Sometime in 1997, but definitely by January 18, 1998, the estimated average global temperature of 15 degrees Celsius (°C) was lowered to 14 degrees Celsius, which instantly made the average global temperature reach a “record high” of 14.40°C in 1997! [8]

NASA Goddard Institute’s director James “Jim” Hansen reported via email to Worldwatch this change, informing them 14°C was a “better base number” as documented in 2012 by American Thinker article “Fourteen is the New Fifteen].

Documents dated 1997, as reported in The American Thinker, that NASA quietly changed the “inconvenient” average global temperature of 15 degrees Celsius (°C) to a lower 14 degrees Celsius, as 15°C “did not support the allegations of global warming”. [1, 2, 3]

Prior to 1997, 15°C is documented as the average global temperature in multiple locations:

  • In March 1988 the New York Times quotes Hansen as stating that the “30-year period 1950-1980, when the average global temperature was 59 degrees Fahrenheit [15 degrees Celsius], as a base to determine temperature variations.” – the zero point! [1, 2, 3]
  • The first IPCC Assessment Report was released in 1990 which “underlined the importance of climate change as a challenge with global consequences and requiring international cooperation.”  On page xxxvii in the Table of this 1990 report it lists the “Observed Surface Temperature” of Earth as 15 degrees Celsius – see Table on page 37 (xxxvii),
  • and again in 1995 the IPCC Report on page 26 & 57 stated 15 degrees C. [5]

As reported in the 2012 American Thinker cited article, sometime in 1997 the average global temperature is stated to be lowered to 14°C, as shown in multiple locations, but JJanuary 18, 1998, NASA’s James Hansen changed the Goddard Institute’s estimated average global temperature from 15 degrees Celsius to 14 degrees Celsius

Today IPCC shows multiple graphs with a “zero point” but it is hard to find what temperature that point represents.

  • But the in March 2020 the “global mean surface air temperature for that [base] period [1951-1980] was estimated to be 14°C (57°F)” not 15 as Hansen claimed in 1988! [4]