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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