Uncovered: Incoherent, Conflicting IPCC ‘Beliefs’ on Climate Sensitivity

For going on 3 decades now, Intergovernmental Panel on Climate Change (IPCC) reports have estimated that the climate’s sensitivity to the doubling of preindustrial levels of CO2 (from 280 ppm to 560 ppm) may range between 1.5°C to 4.5°C due significantly to the assumed “dangerous” warming amplification from positive water vapor feedback.  Despite years of analysis, the factor-of-three difference between the lower and higher surface temperature range thresholds has changed little.  There apparently have been no breakthroughs in understanding the “basic physics” of water vapor amplification to narrow this range further.

The theoretical conceptualization for the surface temperature change resulting from CO2 doubling alone — without the “dangerous” amplification from  water vapor feedback — has also been in use, and unchanged, for decades.  Since the 1960s it has been hypothesized that if preindustrial CO2 levels were to be doubled to 560 ppm, the surface temperature change would amount to a warming of a non-alarming 1.2°C in the absence of other feedbacks.

Below are brief summaries from scientific papers (and the Skeptical Science blog) confirming that the IPCC and models claim doubling CO2 only results in 1.2°C of warming.

IPCC (2001) :

“[T]he radiative forcing corresponding to a doubling of the CO2 concentration would be 4 Wm-2. To counteract this imbalance, the temperature of the surface-troposphere system would have to increase by 1.2°C (with an accuracy of ±10%), in the absence of other changes”

Skeptical Science :

“We know that if the amount of carbon dioxide (CO2) in the Earth’s atmosphere doubles from the pre-industrial level of 280 parts per million  by volume (ppmv) to 560 ppmv, this will cause an energy imbalance by trapping more outgoing thermal radiation in the atmosphere, enough to directly warm the surface approximately 1.2°C.”

Gebhart, 1967 :

“The temperature change at the earth’s surface is ΔT=+1.2°C when the present [CO2] concentration is doubled.”

Hansen et al., 1981 :

“The increase of equilibrium surface temperature for doubled atmospheric CO2 is ∼1.2°C.  This case is of special interest because it is the purely radiative-convective result, with no feedback effects.”

Lorius et al., 1990 :

“The radiative forcing resulting from doubled atmospheric CO2 would increase the surface and tropospheric temperature by  1.2°C if there were no feedbacks in the climate system.”

Torn and Harte, 2006 :

“An increase in atmospheric CO2 concentration from 275 to 550 ppm is expected to increase radiative forcing by about 4 W m2, which would lead to a direct warming of 1.2°C in the absence of feedbacks or other responses of the climate system”


IPCC: Dangerous future warming levels (3°C and up) are caused mostly by water vapor, not CO2

As mentioned, the IPCC authors have claimed that it is primarily due to the conceptualization of positive feedback with water vapor that the surface temperature response is projected  to reach the dangerous warming levels of 3.0°C and up as CO2 doubles to 560 ppm.

IPCC (2001) :

“The so-called water vapour feedback, caused by an increase in atmospheric water vapour due to a temperature increase, is the most important feedback responsible for the amplification of the temperature increase [from CO2 alone].”

In their 4th report, the IPCC acknowledged that humans have little influence in determining water vapor levels:

IPCC (2007) :

“Water vapour is the most abundant and important greenhouse gas in the atmosphere. However, human activities have only a small direct influence on the amount of atmospheric water vapour.”

The main reason why IPCC authors have asserted that water vapor will do most of the “dangerous” projected warming, while CO2 will contribute a much smaller fraction, is apparently because the greenhouse warming effect from water vapor forcing is “two to three times greater” than that of carbon dioxide:

IPCC (2013) :

“Water vapour is the primary greenhouse gas in the Earth’s atmosphere. The contribution of water vapour to the natural greenhouse effect relative to that of carbon dioxide (CO2) depends on the accounting method, but can be considered to be approximately two to three times greater.”

Even NASA agrees that water vapor and clouds together account for 75% of the greenhouse effect, while CO2 only accounts for 20%.


Carbon dioxide causes about 20 percent of Earth’s greenhouse effect; water vapor accounts for about 50 percent; and clouds account for 25 percent. The rest is caused by small particles (aerosols) and minor greenhouse gases like methane.”


IPCC: Positive water vapor feedbacks are believed to cause dangerous warming

It is curious to note that the insufficiently understood positive water vapor feedback conceptualization is rooted in . . . belief.  Literally.   In the third report (TAR), the IPCC authors actually used the word “believed” to denote how they reached the conclusion that 1.2°C will somehow morph into 1.5°C to 4.5°C of warming due to amplification from feedbacks.

IPCC (2001) :

“If the amount of carbon dioxide were doubled instantaneously, with everything else remaining the same, the outgoing infrared radiation would be reduced by about 4 Wm-2. In other words, the radiative forcing corresponding to a doubling of the CO2 concentration would be 4 Wm-2. To counteract this imbalance, the temperature of the surface-troposphere system would have to increase by 1.2°C (with an accuracy of ±10%), in the absence of other changes. In reality, due to feedbacks, the response of the climate system is much more complex. It is believed that the overall effect of the feedbacks amplifies the temperature increase to 1.5 to 4.5°C. A significant part of this uncertainty range arises from our limited knowledge of clouds and their interactions with radiation.”

IPCC climate sensitivity estimates have been based on hypotheticals, or the belief that water vapor positive feedback will cause another 1.8°C to 3.3°C of “extra” or “dangerous” warming (to reach upwards of 3.0°C to 4.5°C).  CO2 alone only causes 1.2°C of warming as it is doubled from 280 ppm to 560 ppm.  Since when are modeled beliefs about what may possibly happen to global temperatures at some point in the next 100 years . . . science?

IPCC: Water vapor increased substantially since 1970 — but didn’t cause warming

If water vapor is the primary determinant of the “extra” and “dangerous” warming we are expected to get along with the modest 1.2°C temperature increase as the CO2 concentration reaches 560 ppm, then it is natural to ask: How much of the warming since 1950 has been caused by the additional CO2, and how much has been caused by the water vapor feedback that is believed to cause the extra, “dangerous” warming?

This last question arises because, according to the IPCC, there has been a substantial increase in the potent water vapor greenhouse gas concentration in the last few decades.  Specifically, in their 4th report, the IPCC authors claim there has been “an overall increase in water vapour of order 5% over the 20th century and about 4% since 1970“(IPCC [2007]).

Considering its abundance in the atmosphere (~40,000 ppm in the tropics), if water vapor increased by 4% since 1970, that means that water vapor concentrations could potentially have increased by more than 1,500 ppm in the last few decades.  The overall magnitude of this water vapor concentration increase is therefore more than 20 times greater than the increase in atmospheric CO2 concentration (~70 ppm) since 1970.

But even though the IPCC claims that (a) water vapor will cause most of the “dangerous” warming in the future, (b) water vapor climate forcing is “two to three” times greater than CO2 forcing within the greenhouse effect, and (c) water vapor concentrations have increased substantially since 1970, the IPCC simultaneously claims that (d) CO2 has caused most — if not all — of the warming since the mid-20th century anyway.   In the 5th report, the IPCC’s “consensus” statement reads like this:

IPCC (2013, 2014) :

“It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together.”

For advocates of dangerous anthropogenic global warming (DAGW) projections, the “more than half” CO2 attribution apparently isn’t quantitatively strong enough.  After all, “more than half” could be interpreted as only slightly more than 50%.   To rectify this, Gavin Schmidt  — a primary overseer of NASA temperature adjustments — has calculated that the anthropogenic impact on climate has not  just been “more than half,” but more than 100%.   In a recent RealClimate blog entry, Schmidt  claims that humans have caused 110% of the global warming since 1950 — and that IPCC analysis (found in Fig. 10.5 in IPCC AR5) also supports an anthropogenic CO2 attribution of  “near 100%”.

Real Climate :

“The best estimate of the warming due to anthropogenic forcings (ANT) is the orange bar [in Fig. 10.5] (noting the 1𝛔 uncertainties). Reading off the graph, it is 0.7±0.2ºC (5-95%) with the observed warming 0.65±0.06 (5-95%). The attribution then follows as having a mean of ~110%, with a 5-95% range of 80–130%. This easily justifies the IPCC claims of having a mean near 100%, and a very low likelihood of the attribution being less than 50% (p < 0.0001!).”


Conflicting IPCC climate sensitivity feedback suppositions

The IPCC believes that the climate’s overall surface temperature sensitivity to the doubling of preindustrial CO2 ranges between 1.5°C to 4.5°C, with the projected higher warming levels due primarily to amplifying water vapor feedback.  This conceptualization appears to be in conflict with other IPCC suppositions.

On one hand, the IPCC reports have claimed that (a) water vapor is much more potent than CO2 within the greenhouse effect, that (b) the bulk of the 3.0°C and up “dangerous” warming that is believed to occur in the future will be forced by positive water vapor feedback, and that (c) water vapor  levels have significantly increased in recent decades (by 4% since 1970).

On the other hand, (d) water vapor is claimed to have caused right around 0% of the warming in the last several decades.

Summarily, these conflicting explanations or suppositions about what can happen, what will happen, and what has already happened to the climate due to water vapor feedback beg the questions:

Why hasn’t the “dangerous” water vapor warming found in models “kicked in” during the last several decades, when water vapor levels have increased (according to the IPCC)? 

Since it reportedly hasn’t yet, at what point in the future will the “dangerous” water vapor warming projections found in modeling finally show up in the temperature record?

Considering how fundamental climate sensitivity estimates are to climate science, and ultimately to the direction of political policies and energy production and consumption, these questions deserve to be answered . . . with something more substantive than what the IPCC authors have long believed to be true. 

14 responses to “Uncovered: Incoherent, Conflicting IPCC ‘Beliefs’ on Climate Sensitivity”

  1. gallopingcamel

    There is an impressive correlation between CO2 and temperature that is backed up by hard science such as the EPICA ice cores. If you don’t know about this it is because it shows the exact opposite of what the IPCC claims:

    So EPICA researchers like Thomas F. Stocker know the truth yet they choose to lie about the CO2/temperature relationship. Maybe that is a condition of employment at the IPCC (Stocker’s employer).

    That is how the new soft Lysenkoism works……you go along to get along:

  2. John F. Hultquist

    This reminds me of early efforts to determine the age of Earth.

    … 1890s that the Irish geologist John Joly computed an age of about 80-90 Million years using Halley’s method …” (ocean salt concentration)

    There is a Richard Feynman talk about researcher’s bias while estimating one of the physical constants. One of the early and respected authorities said it was “X” so that’s what others used. But things didn’t work out using “X” so someone adjusted it a little. Someone else adjusted it a little more. Repeat. Eventually, the right answer was reached.

    In climate work, the 1.5°C to 4.5°C range meets the political alarm needs, while 1.2°C does not, and we don’t know if that is correct (close). Where did it first come from? Is it a calculation based on lab experiments, or is it a real-atmosphere measurement?

    1. Kenneth Richard

      It’s a basic radiative forcing theoretical climate model, not based on direct observational evidence. Since the ocean heats the atmosphere, and not the other way around (predominantly), it assumes that atmospheric CO2 can heat or cool the depths of the ocean when it is increased or decreased in volumes of parts per million (0.000001), which, again, has not been observed or subjected to a falsifiable physical scientific experiment. Some may say it’s “basic physics”, but that would imply we have observational, experimental evidence and physical measurements of cause-effect. We don’t.

      Here is a summary of the model’s basics:

      “This post is for the independent thinkers, the brains that want to know exactly where the famous, core, 1.2 °C figure comes from.”

    2. gallopingcamel

      The idea of a logarithmic relationship between [CO2] and temperature is false so you should not be surprised that nobody can say what the “Sensitivity Constant” is. In a nutshell, the 1896 Arrhenius theory is wrong because it does not explain what is observed.

      The IPCC picked 1850 as their start date because it appeared that temperature was following the CO2 concentration after that date. However global average temperatures fell from 1930 to 1975 even though the concentration of CO2 rose. Since 1998 the average global temperature has flat lined even though the rate of increase in CO2 concentration has accelerated. This proves that CO2 is at best a minor contributor to global warming.

      1. Mindert Eiting

        Just a small remark. The sensitivity is defined as temperature increase per doubling of the relative amount of a certain molecule. It reminds me of confused studies in which a small percentage is multiplied with some number (exceeding 1), which must with repeated application, produce percentages of more than one hundred percent. Should we assume here that doubling (times 2, 2^2, 2^3, …) will finally give the earth an atmosphere with more mass than the planet has? A formula with absurd consequences cannot work, even if proportions are initially one millionth.

      2. Arrhenius' Ghost

        Galloping Camel.

        That’s all correct regarding the 1896 work but Arrhenius corrected those errors in 1906 as published in: Arrhenius, S., 1906, Die vermutliche Ursache der Klimaschwankungen. Meddelanden från K. Vetenskapsakademiens Nobelinstitut 1: 2, 1ff.

        He concluded that:

        “Likewise, I calculate that a halving or doubling of the CO2 concentration would be equivalent to changes of temperature of –1.5 °C or +1.6° C respectively.”

        Now, that +1.6°C is an interesting figure. If you do a simple bit of arithmetic you will see he was not too far out:

        CO2 concentration 1906 = 280ppm.

        400 ppm (2016) – 280 ppm = 120ppm

        120/280 = 0.43

        0.43 x 1.6 C° = 0.69 C°.

        Actual temp increase 1905-2005 = 0.74 ± 0.2 C° (IPCC)

        1. yonason

          “Arrhenius corrected those errors in 1906” – Arrhenius’ Ghost

          Saying he “corrected” his previous error gives the impression that there is no longer a problem with his conclusion. That’s a bit misleading, as is using any IPCC agreement in support of it.

          Also, since correlation is not causation, just because the avg temp of the world went up a bit doesn’t automatically implicate CO2 as the cause. The nearly 2 decade long “pause” in temperature increase while CO2 continued to rise isn’t helpful to warmist assertions.

          For more on the problems with the IPCC’s erroneous assertions, see here.

          Or, if you prefer the view of an engineer, this material is also very helpful.

          1. Arrhenius' Ghost


  3. mcraig

    Lindzen and Choi propose a small negative feedback while the IPCC proposes a massive positive feedback.

    There’s no evidence for either. Thus, the loudest wins, not science. The truth is we don’t know.

    1. gallopingcamel

      While I am a fan of Richard Lindzen I am disappointed that he gives credence to the Arrhenius theory by discussing the “Sensitivity Constant”

      If you want to explain Earth’s climate in terms of [CO2], a sensitivity constant won’t help you. What you need is a “Sensitivity Variable” that can be adjusted from -2 to +16 Kelvin per doubling of CO2. Once you can believe that kind of absurdity you will be able to publish papers like this piece of nonsense from James Hansen et al.

      If you examine Figure 7a carefully you will find it assumes -16 K per halving of [CO2] which is what you need to explain the last seven glaciation cycles in terms of CO2. However Hansen can’t explain why temperature led [CO2] by >500 years.

      Please take time to read section (d) “Runaway Greenhouse” in the above paper. It is a wonderful example of gobbledygook paid for by our stupid government.

    2. yonason

      “There’s no evidence for either. ” – mcraig

      Well, at least Lindzen and Choi base there wprl on an analysis of actual data. Spencer seemed to think back in 2009 that they hadn’t yet nailed it down, though.

      Since then L&C have published in 2011, as have Spencer & Brasswell. These are also criticized by both the usual suspects, as well as some I generally trust. Still, when compared with reality, they appear closer than the IPCC, so dismissing both as equally flawed seems to do the not-IPCC efforts, and climate science, a big disservice. …especially since the IPCC guys get so much more wrong than they do.

    3. yonason

      As I say in the comment that hasn’t yet appeared as of this posting, I’m siding with Lindzen & Choi on this one.

  4. DirkH

    Government scientists find out that Global Warming *COULD* cause a giant allergy wave within the next 35 years, increasing the number of Ambrosia allergy community members (“Sufferers” is a discriminatory non-inclusive term) from 33 to 77 million members (I think for the EU that is).
    German article:

    Now we know why the CDU steals 30 billion Euros a year from the Germans to erect wind turbines and solar panels: They want to prevent this terrible allergy from spreading.

    SEE? If one child doesn’t become a member of the allergy community that otherwise would have, isn’t that worth ALL YOUR MONEY?

    That’s the kind of excuse they’re now being reduced too. It’s so barmy. I think all the good phantasists work for NATO these days.

  5. cementafriend

    The IPCC and all the authors of the other mentioned references do not understand basic heat transfer technology which is an engineering subject and has been since about 1800 from the work of Lasare Carnot (father of Sadi Carnot after whom the Carnot cycle is named). Yes, CO2 does absorb some heat by radiation but the amount of heat energy absorbed by CO2 in the atmosphere from earth’s surface (calculated by the equation determined by Prof Hoyt Hottel -late Prof of Chemical Engineering at MIT) is insignificant. The supposed figure of surface heating by CO2 of 3-4W/m2 is pure fiction. The heat absorbed by CO2 in the atmosphere is transferred by mixing with other gases (mainly O2 & N2) or is radiated to space. There is no downward radiation to the surface. measurements and other proxy data (such as icecore information) that temperature leads leads over daily, seasonal, 60 year, 120 year and even 1000 year cycles. The reason is very obvious because the solubility of CO2 in water decreases with increasing temperatures. This can be seen in the higher pH (8.1-8.3) of warm surface waters around tropical islands in the Pacific Ocean compared to the that of up-welling cold water from deep sea and waters in Polar regions (pH 7.5-7.7) As the ocean surface warms as it did in the mid to late 1930’s it results in increased CO2 in the atmosphere as it did in the early 1940’s (a lead of temperature of about 5 years)
    The sensitivity (as defined by the IPCC) due to CO2 should be unmeasurable and close to zero.