IPCC Model Scenarios Compared To Actual Measured Temperatures

 by Bob Irvine.

The IPCC and others have been making global temperature projections for some time now for various emission scenarios. These projections have invariably failed but the obvious corollary of this, that the modelled climate sensitivity is too high, has never been addressed.

In an effort to hold the IPCC accountable, I have compared actual measured temperatures with two of their scenarios from the AR4 report in 2007. The B1 and A2 scenarios. See Appendix “A” for the relevant section of the AR4 report.

The A2 scenario (The grey line in Fig 1) in this report matches well with RCP8.5 and is the closest match we have to actual emissions for the period 2005 to 2020 (See Fig 2). The A2 scenario, as described below, estimates a central temperature increase by the end of this century of about 3.4C above the 1980-1999 average, while RCP8.5 approximates this with temperature at the end of the century expected to be 4.5C above preindustrial.

The other (The yellow line in Fig. 1) is what I would call the Green New Deal dream line. The B1 scenario is used and is described in the IPCC report as a world “with reductions in material intensity and the introduction of clean and resource-efficient technologies.”

The measured temperature is below both these scenarios and indicates that the IPCCs high sensitivities are not supported by the evidence. It is even lower than the Green New Deal’s wildest expectations (B1) and as such should have been met with relief and admissions that they got it wrong. Instead, we see more fake hockey sticks and misleading statements to the effect that “it is worse than we thought”.

(Grey) The temperature that should be consistent with our current emissions if the IPCCs climate sensitivities are accurate. According to the A2 scenario and RCP8.5.

(Yellow) The temperature that should be consistent with our best-case reduction in fossil fuel use, again assuming the IPCC sensitivities are correct. According to the B1 scenario.

(Blue and Orange) The measured temperature from UAH and NASA GISS respectively.

RCP8.5, THE MOST ACCURATE PATHWAY

RCP8.5 (And presumably A2) has been attacked lately as being extreme, alarmist and misleading. (Hausfather and Peters 2020, Burgess et al 2020.). These statements themselves actually mislead.

According to this Schwalm et al 2020 Report in PNAS, RCP8.5 is the pathway that most closely matches actual emissions to 2020 and likely emissions to 2050 and is useful out to the end of this century.

RCP8.5 tracks cumulative CO2 emissions | PNAS 

From this Report;

“  …among the RCP scenarios, RCP8.5 agrees most closely—within 1% for 2005 to 2020 (Fig 2)—with total cumulative CO₂ emissions (Friedlingstein et al 2019)). The next-closest scenario, RCP2.6, underestimates cumulative emissions by 7.4%.”

As is clear in the PNAS graph below, the RCP8.5 pathway best describes current emissions and, also, best describes emissions under a “business as usual” scenario to 2050.

For this reason, it is legitimate to compare RCP8.5 projections with current temperatures. The conclusion from Fig 1. must be that the climate sensitivities used to produce these temperature projections are, likely, too high by a significant amount.

Fig. 2.

Total cumulative CO₂ emissions since 2005 through 2020, 2030, and 2050. Data sources: Historical data from Global Carbon Project (Friedlingstein et al 2019); emissions consistent with RCPs are from RCP Database Version 2.0.5 (https://tntcat.iiasa.ac.at/RcpDb/); “business as usual” and “business as intended” are from IEA Current Policies and Stated Policies scenarios, respectively (IEA, 2019). IEA data (fossil fuel from energy use only) was combined with future land use and industrial emissions to estimate total CO₂ emissions. Future land use emissions estimated from linear trend fit to 2005 to 2019 Global Carbon Project land use emissions data (Friedlingstein et al, 2019). Industrial emissions estimated as 10% of total emissions. Final IEA data use historical values through 2020 and scenario values thereafter. Biotic feedbacks are not included in any IEA-based estimate. Note that RCP forcing levels are intended to represent the sum of biotic feedbacks and human emissions.

CURRENT EMISSIONS ARE FOLLOWING THE HIGHER PATHWAYS

Intermittent renewables still supply a relatively insignificant proportion of global energy consumption. (See Fig 3). The enormous cost involved in producing this intermittent energy has made little discernible difference to CO2 concentrations. (See Fig 4).

CO2 concentrations continue to rise exponentially and are consistent with the RCP8.5 pathway. (See Fig 2).

Global temperatures are not rising as expected. (See Fig 1). The most likely reason for this is that the climate sensitivities used by the IPCC are much too high.

APPENDIX “A”

Below is an extract from the AR4 report that generated the A2 and B1 scenarios used here.

Rut temp

A report of Working Group I of the

Intergovernmental Panel on Climate Change

Summary for Policymakers

Drafting Authors:

Richard B. Alley, Terje Berntsen, Nathaniel L. Bindoff, Zhenlin Chen, Amnat Chidthaisong, Pierre Friedlingstein,

Jonathan M. Gregory, Gabriele C. Hegerl, Martin Heimann, Bruce Hewitson, Brian J. Hoskins, Fortunat Joos, Jean Jouzel, Vladimir Kattsov, Ulrike Lohmann, Martin Manning, Taroh Matsuno, Mario Molina, Neville Nicholls, Jonathan Overpeck,

Dahe Qin, Graciela Raga, Venkatachalam Ramaswamy, Jiawen Ren, Matilde Rusticucci, Susan Solomon, Richard Somerville, Thomas F. Stocker, Peter A. Stott, Ronald J. Stouffer, Penny Whetton, Richard A. Wood, David Wratt

Draft Contributing Authors:

J. Arblaster, G. Brasseur, J.H. Christensen, K.L. Denman, D.W. Fahey, P. Forster, E. Jansen, P.D. Jones, R. Knutti,

H. Le Treut, P. Lemke, G. Meehl, P. Mote, D.A. Randall, D.A. Stone, K.E. Trenberth, J. Willebrand, F. Zwiers

This Summary for Policymakers should be cited as:

IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working

Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning,

Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Table SPM.3. Projected global average surface warming and sea level rise at the end of the 21st century. {10.5, 10.6, Table 10.7}

Table notes:

^a These estimates are assessed from a hierarchy of models that encompass a simple climate model, several Earth System Models of Intermediate Complexity and a large number of Atmosphere-Ocean General Circulation Models (AOGCMs).

^b Year 2000 constant composition is derived from AOGCMs only.

Summary for Policymakers

Figure SPM.5. Solid lines are multi-model global averages of surface warming (relative to 1980–1999) for the scenarios A2, A1B and B1, shown as continuations of the 20th century simulations. Shading denotes the ±1 standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at year 2000 values. The grey bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. The assessment of the best estimate and likely ranges in the grey bars includes the AOGCMs in the left part of the figure, as well as results from a hierarchy of independent models and observational constraints. {Figures 10.4 and 10.29}

Summary for Policymakers

THE EMISSION SCENARIOS OF THE IPCC SPECIAL REPORT ON EMISSION SCENARIOS (SRES)17

A1. The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 scenario family develops into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis: fossil-intensive (A1FI), non-fossil energy sources (A1T) or a balance across all sources (A1B) (where balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end use technologies).

A2. The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is self- reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing population. Economic development is primarily regionally oriented and per capita economic growth and technological change more fragmented and slower than other storylines.

B1. The B1 storyline and scenario family describes a convergent world with the same global population, that peaks in mid-century and declines thereafter, as in the A1 storyline, but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.

B2. The B2 storyline and scenario family describes a world in which the emphasis is on local solutions to economic, social and environmental sustainability. It is a world with continuously increasing global population, at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented towards environmental protection and social equity, it focuses on local and regional levels.

An illustrative scenario was chosen for each of the six scenario groups A1B, A1FI, A1T, A2, B1 and B2. All should be considered equally sound.

The SRES scenarios do not include additional climate initiatives, which means that no scenarios are included that explicitly assume implementation of the United Nations Framework Convention on Climate Change or the emissions targets of the Kyoto Protocol.

¹⁷ Emission scenarios are not assessed in this Working Group I Report of the IPCC. This box summarising the SRES scenarios is taken from the TAR and has been subject to prior line-by-line approval by the Panel.