From Science Matters

By Ron Clutz

In  2019, the iconic email from the Climategate leak included a comment by Phil Jones about the “trick” used by Michael Mann to “hide the decline,” in his Hockey Stick graph, referring to tree proxy temperatures  cooling rather than warming in modern times.  Now we have an important paper demonstrating that climate models insist on man-made global warming only by hiding the incline of natural warming in Pre-Industrial times.  The paper is From Behavioral Climate Models and Millennial Data to AGW Reassessment by Philippe de Larminat.  H/T No Tricks Zone. Excerpts in italics with my bolds.

Abstract

Context. The so called AGW (Anthropogenic Global Warming), is based on thousands of climate simulations indicating that human activity is virtually solely responsible for the recent global warming. The climate models used are derived from the meteorological models used for short-term predictions. They are based on the fundamental and empirical physical laws that govern the myriad of atmospheric and oceanic cells integrated by the finite element technique. Numerical approximations, empiricism and the inherent chaos in fluid circulations make these models questionable for validating the anthropogenic principle, given the accuracy required (better than one per thousand) in determining the Earth energy balance.

Aims and methods. The purpose is to quantify and simulate behavioral models of weak complexity, without referring to predefined parameters of the underlying physical laws, but relying exclusively on generally accepted historical and paleoclimate series.

Results. These models perform global temperature simulations that are consistent with those from the more complex physical models. However, the repartition of contributions in the present warming depends strongly on the retained temperature reconstructions, in particular the magnitudes of the Medieval Warm Period and the Little Ice Age. It also depends on the level of the solar activity series. It results from these observations and climate reconstructions that the anthropogenic principle only holds for climate profiles assuming almost no PCA neither significant variations in solar activity. Otherwise, it reduces to a weak principle where global warming is not only the result of human activity, but is largely due to solar activity.

Discussion

GCMs (short acronym for AOCGM: Atmosphere Ocean General Circulation Models, or for Global Climate model) are fed by series related to climate drivers. Some are of human origin: fossil fuel combustion, industrial aerosols, changes in land use, condensation trails, etc. Others are of natural origin: solar and volcanic activities, Earth’s orbital parameters, geomagnetism, internal variability generated by atmospheric and oceanic chaos. These drivers, or forcing factors, are expressed in their own units: total solar irradiance (W m–2), atmospheric concentrations of GHG (ppm), optical depth of industrial or volcanic aerosols (dimless), oceanic indexes (ENSO, AMO…), or by annual growth rates (%). Climate scientists have introduced a metric in order to characterize the relative impact of the different climate drivers on climate change. This metric is that of radiative forcings (RF), designed to quantify climate drivers through their effects on the terrestrial radiation budget at the top of the atmosphere (TOA).

However, independently of the physical units and associated energy properties of the RFs, one can recognize their signatures in the output and deduce their contributions. For example, volcanic eruptions are identifiable events whose contributions can be quantified without reference to either their assumed radiative forcings, or to physical modeling of aerosol diffusion in the atmosphere. Similarly, the Preindustrial Climate Anomalies (PCA) gathering the Medieval Warm Period (MWP) and the Little Ice Age (LIA), shows a profile similar to that of the solar forcing reconstructions. Per the methodology proposed in this paper, the respective contributions of the RF inputs are quantified through behavior models, or black-box models.

Now, Figures 1-a and 1-b presents simulations obtained from the models identified under two different sets of assumptions, detailed in sections 6 and 7 respectively.

In both cases, the overall result for the global temperature simulation (red) fits fairly well with the observations (black).  Curves also show the forcing contributions to modern warming (since 1850). From this perspective, the natural (green) and anthropogenic (blue) contributions are in strong contradiction between panels (a) and (b). This incompatibility is at the heart of our work.

Simulations in panel (a) are calculated per section 6, where the scaling multipliers planned in the model are locked to unity, so that the radiative forcing inputs are constrained to strictly comply with the IPCC quantification. The remaining parameters of the black-box model are adjusted in order to minimize the deviation between the observations (black curve) and the simulated outputs (red). Per these assumptions, the resulting contributions (blue vs. green) comply with the AGW principle. Also, the conformity of the results with those of the CMIP supports the validity of the type of behavioral model adopted for our simulations.

Paleoclimate Temperatures

Although historically documented the Medieval Warm Period (MWP) and the Little Ice Age (LIA) don’t make consensus about their amplitudes and geographic extensions [2, 3]. In Fig. 7.1-c of the First Assessment Report of IPCC, a reconstruction from showed a peak PCA amplitude of about 1.2 °C [4]. Then later on, a reconstruction by the so-called ‘hockey stick graph’, was reproduced five times in the IPCC Third Assessment Report (2001), wherein there was no longer any significant MWP [5].

After, 2003 controversies reference to this reconstruction had disappeared from subsequent IPCC reports:it is not included among the fifteen paleoclimate reconstructions covering the millennium period listed in the fifth report (AR5, 2013) [6]. Nevertheless, AR6 (2021) revived a hockey stick graph reconstruction from a consortium initiated by a network “PAst climate chanGES” [7,8]. The IPCC assures (AR6, 2.3.1.1.2): “this synthesis is generally in agreement with the AR5 assessment”.

Figure 2 below puts this claim into perspective. It shows the fifteen reconstructions covering the preindustrial period accredited by the IPCC in AR5 (2013, Fig. 5.7 to 5.9, and table 5.A.6), compiled (Pangaea database) by [7]. Visibly, the claimed agreement of the PAGES2k reconstruction (blue) with
the AR5 green lines does not hold.

Conclusion

In section 8 above, a set of consistent climate series is explored, from which solar activity appears to be the main driver of climate change. To eradicate this hypothesis, the anthropogenic principle requires four simultaneous assessments:

♦  A strong anthropogenic forcing, able to account for all of the current warming.
♦  A low solar forcing.
♦  A low internal variability.
♦  The nonexistence of significant pre-industrial climate anomalies, which could indeed be explained by strong solar forcing or high internal variability.

None of these conditions is strongly established, neither by theoretical knowledge nor by historical and paleoclimatic observations. On the contrary, our analysis challenges them through a weak complexity model, fed by accepted forcing profiles, which are recalibrated owning to climate observations. The simulations show that solar activity contributes to current climate warming in proportions depending on the assessed pre-industrial climate anomalies.

Therefore, adherence to the anthropogenic principle requires that when reconstructing climate data, the Medieval Warming Period and the Little Ice Age be reduced to nothing, and that any series of strongly varying solar forcing be discarded. 

Background on Disappearing Paleo Global Warming

Rise and Fall of the Modern Warming Spike