New IPCC economic models

An article from Forbes Magazine on the IPCC’s latest “socio-economic modelling” of emission and growth scenarios has attracted a lot of attention because it claims the IPCC now shows that…

The highest economic growth model leads to the lowest level of emissions considered. Less economic growth leads to higher emissions. Extract from Forbes

But the authors of the IPCC paper disclaim any such projection. The emission-trajectories are a given (exogenous) in their new “socio-economic” models, not the outcomes of the modelling.

The IPCC authors have taken four emission-scenarios (with different radiative-forcing outcomes according to the IPCCs dogma of the origins of radiative forcing) and constructed around each of them some socio-economic “scenarios” in the form of income, land-use, energy-mix and population trajectories over the rest of this century that, they say, are individually consistent with the given emission trajectories.

The IPCC paper notes that the four socio-economic scenarios have been differently constructed, containing different mixes of energy use, land use and technology. They are therefore incommensurable; they do not comprise different sets of policy recommendations(!) and cannot be allocated any order of preference(!).

In truth, the confusing language used in the report—steeped in the IPCC’s liturgy—and many detailed caveats in the fine print make it nearly impossible to know what the results mean. To illustrate; the following is an extract of the fine print from section 4.1 of the IPCC paper:

  • The RCPs should not be interpreted as forecasts or absolute bounds, or be seen as policy prescriptive…
  • The socio-economic scenarios underlying the RCPs cannot be treated as a set with an overarching internal logic… [but note, that the IPCC nevertheless plots them all on the same graphs!]
  • The socio-economic scenarios underlying each RCP should not be considered unique. Certain characteristics of individual RCPs may play a role in interpreting their results, [for example] The logic for the land-use patterns is related to the model-specific assumptions of each RCP and not just to the target radiative forcing level. Climate policy may have clear consequences for land-use patterns, but these have been included in RCPs in different ways. For instance, the reforestation policies assumed in the RCP4.5 might also be possible in RCP2.6. Similarly, the assumed baseline trends in land use are not specific to any RCP level. Climate impacts of the land-use patterns (such as albedo), therefore, cannot be directly attributed to the level of climate policy in each RCP, but need to be traced to model-specific assumptions…
  • There are uncertainties in the translation of emissions profiles to concentrations and radiative forcing… As a result, the current set of RCPs represents one possible set of assumptions with regard to this translation. As the RCPs are used as input in all major global climate models, some of these uncertainties will be revealed as part of the activities that are currently under way. Further coordination of uncertainty analyses in subsequent phases by the climate modeling community and IAM community may further contribute to this…

I’m not sure whether this paper it has any significance outside the IPCCs matryoshkya-doll modelling frameworks; I’m ready to doubt that it does.

Finally, two things that strike me as odd—even suspicious—about the reported results:

  1. The extremely low level of hydrocarbon and nuclear use and very high level of “biofuel” use in the highest-income/lowest-emission profile. I wonder what “adjustments” have been made to relative prices in these models to produce such an energy mix? Typically, the IPCC is not saying: “… socio-economic parameters have not been included in the RCP information available for download” according to the paper.
  2. How the highest income scenario—mysteriously—could have the lowest energy-intensity of production, the second-lowest primary energy use, the highest use of “carbon-capture” technology (in fact, a negative emission of carbon per average unit of energy in later years) and a population growth trajectory that is the actual population trajectory is a mystery to me.

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