The U.S. Climate Reference Network:
A national automated baseline reference network to monitor climate change
For the next 50 years
C. Bruce Baker,
National Climatic Data Center, NOAA/NESDIS
Asheville, NC 28801
ABSTRACT
Recent assessments of U.S. and global climate monitoring systems have emphasized the
importance of accurate and representative meteorological data to detect climate variability but
have concluded that current observational networks are inadequate to achieve this goal. The U.S.
Climate Reference Network (CRN) is being created to correct these shortcomings and to meet
the challenge of climate monitoring and climate change detection in the U.S for the next 50-100
years. The CRN initiative is being led by the National Oceanic and Atmospheric Administration
(NOAA) National Climatic Data Center (NCDC). When fully deployed, the CRN will consist of
approximately several hundred automated stations across the 50 States and U.S. territories. The
initial variables being measured are temperature, precipitation solar radiation, surface
temperature and wind speeed. Wind speed is being measured at the height of the temperature
sensors for development of thermal transfer functions to relate CRN temperature measurements
to historical temperature observations at nearby stations in existing networks. The system has
been designed to accommodate additional (automated) sensors as resources permit. CRN
observations will be transmitted via GOES satellite near-real time on an hourly basis and
summary of day and summary of month statistics will be computed and transmitted near-real
time over internet by the NCDC.
Several organizations (NESDIS, OAR, NWS , the U.S. Department of Agriculture, the
NOAA Regional Climate Centers (RCCs), and State Climatologists, among others) contributed to
the establishment of CRN requirements and specifications which can be viewed via the web at the
following url:
http://lwf.ncdc.noaa.gov/oa/climate/research/crn/crnmain.html
In addition to establishing the project requirements and specifications, accomplishments during
the initial fiscal year (FY 2000) include establishing the communications and data ingest systems
and deploying the initial station pair in western North Carolina. The Atmospheric Turbulence and
Diffusion Division (ATDD) of the NOAA Office of Atmospheric Research performed the
engineering, laboratory calibration, field intercomparison, and deployment of the FY 2000FY2002 stations. The National Center for Atmospheric Research (NCAR) performed the initial
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evaluation of potential precipitation gages and to determine the optimal wind shield arrangement
to minimize wind-induced undercatch.
1.
INTRODUCTION
In recent decades, increasing attention has been paid to the issue of climate change, especially
global warming (or greenhouse warming). Reports by the World Meteorological Organization
(WMO, 1966, 1986, 1993), the Intergovernmental Panel on Climate Change (IPCC 1990, 2001), and
the U.S. National Research Council (NRC, 1999), have emphasized the importance of monitoring
climate in order to determine past climate variability, evaluate current climate change, and improve
climate models to produce more accurate predictions of future climate change. These reports have
expressed concern with the inadequate climate observing capabilities in many countries, including the
United States.
Most countries have station networks which observe atmospheric variables in support of the
WMO World Weather Watch Global Climate Observing System, or GCOS (WMO, 1988, 1989). In
the United States, many federal agencies have observing systems that monitor weather or climate for
specialized (mostly non-climate change) purposes (National Research Council [NRC], 1999).
Examples include the National Science Foundation (NSF) Long-Term Ecological Research (LTER)
network, the USDA Soil Climate and Analysis Network (SCAN) and snow pack telemetry (SNOTEL)
network, the National Oceanic and Atmospheric Administration (NOAA) Global Positioning
Satellite-Integrated Precipitable Water (GPC-IPW) network, and the National Weather Service
(NWS) upper-air, Automated Surface Observing System (ASOS), and Cooperative (COOP) Station
networks. Of these, the COOP network is best suited for climate monitoring purposes because many
stations have records extending back into the 19th Century. However, it suffers from many problems
including inadequate instrumentation, antiquated data handling systems, and historical data
inhomogeneities due to changes in instrumentation, location, and observation practices (NRC, 1999).
In spite of the United States being a leader in climate research, we do not have an observing network
capable of ensuring long-term climate records free of time-dependent biases. The accuracy and
fidelity of the data used to measure climate variability are crucial to government monitoring efforts
and to U.S. industry. Even small biases can alter the interpretation of decadal climate variability and
change.
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THE TEN CLIMATE MONITORING PRINCIPLES
The NRC (1999) report identified ten principles that should be applied to climate monitoring
systems. These principles are guiding the development of the CRN. They include:
(1)
Management of Network Change: Assess how and the extent to which a proposed change
in a climate observing network could influence the existing and future climatology obtainable
from the system, particularly with respect to climate variability and change.
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(2)
Parallel Testing: Make overlapping measurements to derive transfer functions for converting
between climatic data taken before and after a change in an existing observing system, or
taken from two parallel systems. The period of overlapping measurements should be
sufficiently long to observe the behavior of the two systems over the full range of variation of
the climate variable observed. The preferred minimum period of overlap is two consecutive
years.
(3)
Metadata are crucial. Fully document each observing system and its operating procedures.
This is particularly important immediately prior to and following any change.
(4)
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.
(5)
Integrated Environmental Assessment: Anticipate the use of data in the development of
environmental assessments, particularly those pertaining to climate variability and change, as
part of a climate observing systems strategic plan.
(6)
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.
(7)
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.
(8)
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.
(9)
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.
(10)
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, and quality control should be an integral part of data
management. International cooperation is critical for successful data management.
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The CRN is part of a multi-year NOAA climate initiative to create a network that meets the
GCOS standards (WMO, 1989) for long-term climate monitoring. The number of CRN stations that
can be deployed and the rate of deployment are dependent on the level of funding. The project was
supported at a level of 0.5 million dollars (U.S.) during its first fiscal year (FY 2000) and 3.5 million
dollars during FY 2001-02. Much of the effort during the first year was focused on developing
project specifications and requirements and testing and evaluating candidate instrumentation . The
first station pair was deployed in western North Carolina, near Asheville, in close proximity to both
NCDC and ATDD. The CRN instrumentation and data from these sites are being evaluated during
the second year of the project in a A proof of concept phase. During FY 2001-2 deployment will
begin for an additional 25 station pairs in locations across the U.S. representing a cross-section of
climatic zones.
REFERENCES
National Research Council (NRC), 1999: Adequacy of Climate Observing Systems, National
Academy Press, Washington, D.C.
IPCC (Intergovernmental Panel on Climatic Change), 2001: Climate Change 2001: The Scientific
Basis (Summary for Policymakers and Technical Summary of the Working Group I
Report). World Meteorological Organization, Geneva, Switzerland, 98 pp.
WMO (World Meteorological Organization), 1966: Climatic Change. Publication Technical Note
No. 79 (WMO-No. 195, TP. 100), Geneva, Switzerland, 79 pp.
WMO (World Meteorological Organization), 1986: Guidelines on the Selection of Reference
Climatological Stations (RCSs) from the Existing Climatological Station Network.
Publication WCP-116 (WMO/TD-No. 130), Geneva, Switzerland, 16 pp.
WMO (World Meteorological Organization), 1988: Technical Regulations. Volume I: General
Meteorological Standards and Recommended Practices. Publication No. 49, Geneva,
Switzerland.
WMO (World Meteorological Organization), 1989: Guide on the Global Observing System.
Publication No. 488, Geneva, Switzerland.
WMO (World Meteorological Organization), 1993: Report of the Experts Meeting on Reference
Climatological Stations (RCS) and National Climate Data Catalogues (NCC). Offenbauch
am Main, 25-27 August 1992. Publication WCDMP-No. 23 (WMO-TD No. 535). Geneva,
Switzerland, 94 pp.
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