Last summer’s headlines blared, “Hottest July in the history of the United States.” The National Climatic Data Center (NCDC) of the U.S. National Oceanic and Atmospheric Administration (NOAA) said so, so it must be true.
This week, the NCDC is reporting the same, with the added alarm that 2012 was the warmest year on record and one of the top two years for extreme weather in America.
Climate activists are linking this to man-made global warming, ignoring the fact that the area covered in the NCDC reports, the contiguous United States (excluding Alaska), comprises only 2 percent of the Earth’s surface. Trends that may manifest in the United States in no way indicate global phenomena. In fact, the United Kingdom’s Meteorological Office has said that there has been no global warming for 16 years and this week announced that temperatures are expected to stay relatively stable for another five years.
Regardless, all NCDC temperature proclamations must be taken with a large grain of salt. Here’s why.
Until the use of thermocouple temperature indicators became common in the U.S. climate network, temperatures were determined with mercury thermometers that are, at best, only accurate within 0.9 degree Fahrenheit. Even today, many U.S. stations only record temperatures to the closest whole degree. Thus, breaking the 1936 high temperature record by 0.2 degrees F, as NCDC claimed occurred last July, is not meaningful. This change falls within the uncertainty of the measurement. It is akin to being alarmed that the moon has moved a millimeter closer when we can only measure the Earth-moon distance to within a few centimeters.
All that was recorded for most of the United States was minimum and maximum temperature for each day. The NCDC’s so-called average daily temperatures were derived by simply computing the average of the minimum and maximum temperatures. This is not a true average, however, since it does not take into account how temperatures varied throughout the day.
Trusting the NCDC averaging method to reach “hottest ever” conclusions is a mistake, because higher minimums at night will yield a higher daily average, even if daytime highs do not rise.
This is what happened in July 2012. Then, NCDC records indicated that the United States was less cool at night than in July 1936, therefore, the average they computed for July 2012 was higher than in 1936. Yet, Roy Spencer of the University of Alabama at Huntsville demonstrated that NCDC records show daytime high temperatures in July 1936 far surpassed those of 2012. July 2012 was not the warmest month in the American 118-year instrumental record.
This week, NCDC’s credibility was further damaged when meteorologist Anthony Watts of Chico, Calif., announced that he had discovered huge differences between their “State of the Climate” (SOTC) reports released each month and the actual database of NCDC temperatures. For example, the July 2012 SOTC report, issued in early August, announced that a new record had been set with the average July temperature for the contiguous United States at 77.6 degrees, one-fifth of a degree higher than in July 1936. However, the NCDC now says the July 2012 average was actually about 76.9 degrees, nearly 0.7 degrees less. This is almost 0.5 degrees cooler than the 77.4 degrees claimed as the previous monthly record in 1936. What is going on?
It turns out that the NCDC does not wait for all the data to be received before computing and very publicly announcing the U.S. average temperature and its rank compared to other months and years. While some stations, such as those at airports, send the data quickly via radio links and the Internet, other stations use old paper forms that arrive by mail considerably later.
When the printed data finally arrive, the NCDC updates its temperature database, typically “cooling” the country when all the data are used.
Neither the NCDC nor NOAA tells the public and the press that the temperature announcements in previous SOTCs are no longer correct when the complete data set is analyzed.
Strangely, NCDC changes temperature data even from the distant past without notification. For example, NCDC now asserts that the average temperature in July 1936 was 76.4 degrees, a full degree cooler than the 77.4 degrees that they claimed for the month in the July 2012 SOTC report. This allows them to continue to say that July 2012 set a record.
Mr. Watts found that in the 23 monthly SOTC reports between October 2010 and November 2012 (three SOTC reports did not list average temperatures), 22 of them do not match the NCDC database, presumably due to later updating when all the data are received and analyzed. In all cases except one, the country cooled when all the data were incorporated.
Mr. Watts concludes: “It is mind-boggling that this national average temperature and ranking is presented to the public and to the press as factual information and claims each month in the SOTC, when in fact the numbers change later.”


We don’t really know how much, if any, warming has occurred in the United States over the past century. Since the American record is considered to be the most accurate part of the Global Historical Climatology Network, we really don’t even know that global warming has occurred at all in the past century.