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NCDC Introduces the National Temperature Index Page

Graph comparing annual national temperature anomalies from the nClimDiv and USCRN datasets

Comparison of annual national anomalies for the nClimDiv (solid) and USCRN (dashed) maximum (red), mean (green), and minimum (blue) temperatures.

NCDC developed the U.S. Climate Reference Network (USCRN) to address the most basic of climate change questions that Americans will ask in the mid-21st century, “How has the climate of the Nation changed in the last 50 years?” The USCRN measures temperature with superior accuracy and continuity in places that land-use change will not likely impact during the next five decades. Built specifically for this purpose, it is unlike any other climate observation network in the United States. NCDC began the USCRN build-out in the lower 48 states in 2000 and completed the last of 114 station installations in 2008. Since 2005, the USCRN has operated a sufficient number of stations to generate accurate annual national temperature averages.

The USCRN serves, as its name and original intent imply, as a reference network for operational estimates of national-scale temperature. NCDC builds its current operational contiguous U.S. (CONUS) temperature from a divisional dataset based on 5-km resolution gridded temperature data. This dataset, called nClimDiv, replaced the previous operational dataset, the U.S. Historical Climatology Network (USHCN), in March 2014. Compared to USHCN, nClimDiv uses a much larger set of stations—over 10,000—and a different computational approach known as climatologically aided interpolation, which helps address topographic variability. However, nClimDiv preserves USHCN’s groundbreaking methods to detect and correct station biases brought on by changes to the station network over time.

In 2013, to help users compare the performance of the current and former operational CONUS temperature datasets, NCDC developed a National Temperature Index page. The page presents the CONUS temperature values using the 1981–2010 average as a common base period. This is exactly what NCDC designed the USCRN to do: serve as a highest-quality reference for observations through the first half of the 21st century. The National Temperature Index page demonstrates that the operational CONUS temperature datasets—nClimDiv and USHCN before it—are capable of accurately measuring U.S. surface air temperature. Having comparative sets of data is the best of all worlds and provides ongoing verification of the temperature changes in the United States during the coming century. As the overlap period between the networks lengthens over time, the continued close agreement of the independent measurements of U.S. temperature also serves to confirm that the procedures used to correct operational network stations undergoing change over time are successful. This further validates the 20th century record of U.S. temperature based on these operational networks and methods.

Visit the National Temperature Index page on NCDC’s website.