According to the leaders of the global warming doomsday cult, the average surface temperature of Earth is 14 degrees Celsius (57.2 degrees Fahrenheit), but this is a new value which has quietly replaced the original average of 15 degrees Celsius (59 degrees Fahrenheit).

In March 1988, a few months before NASA's James Hansen asserted before the Congress that global warming was in progress, the New York Times quoted him as saying that he used 59 degrees Fahrenheit as the average global temperature to calculate the temperature variations.

One of the scientists, Dr. James E. Hansen of the National Aeronautics and Space Administration's Institute for Space Studies in Manhattan, said he used the 30-year period 1950-1980, when the average global temperature was 59 degrees Fahrenheit, as a base to determine temperature variations.

In July of the same year, a report in the Connecticut-based newspaper The Day was consistent with this claim.  According to the Day's report on Hansen's congressional testimony:

Dr. Hansen informed the lawmakers that the first five months of 1988 were the hottest five-month period on record, averaging four-tenths of a degree above a 30-year (1950-1980) norm of 59 degrees Fahrenheit.

Although Hansen's recent publications provide his version of the differences from the base temperature for various years, he is careful enough not to provide either the observed temperatures or the value of the baseline temperature.  However, Hansen at one time revealed his base value in an academic publication.  That paper, "Climate Impact of Increasing Atmospheric Carbon Dioxide," appeared in Science in August 1981 and states:

The mean surface temperature is Ts ~ 288 K.

Two hundred and eighty-eight K, or 288 Kelvin, is the same as 15 degrees Celsius.  A report in the Schenectady-based Daily Gazette indicates that Hansen and his colleague Helene Wilson used this value at least as late as 1992.  Thus, Hansen consistently used 15 degrees Celsius as the baseline average for several years.

James Hansen was not the only person to use this value.  When the Intergovernmental Panel on Climate Change (IPCC), which was set up soon after Hansen's 1988 testimony before the Congress, came out with its First Assessment Report in 1990, a table on page xxxvii of the report listed the "Observed Surface Temperature" of Earth as 15 degrees Celsius.

Yet another person who used 15 degrees Celsius as the global average temperature was Anthony J. McMichael, an activist professor whose e-mail promising to pull strings in the Australian government figured in the Climategate scandal.  According to McMichael's 1993 book, Planetary Overload: Global Environmental Change and the Health of the Human Species:

Average temperature over past 10,000 years = 15°C

As it turned out, the average temperature of 15 degrees Celsius was an inconvenient value that did not support the allegations of global warming.

In 1996, Michael Mann (who shot to fame during the Climategate scandal as the creator of "Mike's Nature trick" to "hide the decline") co-authored a paper titled "Greenhouse Warming and changes in the seasonal cycle of temperature: Model versus observations."  The paper pointed out that the predictions made by climate models were not consistent with observed data and the variability in temperature  likely resulted from natural phenomena.

... the signature of greenhouse warming is scarcely evident in the observational data[.] ... It is possible that observed trends in phase, largely influenced by mid-latitude continental interiors, do not arise from greenhouse warming, but rather from natural variability. Such a notion is reinforced by the fact that marginally-significant trends are found in the control GFDL annual cycle, presumably due to organized century-scale internal variability.

If, on the other hand, the observed variation in the seasonal cycle truly represents a "fingerprint" of greenhouse warming, the GFDL and CCM1 models do not appear capable of capturing the detailed responses of the seasonal cycle to greenhouse forcing.

...

Discrepancies between the observed and model-predicted trends must be resolved before a compelling connection can be drawn between 20^th century changes in the behavior of the annual cycle in temperature, and anthropogenic forcing of the climate.

Significantly, Mann used 15 degrees Celsius as the baseline temperature while calculating the parameters of the annual temperature cycle (see Figure 2 in his paper).  Although he could have picked any value in the cycle, he picked 15 degrees Celsius, and it is reasonable to assume that he did so because it was the accepted long-term global average temperature.

Not long after Mann's paper was published, the Worldwatch Institute, an organization based in Washington, D.C., came out with the 1997 edition of Vital Signs, its annual publication.  The publication had a chapter with the title "Global Temperature Down Slightly."

In literature published after the 1997 report by Worldwatch Institute, the leaders of the global warming movement seem to have started using 14 degrees Celsius for the global average temperature.  In 2002, the Sydney Morning Herald quoted James Hansen, who mentioned this new average.

This year the Earth's average temperature was 14.64C, compared with the long-term average of 14C, said James Hansen, of NASA's Goddard Institute for Space Studies, who analyses the data collected from thousands of weather stations around the world.

The IPCC too now uses 14 degrees Celsius as its base temperature, as can be seen from a graph that is part of its 2007 document.  (As an aside, it was in 2007 that IPCC won the Nobel Peace Prize.  IPCC certainly deserved a Nobel Prize, but it should have been for literature, as the organization had excelled in writing fantasy.)

More recently, a 2011 report by the Government Accountability Office attributes an estimated average surface air temperature of 287 K, or 14 degrees Celsius, to James Hansen and his colleagues.

But Hansen and colleagues have estimated that Earth's actual average surface air temperature between 1951 and 1980 was approximately 287 K (14 degrees Celsius) (Hansen et al. 2010).

It is hard to pinpoint the exact date when the change from 15 degrees to 14 degrees was introduced.  It most likely happened sometime in 1997, and definitely no later than January of 1998.

The 1998 edition of the annual publication of Worldwatch Institute uses 14 degrees Celsius as the global average temperature and provides details of how it was informed of the change from 15 degrees Celsius.  On page 69 of the report, a footnote below the table listing the global average temperatures for several years states:

Base number is 1 degree Celsius lower than in earlier Vital Signs.

On page 174 of the same report, we see the explanation for the change.

In earlier versions of Vital Signs, Worldwatch added the temperature change reported by the Goddard Institute to an estimated global temperature of 15 degrees Celsius, but the institute has since informed Worldwatch that a better base number would be 14 degrees Celsius. James Hansen, Goddard Institute for Space Studies, New York, email to author, 18 January 1998.

In other words, James Hansen sent word that 14 is the new 15.

The author can be reached at arvind [at] classical-liberal [dot] net.