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 1998–2012, 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 Niño in the instrumental record. This was followed by a strong La Niña 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.
“The globally averaged combined land and ocean surface temperature data as calculated by a linear trend show a warming of 0.85°C over the period 1880 to 2012.“
Apparently, 0.6°C since 1900 wasn’t substantial enough. So 0.25°C of additional warming was tacked on. After all, 0.85°C sounds a lot more dangerous than 0.6°C.
But notice there was a difference in starting points here: 1880 vs. 1900. Was it possible that 1880 was -0.25°C cooler than 1900, which would account for the discrepancy? Not according to the IPCC’s own 1860-2000 graph from the 2001 report. Both 1880 and 1900 temperature anomalies were identical, as seen here:
So was it possible the additional 0.25°C of warming occurred since the 21st century began, or since 2001? Not according to the HadCRUT temperature dataset. Version HadCRUT3 was in use through 2012, and according to the data made available for public use on WoodForTrees.org (green trend line), HadCRUT3 indicated there was a cooling of about -0.05°C between 2001 and 2012. The advent of HadCRUT4 in late 2012 allowed the Met Office to make substantial “up-justments” to the recent data, especially for the 2005 – 2012 period. This extra warming added to the data could potentially eliminate the pause, or better conform temperatures to climate model expectations. But even those “up-justments” didn’t work. There was still no warming trend for the 2001-2012 period (purple trend line) even with the “up-justed” temperatures for HadCRUT4 from HadCRUT3.
So with the elimination of the -0.05°C cooling between 2001 and 2012 as indicated by the HadCRUT3 data, and with the addition of 0.25°C of extra warming since 1880 or 1900 that didn’t exist in the 2001 report, the IPCC and the Met Office were able to subtly add 0.3°C to global temperatures between their 3rd and 5th reports.
But perhaps a more recent graph (2015) might shed light on where this extra 0.3°C of warming could possibly be coming from. It doesn’t.
Adapted Met Office graph available here.
Other than more-of-the-same suppression of the 1880s to 1940s warming period (notice the 1940-’45 warming amplitude has recently been reduced by -0.05°C, making 1980 warmer), the warming trend for the 20th century (1900-2000) is still 0.6°C as shown on this 2015 Met Office graph. And between 1880 and 2012, the graph still shows 0.6°C of warming (actually, about 0.55°C, since 1880 has recently been heated up almost 0.1°C relative to 1900 for some reason). Neither starting point (1880 or 1900) indicates a warming amplitude of 0.85°C as claimed by the IPCC in 2013.
Met Office Has Removed 0.3°C Of Global Warming Amplitude From 1880s-1940s Period, And Transformed Strong 1940s-’70s Cooling Into A Pause
As just mentioned, the most recent depictions of the global warming trend for the 20th century have 1980 about 0.05°C warmer than 1940-’45. A few decades ago, or before a series of chronic “adjustments” to the data were made to artificially reduce the 1940s warming height, 1980 was still about -0.15°C cooler than 1940-’45, a net change of 0.2°C.
For example, this 1981 global temperature graph from NASA shows 1940 still 0.15°C warmer than 1980. James Hansen, lead author of the paper, even admitted that he thought it was “remarkable” that 1980 is almost as warm as 1940 was.
“A remarkable conclusion from Fig. 3 [below] is that the global mean temperature is almost as high today  as it was in 1940.”
Reducing the 1920s to 1940s warming amplitude has apparently been a high priority agenda item for overseers of temperature datasets for quite some time. In exposed e-mail exchanges from 2009, for example, Phil Jones and Tom Wigley — both overseers of the HadCRUT datasets spanning decades and activists for the anthropogenic global warming cause — discuss reducing the “1940 blip” in their reconstructions of 20th century temperatures by simply cooling the 1940 temperature data down by -0.15°C.
“If you look at the attached plot you will see that the land also shows the 1940s blip (as I’m sure you know). So, if we could reduce the ocean blip by, say, 0.15 degC, then this would be significant for the global mean — but we’d still have to explain the land blip. I’ve chosen 0.15 here deliberately. This still leaves an ocean blip, and i think one needs to have some form of ocean blip to explain the land blip (via either some common forcing, or ocean forcing land, or vice versa, or all of these). When you look at other blips, the land blips are 1.5 to 2 times (roughly) the ocean blips — higher sensitivity plus thermal inertia effects. My 0.15 adjustment leaves things consistent with this, so you can see where I am coming from. Removing ENSO does not affect this. It would be good to remove at least part of the 1940s blip, but we are still left with “why the blip”.
— Tom Wigley, Phil Jones exchange, from uncovered Climate Research Unit e-mails
Not only has reducing the amplitude of the 1920s to 1940s warming been a priority among dataset procurers for the sake of advancing the cause, so too has eliminating the 1940s to 1970s global cooling period from the temperature record. As shown in the Met Office graphs above, the 1940 to 1970 global cooling period extensively referenced in the scientific literature has now been reduced to a mere fraction of what it was reported to be during the 1970s.
The warming amplitude for the 1880 to 1940 period has now been reduced to between 0.2° and 0.3°C in modern datasets (see the smoothed blue trend line from 2015 Met Office graph above). The cooling period between 1940 and 1970 has now been reduced to less than 0.1°C.
During the 1970s, it was commonly accepted by climatologists that the Earth had warmed by about +0.6°C between 1880 and 1940, and then cooled by -0.3°C between 1940 and 1970 (before temperatures began rising again in the late 1970s). The Southern Hemisphere experienced only modest warming and cooling, but in the Northern Hemisphere, the warming and cooling was especially pronounced: 1°C of warming from 1880 to 1940, and -0.5°C cooling from 1940 to 1970. Below are some examples of the widely accepted global and Northern Hemisphere temperature trends mentioned in the scientific literature during the 1970s.
“[B]etween 1880 and 1940 a net warming of about 0.6°C occurred, and from 1940 to the present our globe experienced a net cooling of 0.3°C.”
“In the period from 1880 to 1940, the mean temperature of the earth increased about 0.6°C; from 1940 to 1970, it decreased by 0.3-0.4°C.”
Introduction: “In the last century it is possible to document an increase of about 0.6°C in the mean global temperature between 1880 and 1940 and a subsequent fall of temperature by about 0.3°C since 1940. In the polar regions north of 70° latitude the decrease in temperature in the past decade alone has been about 1°C.”
“Instrumental surface temperature records have been compiled for large portions of the globe for about the past 100 years (Mitchell, 1961; Budyko, 1969). They show that the Northern Hemisphere annual mean temperature has risen about 1°C from 1880 to about 1940 and has fallen about 0.5 °C since then”
“[A]verage temperature data for the northern hemisphere shows the range of change between 1880 to 1940 to be approximately 1.1°C.”
“Since 1940, however, the temperature of the Northern Hemisphere has been steadily falling: Having risen about 1.1 degrees C. between 1885 and 1940, according to one estimation, the temperature has already fallen back some 0.6 degrees, and shows no signs of reversal.”
The net effect of substantially removing the warming from the 1880 to 1940 period (and concomitantly adding warming to the 1940s to 1970s cooling period) is to make the warming trend for the 20th and 21st centuries appear linear rather than oscillatory. A linear warming fits climate models better, as the CO2 emissions rates have been linearly rising, of course, especially after about 1950. Making the temperature record conform to modeling of CO2-induced climate changes is the main agenda.
Observations Found In Scientific Papers Reveal A 20th Century Temperature Oscillation, Not Linear Warming
If we were to return the 0.3°C of warming observed during the 1880s to 1940s period removed by the Met Office over decades of “adjustments” to the data, the graph of surface temperature changes might look like this:
Interestingly, when scientists reconstruct surface and ocean temperatures for the 20th century using physical evidence (such as ice cores), the steepness of the warming and cooling trends for the pre-1970s era looks eerily similar to the oscillatory trends depicted above. In other words, modern scientists who have been recently eliminating the warming amplitude of the 1880s to 1940s period to conform to CO2-centered climate modeling would appear to be making the datasets less accurate than they were in the 1970s … and all for the sake of an agenda.
Below are several examples of an oscillatory rather than linear temperature record for the 20th century (i.e., pronounced cooling after the 1940s and a decelerated warming since the 1970s) found in the peer-reviewed scientific literature.
“The annual whole ice sheet 1919–32 warming trend is 33% greater in magnitude than the 1994–2007 warming.”