In November 1993 “Anthony J. McMichael, an activist professor whose e-mail promising to pull strings in the Australian government figured in the Climategate scandal”, published his book Planetary Overload: Global Environmental Change and the Health of the Human Species, where he documented the average global temperature as 15 degrees celsius. This appears to be the last time this 10,000 year average figure was published. [1]
“As it turned out, the average temperature of 15 degrees Celsius was an inconvenient value that did not support the allegations of global warming.” On January 18, 1998, James Hansen, via an email to Worldwatch Institute, “the leaders of the global warming movement” told them that a “better base number” would be 14 degrees C. Around this time a zero point started to appear in the graphs, and has done since in IPCC reports. [2, 3]
“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.” [1]
Climate Change timeline – EXPLORE