Recent CO2 Climate Sensitivity Estimates Continue Trending Towards Zero

Updated: The Shrinking

CO2 Climate Sensitivity

A recently highlighted paper published by atmospheric scientists Scafetta et al., (2017) featured a graph (above) documenting post-2000 trends in the published estimates of the Earth’s climate sensitivity to a doubling of CO2 concentrations (from 280 parts per million to 560 ppm).

The trajectory for the published estimates of transient climate response (TCR, the average temperature response centered around the time of CO2 doubling) and equilibrium climate sensitivity (ECS, the temperature response upon reaching an equilibrium state after doubling) are shown to be declining from an average of about 3°C earlier in the century to below 2°C and edging towards 1°C for the more recent years.

This visual evidence would appear to indicate that past climate model determinations of very high climate sensitivity (4°C, 5°C, 6°C and up) have increasingly been determined to be in error.  The anthropogenic influence on the Earth’s surface temperature has likely been significantly exaggerated.

Scafetta et al., 2017   Since 2000 there has been a systematic tendency to find lower climate sensitivity values. The most recent studies suggest a transient climate response (TCR) of about 1.0 °C, an ECS less than 2.0 °C and an effective climate sensitivity (EfCS) in the neighborhood of 1.0 °C.”

Thus, all evidences suggest that the IPCC GCMs at least increase twofold or even triple the real anthropogenic warming. The GHG theory might even require a deep re-examination.”

An Update On The Gradually Declining Climate Sensitivity

The graph shown in Scafetta et al. (2017) ends in 2014, which means that papers published in the last 3 years are not included.   Also, there were several other published climate sensitivity papers from the last decade that were excluded from the analysis, possibly because they did not include and/or specify TCR and/or ECS estimates in isolation, but instead just used a generic doubled-CO2 climate sensitivity value (shown in purple here).

Below is a new, updated graph that (1) includes some of the previously unidentified papers and (2) adds the 10 – 12 climate sensitivity papers published in the last 3 years.  Notice, again, that the trend found in published papers has continued downwards, gradually heading towards zero.  The reference list for the over 20 additional papers used for the updated analysis is also included below.

For a more comprehensive list of over 60 papers with very low (<1°C) climate sensitivity estimates, see here.

Smirnov, 2017 (~0.4°C)

It is shown that infrared emission of the atmosphere is determined mostly by atmospheric water. One can separate the flux of outgoing infrared radiation of the atmosphere from that towards the Earth. The fluxes due to rotation-vibration transitions of atmospheric   CO2  molecules are evaluated. Doubling of the concentration of  CO2 molecules in the atmosphere that is expected over 130 years leads to an increase of the average Earth temperature by (0.4±0.2) K mostly due to the flux towards the Earth if other atmospheric parameters are not varied.

Smirnov, 2016

[W]e take into account that CO2 molecules give a small contribution to the heat Earth balance and, therefore, one can use the altitude distribution of the temperature for the standard atmosphere model [1], and a variation of the CO2 concentration does not influence this distribution.  …  [I]njection of CO2 molecules into the atmosphere leads to a decrease of the outgoing radiation flux that causes a decrease of the average Earth temperature. But this decrease is below 0.1K that is the accuracy of determination of this value.  Thus, the presence of carbon dioxide in the atmosphere decreases the outgoing atmospheric radiative flux that leads to a decrease of the Earth temperature by approximately (1.8 ± 0.1) K. The change of the average temperature at the double of the concentration of atmospheric CO2 molecules is determined by the transition at 667cm−1 only and is lower than 0.1K.
In particular, doubling of the concentration of CO2 molecules compared to the contemporary content increases the global Earth temperature by ΔT = 0.4 ± 0.2K. … From this we have that the average temperature variation ΔT = 0.8 ◦C from 1880 up to now according to NASA data may be attained by the variation of the water concentration by 200ppm or Δu/u ≈ 0.07, Δu = 0.2. Note that according to formula (2) the variation of an accumulated concentration of CO2 molecules from 1959 (from 316ppm up to 402ppm) leads to the temperature variation ΔT = 0.15°C. One can see that the absorption of a water molecule in infrared spectrum is stronger than that of the CO2 molecule because of their structures, and the injection of water molecules in the atmosphere influences its heat balance more strongly than the injection of CO2 molecules.

Reinhart, 2017 (<0.24°C)

Our results permit to conclude that CO2 is a very weak greenhouse gas and cannot be accepted as the main driver of climate change. … The assumption of a constant temperature and black body radiation definitely violates reality and even the principles of thermodynamics. … [W]e conclude that the temperature increases predicted by the IPCC AR5 lack robust scientific justification. … A doubling [to 800 ppm] of the present level of CO2 [400 ppm] results in  [temperature change] < 0.24 K. … [T]he scientific community must look for causes of climate change that can be solidly based on physics and chemistry. … The observed temperature increase since pre-industrial times is close to an order of magnitude higher than that attributable to CO2.

Abbot and Marohasy, 2017  (0.6°C equilibrium)

The largest deviation between the ANN [artificial neural network] projections and measured temperatures for six geographically distinct regions was approximately 0.2 °C, and from this an Equilibrium Climate Sensitivity (ECS) of approximately 0.6 °C [for a doubling of CO2 from 280 ppm to 560 ppm plus feedbacks] was estimated. This is considerably less than estimates from the General Circulation Models (GCMs) used by the Intergovernmental Panel on Climate Change (IPCC), and similar to estimates from spectroscopic methods.
The proxy measurements suggest New Zealand’s climate has fluctuated within a band of approximately 2°C since at least 900 AD, as shown in Figure 2. The warming of nearly 1°C since 1940 falls within this band. The discrepancy between the orange and blue lines in recent decades as shown in Figure 3, suggests that the anthropogenic contribution to this warming could be in the order of approximately 0.2°C. [80% of the warming since 1940 may be due natural factors].

 Harde, 2016 (0.7°C equilibrium)

Including solar and cloud effects as well as all relevant feedback processes our simulations give an equilibrium climate sensitivity of CS = 0.7 °C (temperature increase at doubled CO2) and a solar sensitivity of SS = 0.17 °C (at 0.1 % increase of the total solar irradiance). Then CO2 contributes 40 % and the Sun 60 % to global warming over the last century.

Bates, 2016  (~1°C)

Estimates of 2xCO2 equilibrium climate sensitivity (EqCS) derive from running global climate models (GCMs) to equilibrium. Estimates of effective climate sensitivity (EfCS) are the corresponding quantities obtained using transient GCM output or observations. The EfCS approach uses an accompanying energy balance model (EBM), the zero-dimensional model (ZDM) being standard. GCM values of EqCS and EfCS vary widely [IPCC range: (1.5, 4.5)°C] and have failed to converge over the past 35 years. Recently, attempts have been made to refine the EfCS approach by using two-zone (tropical/extratropical) EBMs. When applied using satellite radiation data, these give low and tightly-constrained EfCS values, in the neighbourhood of 1°C. … The central conclusion of this study is that to disregard the low values of effective climate sensitivity (≈1°C) given by observations on the grounds that they do not agree with the larger values of equilibrium, or effective, climate sensitivity given by GCMs, while the GCMs themselves do not properly represent the observed value of the tropical radiative response coefficient, is a standpoint that needs to be reconsidered.

Evans, 2016 (<0.5°C equilibrium)

The conventional basic climate model applies “basic physics” to climate, estimating sensitivity to CO2. However, it has two serious architectural errors. It only allows feedbacks in response to surface warming, so it omits the driver-specific feedbacks. It treats extra-absorbed sunlight, which heats the surface and increases outgoing long-wave radiation (OLR), the same as extra CO2, which reduces OLR from carbon dioxide in the upper atmosphere but does not increase the total OLR. The rerouting feedback is proposed. An increasing CO2 concentration warms the upper troposphere, heating the water vapor emissions layer and some cloud tops, which emit more OLR and descend to lower and warmer altitudes. This feedback resolves the nonobservation of the “hotspot.” An alternative model is developed, whose architecture fixes the errors. By summing the (surface) warmings due to climate drivers, rather than their forcings, it allows driver-specific forcings and allows a separate CO2 response (the conventional model applies the same response, the solar response, to all forcings). It also applies a radiation balance, estimating OLR from properties of the emission layers. Fitting the climate data to the alternative model, we find that the equilibrium climate sensitivity is most likely less than 0.5°C, increasing CO2 most likely caused less than 20% of the global warming from the 1970s, and the CO2 response is less than one-third as strong as the solar response. The conventional model overestimates the potency of CO2 because it applies the strong solar response instead of the weak CO2response to the CO2 forcing.

Gervais, 2016 [full]  (<0.6°C transient)

Conclusion: Dangerous anthropogenic warming is questioned (i) upon recognition of the large amplitude of the natural 60–year cyclic component and (ii) upon revision downwards of the transient climate response consistent with latest tendencies shown in Fig. 1, here found to be at most 0.6 °C once the natural component has been removed, consistent with latest infrared studies (Harde, 2014). Anthropogenic warming well below the potentially dangerous range were reported in older and recent studies (Idso, 1998; Miskolczi, 2007; Paltridge et al., 2009; Gerlich and Tscheuschner, 2009; Lindzen and Choi, 2009, 2011; Spencer and Braswell, 2010; Clark, 2010; Kramm and Dlugi, 2011; Lewis and Curry, 2014; Skeie et al., 2014; Lewis, 2015; Volokin and ReLlez, 2015). On inspection of a risk of anthropogenic warming thus toned down, a change of paradigm which highlights a benefit for mankind related to the increase of plant feeding and crops yields by enhanced CO2 photosynthesis is suggested.

Marvel et al., 2016 (1.8°C transient, 3.0°C equilibrium)

Assuming that all forcings have the same transient efficacy as greenhouse gases, and following a previous study, the best estimate (median) for TCR is 1.3°C. However, scaling each forcing by our estimates of transient efficacy (determined from either iRF or ERF), we obtain a best estimate for TCR of 1.8°C. This scaling simultaneously considers both forcing and ocean heat uptake efficacy. Other estimates of TCR which differ slightly due to choices of base period and uncertainty estimates and the aerosol forcing used, are similarly revised upward when using calculated efficacies.  We apply the same reasoning to estimates of ECS. Using an estimate4 of the rate of recent heat uptake Q = 0.65 ± 0.27 W m-2, we find, assuming all equilibrium efficacies are unity, a best estimate of ECS = 2.0°C, comparable to the previous result of 1.9°C.  However, as with TCR, accounting for differences in equilibrium forcing efficacy revises the estimate upward; our new best estimate (using efficacies derived from the iRF) is 2.9°C. If efficacies are instead calculated from the ERF, the best estimate of ECS is 3.0°C. As for TCR, alternate estimates of ECS are revised upward when efficacies are taken into account.

Soon, Connolly, and Connolly, 2015 [full] (0.44°C)

Nonetheless, let us ignore the negative relationship with greenhouse gas (GHG) radiative forcing, and assume the carbon dioxide (CO2) relationship is valid. If atmospheric carbon dioxide concentrations have risen by ~110 ppmv since 1881 (i.e., 290→400 ppmv), this would imply that carbon dioxide (CO2) is responsible for a warming of at most 0.0011 × 110 = 0.12°C over the 1881-2014 period, where 0.0011 is the slope of the line in Figure 29(a). We can use this relationship to calculate the so-called “climate sensitivity” to carbon dioxide, i.e., the temperature response to a doubling of atmospheric carbon dioxide. According to this model, if atmospheric carbon dioxide concentrations were to increase by ~400 ppmv, this would contribute to at most 0.0011 × 400 = 0.44°C warming. That is, the climate sensitivity to atmospheric carbon dioxide is at most 0.44°C.

Lewis and Curry, 2015 (1.33°C  transient, 1.64°C  equilibrium)

Energy budget estimates of equilibrium climate sensitivity (ECS) and transient climate response (TCR) are derived using the comprehensive 1750–2011 time series and the uncertainty ranges for forcing components provided in the Intergovernmental Panel on Climate Change Fifth Assessment Working Group I Report, along with its estimates of heat accumulation in the climate system. The resulting estimates are less dependent on global climate models and allow more realistically for forcing uncertainties than similar estimates based on forcings diagnosed from simulations by such models. Base and final periods are selected that have well matched volcanic activity and influence from internal variability. Using 1859–1882 for the base period and 1995–2011 for the final period, thus avoiding major volcanic activity, median estimates are derived for ECS of 1.64 K and for TCR of 1.33 K.

Johansson et al., 2015 (2.5°C  equilibrium)

A key uncertainty in projecting future climate change is the magnitude of equilibrium climate sensitivity (ECS), that is, the eventual increase in global annual average surface temperature in response to a doubling of atmospheric CO2 concentration. The lower bound of the likely range for ECS given in the IPCC Fifth Assessment Report was revised downwards to 1.5 °C, from 2 °C in its previous report, mainly as an effect of considering observations over the warming hiatus—the period of slowdown of global average temperature increase since the early 2000s. Here we analyse how estimates of ECS change as observations accumulate over time and estimate the contribution of potential causes to the hiatus. We find that including observations over the hiatus reduces the most likely value for ECS from 2.8 °C to 2.5 °C, but that the lower bound of the 90% range remains stable around 2 °C. We also find that the hiatus is primarily attributable to El Niño/Southern Oscillation-related variability and reduced solar forcing.

Kissin, 2015 (~0.6°C)

[A] doubling the CO2 concentration in the Earth’s atmosphere would lead to an increase of the surface temperature by about +0.5 to 0.7 °C, hardly an effect calling for immediate drastic changes in the planet’s energy policies. An increase in the absolute air humidity caused by doubling the CO2 concentration and the resulting decrease of the outgoing IR flux would produce a relatively small additional effect due to a strong overlap of IR spectral bands of CO2 and H2O, the two compounds primarily responsible for the greenhouse properties of the atmosphere.

Kimoto, 2015  [full] (~0.16°C)

The central dogma is critically evaluated in the anthropogenic global warming (AGW) theory of the IPCC, claiming the Planck response is 1.2K when CO2 is doubled. The first basis of it is one dimensional model studies with the fixed lapse rate assumption of 6.5K/km. It is failed from the lack of the parameter sensitivity analysis of the lapse rate for CO2 doubling. The second basis is the Planck response calculation by Cess in 1976 having a mathematical error. Therefore, the AGW theory is collapsed along with the canonical climate sensitivity of 3K utilizing the radiative forcing of 3.7W/m2 for CO2 doubling. The surface climate sensitivity is 0.14 – 0.17 K in this study with the surface radiative forcing of 1.1 W/m2.

Ollila, 2014 (~0.6°C equilibrium)

According to this study the commonly applied radiative forcing (RF) value of 3.7 Wm-2 for CO2 concentration of 560 ppm includes water feedback. The same value without water feedback is 2.16 Wm-2 which is 41.6 % smaller. Spectral analyses show that the contribution of CO2 in the greenhouse (GH) phenomenon is about 11 % and water’s strength in the present climate in comparison to CO2 is 15.2. The author has analyzed the value of the climate sensitivity (CS) and the climate sensitivity parameter (l) using three different calculation bases. These methods include energy balance calculations, infrared radiation absorption in the atmosphere, and the changes in outgoing longwave radiation at the top of the atmosphere. According to the analyzed results, the equilibrium CS (ECS) is at maximum 0.6 °C and the best estimate of l is 0.268 K/(Wm-2 ) without any feedback mechanisms.

Loehle, 2014  (1.1°C  transient, 2.0°C  equilibrium)

Estimated sensitivity is 1.093 °C (transient) and 1.99 °C (equilibrium).  Empirical study sensitivity estimates fall below those based on GCMs.

Skeie et al., 2014  (1.8°C  equilibrium)

Equilibrium climate sensitivity (ECS) is constrained based on observed near-surface temperature change, changes in ocean heat content (OHC) and detailed radiative forcing (RF) time series from pre-industrial times to 2010 for all main anthropogenic and natural forcing mechanism. The RF time series are linked to the observations of OHC and temperature change through an energy balance model (EBM) and a stochastic model, using a Bayesian approach to estimate the ECS and other unknown parameters from the data. For the net anthropogenic RF the posterior mean in 2010 is 2.0 Wm−2, with a 90% credible interval (C.I.) of 1.3 to 2.8 Wm−2, excluding present-day total aerosol effects (direct + indirect) stronger than −1.7 Wm−2. The posterior mean of the ECS is 1.8 °C, with 90% C.I. ranging from 0.9 to 3.2 °C, which is tighter than most previously published estimates.

Scafetta, 2013 (1.5°C)

A quasi 60-year natural oscillation simultaneously explains the 1850–1880, 1910–1940 and 1970–2000 warming periods, the 1880–1910 and 1940–1970 cooling periods and the post 2000 GST plateau. This hypothesis implies that about 50% of the ~ 0.5 °C global surface warming observed from 1970 to 2000 was due to natural oscillations of the climate system, not to anthropogenic forcing as modeled by the CMIP3 and CMIP5 GCMs. Consequently, the climate sensitivity to CO2 doubling should be reduced by half, for example from the 2.0–4.5 °C range (as claimed by the IPCC, 2007) to 1.0–2.3 °C with a likely median of ~ 1.5 °C instead of ~ 3.0 °C.

Asten, 2012 (1.1°C)

Climate sensitivity estimated from the latter is 1.1 ± 0.4 °C (66% confidence) compared with the IPCC central value of 3 °C. The post Eocene-Oligocene transition (33.4 Ma) value of 1.1 °C obtained here is lower than those published from Holocene and Pleistocene glaciation-related temperature data (800 Kya to present) but is of similar order to sensitivity estimates published from satellite observations of tropospheric and sea-surface temperature variations. The value of 1.1 °C is grossly different from estimates up to 9 °C published from paleo-temperature studies of Pliocene (3 to 4 Mya) age sediments. 

Lindzen and Choi, 2011 (0.7°C)

As a result, the climate sensitivity for a doubling of CO2 is estimated to be 0.7K (with the confidence interval 0.5K – 1.3K at 99% levels). This observational result shows that model sensitivities indicated by the IPCC AR4 are likely greater than the possibilities estimated from the observations.

Florides and Christodoulides, 2009 (~0.02°C)

A very recent development on the greenhouse phenomenon is a validated adiabatic model, based on laws of physics, forecasting a maximum temperature-increase of 0.01–0.03 °C for a value doubling the present concentration of atmospheric CO2

Gray, 2009 (~0.4°C)

CO2 increases without positive water vapor feedback could only have been responsible for about  0.1 – 0.2 °C of the 0.6-0.7°C global mean surface temperature warming that has been observed since the early 20th  century.  Assuming a doubling of CO2 by the late 21st  century (assuming no  positive water vapor feedback), we should likely expect to see no more than about 0.3-0.5°C global surface warming and certainly not the 2-5°C warming that has been projected by the GCMs [global circulation models].

Chylek et al., 2007 (~0.39°C)

Consequently, both increasing atmospheric concentration of greenhouse gases and decreasing loading of atmospheric aerosols are major contributors to the top-of atmosphere radiative forcing. We find that the climate sensitivity is reduced by at least a factor of 2 when direct and indirect effects of decreasing aerosols are included, compared to the case where the radiative forcing is ascribed only to increases in atmospheric concentrations of carbon dioxide. We find the empirical climate sensitivity to be between 0.29 and 0.48 K/Wm-2 when aerosol direct and indirect radiative forcing is included.

57 responses to “Recent CO2 Climate Sensitivity Estimates Continue Trending Towards Zero”

  1. Pethefin

    Thanks Kenneth for yet another excellent post! It will be interesting to see how the IPCC will manage such development.

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  3. Bitter&twisted


    Post your fantasy comments, please.
    We could all do with a laugh.

    1. SebastianH

      Fantasy is what most papers in that list are writing about. You skeptics should be more skeptic when something seems to support your views than when it opposes your views. Especially when an author uses inappropriate language and celebrates himself/herself for having found something that shows the GHE would be violating one or more laws of physics 😉

      But thanks for the comprehensive list of papers that will surely not be considered by any climate science panel. Not because their “results” would be inconvenient, but because those “results” are largely imagined … fantasy if you want.

      1. Ron

        You certainly gave me my chuckle for the day.

        Such a wordy, finger pointing, character flaw focused attempt at falsifying supported science. Yet… You have absolutely nothing relevant to support your claims of what makes this fantasy. Just a blatant character attack and nothing more. HAHAHAHAHAHAHAHAHAHAHAHA!!!!!!!!!!!!!!!!

        Thank you!!!!!!!!!! This will get me through years to come.

        1. SebastianH

          Do you think (most of) those papers are relevant? Why? Because they suit your narrative? Why aren’t you skeptical about the methods they used to derive at their conclusions?

  4. Bruce of Newcastle

    Back in 2010 I found a value of about 0.7 C/doubling using HadCET and the data from the Armagh weather observatory. That is probably an upper limit since it still assumes greenhouse gases were driving the residual warming after deduction of the effect of the ocean cycles and the indirect effect of the Sun. (The methodology is given and can be replicated with a bit of effort using a spreadsheet.)

    It’s interesting that more and more studies are converging to the same general result: an ECS below 1 C/doubling.

    It is important to underline what that means.

    At 1 C/doubling, another 2 C more warming would require us to burn 10 times the amount of coal, oil and gas than we have done since the start of civilization. But that can’t happen since there isn’t that much coal, oil and gas in existence.

    So any ECS value below 1 C/doubling means global warming is completely harmless.

  5. ClimateOtter

    Yes seb- please explain to us how computer-modeled CS based upon built-in assumptions is superior to observation-based analyses.

  6. Mindert Eiting

    Worth noting perhaps that this development is an example of the well known decline effect in medical and social research. The estimates always trend to zero because the effect is zero. Usually, it begins with fantastic claims based on a false positive in a small sample, subtle errors in experimental design, or biased data.

    1. Pethefin

      Good point! This applies to a number of phenoma in the current post-truth hype-everything-society. I can wait for this anti-enlightment era to end.

      1. SebastianH

        I wonder what happens when you find out that you guys were wrong in a few decades. Can we look back and see what skeptics “predicted” 10 years ago and what really happened?

        1. Mary Brown

          “Climate science” is definitely science. Just because there are many poor practitioners doesn’t mean it’s not science.

        2. Mary Brown

          Scafetta has published his forecasts quite clearly. I think he has the best model I’ve seen. It combines the natural harmonics with climate models reliant on GHG forcings. He adjusts the climate models for their historical bias in the same way MOS adjust weather models for their biases and uncertainties.

          Forecasts and hindcast here…

          So far, the el nino spike has him underperforming the climate models. Time will tell.

  7. Bitter&twisted

    Social “science”, like climate “science” is not social, or science.

    1. Michael Jones

      Ditto for Social Justice!

  8. richard verney

    Don’t forget that back in 1971, NASA/GISS assessed Climate Sensitivity to be around 0.5degC per doubling, and about 0.6degC with water feedback. So it has been known for a very long time that Climate Sensitivity is low.

    We are constantly being told that AGW is grounded upon basic physics going back more than 100 years. We have known the infra red absorbing characteristics of CO2 for generations. There is no new physics or properties of CO2 that have come to light after the NASA/GISS 1971 paper such that there is no reason to consider that paper to be fundamentally flawed, or superseded by a better understanding of known physics.

    The difference is one of politics. In 1971, Climate Scientists were pushing global cooling. Hence, they wanted to show that CO2 whilst causing warming, was not as important as high aerosol emissions that were causing cooling. Thus they portrayed low sensitivity to CO2, and high sensitivity to aerosols.

    Now the meme has changed. Political activists now wish to promote global warming so they have had to switch around the sensitivities, and the warmist now want people to believe that there is high sensitivity to CO2, and lower sensitivity to aerosol emissions.

    The fluidity of the science tells you everything you need to know. Science that can shift in this manner is not science, but rather simply politically driven to promote an agenda of someone’s utopian dream (socialism new world order).

    See the Schneider 1971 paper (which incidentally utilized a model produced by no other than James Hansen). Science Volume 173 (July 19710 pages 138 to 141.

  9. Rodney W. Nichols

    This summary is extremely useful. Thanks. In debating the climate in DC and rest of USA, almost no one thinks about any estimate except the dreaded >2.C

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  11. betapug

    The fear inducing power of “global warming” seems to be declining! Truly “it is worse than we thought”.

  12. dai davies

    All IPCC and contemporary climate analysis is based on the assumption that radiative (aka greenhouse) gasses ‘trap’ infrared radiation. This is wrong, they merely delay heat transfer to space.

    A second false assumption is that the radiative delay (aka greenhouse) effect is the only mechanism that can account for Earth’s surface temperature. Thermal buffering by the atmosphere of the day/night temperature cycle can account for our surface temperature.

    The total current contribution of CO2 to surface temperature is approximately 0.01 C.



  13. Atomsk's Sanakan

    If there are really “no tricks” here, then why are you tricking people? For example, your first listed source “Reinhert, 2017” is not a peer-reviewed study; it’s a blogpost from “Toutes les énergies”, as potholer54 pointed out. It calls itself a blog: “Ce blog est un espace de liberté, pour des auteurs francophones.” The dangers of relying such blogs are well-known:

    “Unlike mainstream climate scientists, who publish primarily in peer reviewed journals, these critics typically employ a range of non-peer-reviewed outlets, ranging from blogs to the books we are examining. […]
    The general lack of peer review allows authors or editors of denial books to make inaccurate assertions that misrepresent the current state of climate science. Like the vast range of other non-peer-reviewed material produced by the denial community, book authors can make whatever claims they wish, no matter how scientifically unfounded.”

    And how about the fact that many of these so-called “studies” are published in predatory, open-access, online “journals” with no impact factor and which are not listed in reputable citation indexes (like the Master Journals list)? Thus the studies are unlikely to have undergone competent peer review.

    For example, the “Abbot and Marohasy, 2017” “study” was incredily bad. They don’t even access the data sources they’re supposed to be using, and instead digitize images from papers they saw. This leads them to screw up their figure 12, which is a pretty poor modification of Moberg 2005:

    “Climate: past ranges and future changes”
    “Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data”

    Their figure 12 excludes much of the recent global warming, along with southern hemisphere trends. Zeke Hausfather and Gavin Schmidt dumb this down rather nicely here:

    Including the southern hemisphere and recent global warming results in the standard hockey stick pattern than would have likely increases Abbot and Marohasy’s climate sensitivity estimate. For example:

    Figure 2:
    “Pacific Ocean Heat Content During the Past 10,000 Years”

    So no wonder Abbot and Marohasy decided to exclude that data; it would have gotten in the way of their goal of showing low climate sensitivity. Competent peer review would have prevented Abbot and Marohasy’s attempt at excluding data. But competent peer review apparently was not applied to Abbot and Marohasy’s “study”. Unsurprisingly, the predatory “journal” “Abbot and Marohasy, 2017” was published in will be closing down in a few months:

    Anyway, your figure commits at least three additional errors [citations in brackets]:

    A1) It is less comprehensive than a scientific review of the literature; this review presents recent evidence in support of a higher climate sensitivity [1].
    A2) It excludes other studies that show higher climate sensitivity [2 – 17].
    A3) It excludes papers that show flaws in some of the studies listed in your figure [5; 6; 8 – 12; 18, page 1375].

    Reasons A2 and A3 are connected since correcting the flaws in the studies listed in your figure, tends to increase the studies’ climate sensitivity estimates [5; 6; 8 – 12; 18].

    Citation list:

    1. “Beyond equilibrium climate sensitivity”
    2. “Climate sensitivity in the geologic past”
    3. “Deep time evidence for climate sensitivity increase with warming”
    4. “Observational constraints on mixed-phase clouds imply higher climate sensitivity”
    5. “Reconciled climate response estimates from climate models and the energy budget of Earth”
    6. “Implications for climate sensitivity from the response to individual forcings”
    7. “Implications of potentially lower climate sensitivity on climate projections and policy”
    8. “Disentangling greenhouse warming and aerosol cooling to reveal Earth’s climate sensitivity”
    9. “Inhomogeneous forcing and transient climate sensitivity”
    10. “On a minimal model for estimating climate sensitivity”
    11. “Corrigendum to “On a minimal model for estimating climate sensitivity” [Ecol. Model. 297 (2015), 20-25]”
    12. “Projection and prediction: Climate sensitivity on the rise”
    13. “Spread in model climate sensitivity traced to atmospheric convective mixing”
    14. “Long-term cloud change imprinted in seasonal cloud variation: More evidence of high climate sensitivity”
    15. “Nonlinear climate sensitivity and its implications for future greenhouse warming”
    16. “Natural variability, radiative forcing and climate response in the recent hiatus reconciled”
    17. “A less cloudy future: the role of subtropical subsidence in climate sensitivity”
    18. “Misdiagnosis of Earth climate sensitivity based on energy balance model results”

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  15. Svend Ferdinandsen

    If you extend the graphs the sensitivity might be negative around 2100.
    They are falling steadily without any levelling out, so it could be interesting times ahead.
    IPCC has in due time changed from GW to Climate Change, so the scare can be uphold. No one remember at that time, that Climate Change was caused by temperature and not CO2 in itself.

    1. yonason

      “If you extend the graphs the sensitivity might be negative around 2100.” – Svend Ferdinandsen

      So, some time after 2100 CO2 is going to stop warming the world, and start cooling it?

      That’s going to leave a mark. No wonder they are in such a hurry to get all their phony mitigation schemes through and fascist restrictive laws past before their scam is discovered.

  16. dan

    Potholer54 gives an explanation of why this article is based on junk science:

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  19. Statt Klimakonferenz – Schnorchelkurs für Barbara Hendricks – EIKE – Europäisches Institut für Klima & Energie

    […] Wie erwähnt, liegen die Schätzungen der Klimasensitivität seit beinahe 30 Jahren im Bereich zwischen 1,5 und 4,5 Grad. Der „Erfinder“ der Treibhausthese, Svante Arrhenius, schätzte sie Anfang des 20. Jahrhunderts auf 5 bis 6 Grad Celsius, war also gar nicht so weit vom heutigen oberen Schätzwert entfernt. Die tatsächliche Temperatur-Entwicklung deutet jedoch auf einen Wert hin, der am unteren Ende der Skala, also bei undramatischen 1 bis 1,5 Grad liegt. Die Schätzungen werden mit jeder neuen Studie immer geringer. […]