewed literature.
• Metadata: Fully document each observing system and its operating procedures. This is particularly important immediately prior to and following any contemplated change. Relevant information includes: instruments, instrument sampling time, calibration, validation, station location, exposure, local environmental conditions, and other platform specifics that could influence the data history. The recording should be a mandatory part of the observing routine and should be archived with the original data. Algorithms used to process observations need proper documentation. Documentation of changes and improvements in the algorithms should be carried along with the data throughout the data archiving process.
• Data Quality and Continuity: Assess data quality and homogeneity as a part of routine operating procedures. This assessment should focus on the requirements for measuring climate variability and change, including routine evaluation of the long-term, high-resolution data capable of revealing and documenting important extreme weather events.
• Integrated Environmental Assessment: Anticipate the use of data in the development of environmental assessments, particularly those pertaining to climate variability and change, as a part of a climate observing system's strategic plan. National climate assessments and international assessments, (e.g., international ozone or IPCC) are critical to evaluating and maintaining overall consistency of climate data sets. A system's participation in an integrated environmental monitoring program can also be quite beneficial for maintaining climate relevancy. Time series of data achieve value only with regular scientific analysis.
• Historical Significance: Maintain operation of observing systems that have provided homogeneous data sets over a period of many decades to a century or more. A list of protected sites within each major observing system should be developed, based on their prioritized contribution to documenting the long-term climate record.
• Complementary Data: Give the highest priority in the design and implementation of new sites or instrumentation within an observing system to data-poor regions, poorly observed variables, regions sensitive to change, and

• key measurements with inadequate temporal resolution. Data sets archived in non-electronic format should be converted for efficient electronic access.
• Climate Requirements: Give network designers, operators, and instrument engineers climate monitoring requirements at the outset of network design. Instruments must have adequate accuracy with biases sufficiently small to resolve climate variations and changes of primary interest. Modeling and theoretical studies must identify spatial and temporal resolution requirements.
• Continuity of Purpose: Maintain a stable, long-term commitment to these observations, and develop a clear transition plan from serving research needs to serving operational purposes.
• Data and Metadata Access: Develop data management systems that facilitate access, use, and interpretation of data and data products by users. Freedom of access, low cost mechanisms that facilitate use (directories, catalogs, browse capabilities, availability of metadata on station histories, algorithm accessibility and documentation, etc.), and quality control should be an integral part of data management. International cooperation is critical for successful data management.

The panel's evaluation of existing climate records, using these ten principles, shows that only about half of the principles are being followed for some of the variables most useful for climate change detection and attribution. For other records, only one or two principles are being followed adequately. The application of all but one of the principles of climate monitoring needs improvement.

If federal agencies are to serve society's needs for well-informed climate decisions, they should strive to preserve the value of the past climate record and to build improved and more valuable climate records in the future. Although this report focuses on existing observational systems, especially those with long data records, it is important to stress that this represents only a part of the needs for climate data. Programs to develop new records also should be undertaken, and should take advantage of such new technology as geostationary and polar orbiting satellites.

A word of caution, however: for many years, satellite remote sensing has been suggested as the answer to climate monitoring. Indeed, the growing emphasis on operational mesoscale weather observing and forecasting initiatives inevitably will lead to a growing reliance on remote sensing—both surface- and space-based. If, in the process, in situ networks such as the radiosonde are reduced in size or importance, there could be a large negative impact on the ability to assess climate and climate change. The panel recognizes that many of the atmospheric observations in ocean areas can be provided only by global systems such as satellites. At the moment, however, there is only sketchy information on the suitability of remotely sensed data as a source for climate change detection and attribution. Some studies have shown a positive impact of

these data. Others have clearly indicated substantial problems, two of which are calibration and poorly documented changes in the instrument performance from one satellite to the next.

FINDING: There has been a lack of progress by the federal agencies responsible for climate observing systems, individually and collectively, toward developing and maintaining a credible integrated climate observing system, consequently limiting the ability to document adequately climate change.

RECOMMENDATION: These agencies should work through the USGCRP process and at higher government levels to:

• stabilize the existing observational capability;
• identify critical variables that are inadequately measured;
• build climate observing requirements into the operational programs as a high priority;
• revamp existing climate programs and some climate-critical parts of operational observing programs through the implementation of the ten principles of climate monitoring; and
• establish a funded activity for the development, implementation, and operation of climate-specific observational programs.

In the near term, the USGCRP agencies can ameliorate this situation by taking the following actions:

1. All agencies operating climate-relevant observation systems should adopt and implement the set of climate monitoring principles outlined above.
2. System performance measures should be developed and monitored on a regular basis. It would be unwise to wait for a major environmental assessment or data archeology effort to discover that problems that occurred 10 or 20 years earlier had already inflicted considerable damage on the climate record. An institutional infrastructure should be developed to assess the quality of data sets and correct problems as they occur.
3. Accelerate access by the research community to climate-related observation data bases, primarily in non-electronic formats, that reside deep in agency archives.
4. The free, open, and timely exchange of data should be a fundamental U.S. governmental policy and, to the fullest extent possible, should be enforced throughout every federal agency that holds climate-relevant data. Adherence to this principle should be promoted more effectively by the U.S. government in its international agreements, with particular attention given to implementation.
5. Vastly improved documentation of all changes in equipment, opera-

• tions, and site factors in operational observing systems is required to build confidence in the time series of decadal-to-centennial climate change.
• Establish and maintain strong, robust links between operational systems managers and the climate data users.
• Because U.S. economic and social interests depend on knowing the climate globally, U.S. agencies should pursue international cooperation in climate observation and monitoring through international mechanisms. USAID funds may be one vehicle to ensure critical observations in developing countries.