The NWS operates and maintains many of the nation's weather and climate observing systems. Climate station standards are generally stricter than weather station standards because both data accuracy and long-term consistency are critical. It is not cost effective to have separate systems so we must ensure that all data needs are met with the existing networks.

Some climatologists argue that continuity is as important, if not more important, than absolute accuracy, for tracking the time-dependent behavior of climate, including trends and variability, and for assessment and analysis of extreme values and climatic risk factors. In any case, climate data form the basic building blocks for a multitude of applications, including the sciences of meteorology and climatology.

In recent decades, the observing systems were operated on the premise that the NWS's primary mission of forecasts and warnings for the protection of life and property was the paramount driver. However, as the numerous applications of the data outside the NWS continue to grow and NOAA became the government's lead agency for monitoring and assessing climate variability and change, it became mandatory that NWS refocus its management policies to include the somewhat forgotten climate needs of the systems.

The purpose of long-term (decades or longer) climate monitoring systems is to deliver continuous and reliable data and information. The data serve a great variety of climate services applications, including describing the climate, monitoring climate variability, climate change detection, national economic development, supporting climate research, modeling, and prediction, and mitigation of impacts.

Climate data are also used in a multitude of socio-economic decision-making activities, ranging from sizing dam spillways and storm drains for runoff to the slope on highways to insure adequate water runoff, to the depth needed for structural foundations to ensure long-term building stability. Industry uses weather and climate data in near real-time to understand business and sales trends (socio-economic indices). These applications all require measurements that are made in a consistent manner for long time periods.

Climate observations made under the oversight of the National Weather Service constitute the principal lasting legacy of the agency for future generations (NWS Director Jack Kelly, 2003). While forecasts and warnings have a short shelf life, climate data lasts centuries and longer. The data are as much a part of the national heritage as are material artifacts housed in the Smithsonian Museum in Washington D.C.

Climate observations will be examined repeatedly and in fine detail by advanced computers and algorithms for years, decades, and centuries to come. Diligent efforts must be made to insure that these observations are adequately and correctly documented and archived as they are meant to represent the true state of the atmosphere at the point of their measurement. In many ways, the NWS will be judged by the quality of the records it leaves to posterity.

NOAA/NWS is indeed viewed as the nation's "neutral brokers" or stewards, for environmental data. For many legal applications such as contracts and litigation, NOAA data are the only source of information accepted for use.

In recent decades, another critical application of climate data has developed, its use in assessing global warming (greenhouse warming). Figure 4 illustrates the uncertainty (9 degrees F) associated with various greenhouse warming senarios according to a recent Intergovernmental Panel on Climate Change (IPCC). Note that the projected changes are comparable to the error of a single observation, illustrating the importance of strict adherence to siting and sensor standards.

Glocal Temperature rise versus year with envelope of projected global surface temperature
Figure 4. Simulated Climate Responses for a Range of Emission Scenarios.

NOAA is now the nation's federal lead for climate services, including climate change research. We must recognize and respect the importance of NOAA's climate monitoring mission, be aware of factors that can degrade the accuracy and continuity of that record, and exercise prudent judgment to minimize the unwanted uncertainty these factors introduce into our datasets. Doing so will increase the quality of our climate databases and support efforts to better understand what is happening to our climate.

Numerous factors can introduce uncertainty into the climate record. Some, such as instrument change, cannot be avoided. Sensors need replacement when they reach the end of their life cycle. Ongoing environmental change also cannot be totally avoided. Trees grow and landscapes change. Under these circumstances, the best we can do is document the change through accurate metadata (data about data). To the many, the exposure changes that affect the measured climate may be invisible or appear subtle, dull and uninteresting as they happen but they nonetheless add some level of uncertainty to our climate record.

Figure 5 is the much publicized global temperature record. It illustrates the importance of accuracy in climate data and assessments. Note that climate trends are being evaluated to the nearest tenth of a degree Fahrenheit (F) over decades and centuries. The great global debate over the magnitude and causes of this warming are centered around potentially hundreds of billions of dollars of socio-economic action in just the U.S (United States Congress, Office of Technology and Assessments, 1991). The global implications are even greater.

Decision-makers need the most accurate data and assessments available to assist them in evaluating options for mitigation. Accurate, consistent, well understood data minimize the risk of making wrong, costly decisions and maximize the socio-economic benefit of action.

Time series of departures in global temperature from thermometers data.
Figure 5. Time series for 140 years of global land temperature departure from climatology (1961-1990).