In the IPCC’s 2001 third report (TAR), the total surface temperature increase for the 20th century was reported to be “about 0.6¬∞C”.
“The global average surface temperature has increased over the 20th century by about 0.6¬∞C.”
This Met Office graph of global temperatures for 1860-2000 was included in the IPCC’s 2001 report. It provided visual clarification of the 0.6¬∞C temperature increase since 1900.
In taking a closer look, the graph does indeed show a warming of 0.6¬∞C between 1900 and 2000:
At the time, this warming amplitude for the 20th century was widely accepted in the scientific literature. For example:
“Humans may be responsible for less than 0.01¬∞C (of approximately 0.56¬∞C (1¬∞F) total average atmospheric heating during the last century).”
“The global average surface temperature has increased by about 0.6¬∞C over the twentieth century.”
“An analysis of observational records shows that the global surface air temperature (SAT) has increased by 0.6¬∞C since 1861.”
The IPCC Adds 0.3¬∞C Of Phantom Warming To Global Temperatures Between 2001 and 2013 Reports
The IPCC authors acknowledged that there was a pause in global warming since the 21st century began in the 2013 report (AR5), regularly referring to the pause as a “hiatus.” They even acknowledged that 97% of climate model simulations (111 of 114) got it wrong, or didn’t simulate the lack of warming:
IPCC AR5 Chapter 9 (2013):
“For the period 1998‚Äì2012, 111 of the 114 climate-model simulations show a surface-warming trend larger than the observations.”
“Almost all CMIP5 historical simulations do not reproduce the observed recent warming hiatus.”
Even the UK’s Met Office — where the IPCC obtains temperature data (HadCRUT) — acknowledged there was a pause in global warming since the early 2000s in a paper published in July, 2013, entitled “The Recent Pause in Global Warming.”
“The start of the current pause is difficult to determine precisely. Although 1998 is often quoted as the start of the current pause, this was an exceptionally warm year because of the largest El Ni√±o in the instrumental record. This was followed by a strong La Ni√±a event and a fall in global surface temperature of around 0.2oC (Figure 1), equivalent in magnitude to the average decadal warming trend in recent decades. It is only really since 2000 that the rise in global surface temperatures has paused.”
Nonetheless, by the time the 5th report (AR5) was released later that year (2013), the IPCC (and the Met Office) had decided that a substantial warming of 0.25¬∞C had occurred since the release of the 2001 report. Twelve years and a hiatus later, the 0.6¬∞C of warming since the 19th century ended had been transformed into 0.85¬∞C of warming.