Two reasons for caution in climate mitigation

Ross Gar­naut says that he now believes cli­mate change to be ‘a worse and more urgent prob­lem’ than he believed before­he began his enquiry. Although his Inter­im Report (Sec­tion 2.1) accepts the IPCC pro­jec­tions only ‘on the bal­ance of prob­a­bil­i­ties’, it seems clear that Pro­fes­sor Gar­naut is per­son­al­ly con­vinced that the out­look for Aus­tralia is at least as bad as the IPC­C’s extreme A1F1 Sce­nario; that is, a warm­ing of more than 0.2c/decade for the first few decades of this cen­tu­ry. He is espe­cial­ly con­cerned by the high lev­els of car­bon emis­sions that have been pro­duced by spec­tac­u­lar growth rates in emerg­ing economies such as Chi­na. Accord­ing­ly, his Review’s Inter­im Report con­cludes that the evi­dence “sug­gests that it would be in Australia’s inter­ests to seek inter­na­tion­al agree­ment on the most ambi­tious fea­si­ble glob­al mit­i­ga­tion tar­get” (Sec­tion 3.2 of the Inter­im Report).

I am dis­ap­point­ed that the Gar­naut Review has so far accept­ed, with­out sub­stan­tial crit­i­cal analy­sis of its own, the most extreme sce­nar­ios devel­oped by the IPC­C’s mod­el­ers. A mod­el is an abstrac­tion that nec­es­sar­i­ly leaves out many fea­tures of the world (that’s its val­ue as a mod­el) . But sim­pli­fi­ca­tion qual­i­fies the pre­dic­tive pow­er of a mod­el’s pro­jec­tions. I am sur­prised that econ­o­mists such as Gar­naut (or Stern or Nord­haus, for that mat­ter) who are famil­iar with the frailty of com­plex mod­els of the econ­o­my seem inclined to accept the pro­jec­tions of cli­mate mod­els with­out care­ful­ly check­ing them against cur­rent obser­va­tions. There are strong rea­sons, I believe, for ques­tion­ing both the reli­a­bil­i­ty of the IPC­C’s mod­el-based pro­jec­tions of tem­per­a­ture trends and the car­bon-forc­ing the­o­ry that sup­plies the IPC­C’s mech­a­nism of man-made cli­mate change.

Reasons for questioning the temperature projections

The Gar­naut Review’s Inter­im Report con­fines its tests of the cred­i­bil­i­ty of the A1F1 sce­nario, for exam­ple, to a cou­ple of para­graphs and a cou­ple of low-res­o­lu­tion graph­ics that it takes from a 1‑page report by Rahm­storf et. al. pub­lished in the jour­nal Sci­ence in May 2007 that now appears to have been mis­tak­en. Rahm­storf and oth­ers claim that the observed tem­per­a­ture trends over the peri­od 1990–2006 were “the upper end” of the range of IPCC tem­per­a­ture pro­jec­tions for the 1990–2006 period—a con­clu­sion that the Gar­naut Inter­im Review adopts at Sec­tion 2.4. But the data on emis­sions and tem­per­a­tures in the IPCC reports for the peri­od 1990–2000 were fixed para­me­ters built into the SRES sce­nar­ios and not pro­jec­tions. In the IPCC Assess­ment Reports, only the trends pro­ject­ed beyond 2000 derive from the IPCC mod­els, which means that Rahm­stor­f’s assess­ments are based on 5 years of actu­al pro­jec­tions (2000–2006), not 16 years (1990–2006) and there­fore sub­ject, at a min­i­mum, to much greater degrees of uncer­tain­ty (see the dis­cus­sion of Rahm­storf et al. here).

The IPC­C’s SRES sce­nar­ios have not changed since their pub­li­ca­tion in 2000. They were not updat­ed (delib­er­ate­ly) for the 2007 Fourth Assess­ment Report in order to pre­serve their capac­i­ty to show vari­a­tions in out­comes due to dif­fer­ences in the sce­nario para­me­ters. Accord­ing­ly, data used to deter­mine para­me­ters for the sce­nar­ios such the A1F1 Sce­nario refer to the peri­od before 2000. The pro­jec­tions of the mod­els reflect­ing each sce­nario begin from 2000. The for­mer Aus­tralian Sta­tis­ti­cian, Ian Cas­tles, has con­firmed this fix­a­tion of the data from records of the prepa­ra­tions for the 2007 IPCC report. 

The sci­ence of cli­mate change must pro­vide test-able, that is fal­si­fyable, propo­si­tions to be sci­ence. Those propo­si­tions are found in the pro­jec­tions of the IPCC mod­els of tem­per­a­ture trends after 2000. Now Lucia Lil­je­gren has suc­ceed­ed in show­ing that those pro­jec­tions are wrong for the peri­od 2001–2008, dent­ing the cred­i­bil­i­ty of the IPCC mod­els and, a for­tiori, the Rahm­storf con­clu­sion (adopt­ed by the Gar­naut Inter­im Report) that observed tem­per­a­tures are “at the upper end” of the A1F1 pro­ject­ed range. 

Using sta­tis­ti­cal meth­ods that ensure robust regres­sion analy­sis of the tem­per­a­ture data time-series, Lil­je­gren has shown that trends in the observed tem­per­a­ture data from 2001 to 2008 diverge sig­nif­i­cant­ly from the IPCC pro­ject­ed trends, reveal­ing a decline in tem­per­a­tures at a rate of ‑1.1c/Century (as opposed to the IPC­C’s ‘mid-range’ pro­jec­tions of more than 2.0c/Century). Her care­ful analy­sis does not, as Lil­je­gren observes, show that the glob­al warm­ing has gone away (she is con­vinced that anthro­pogenic warm­ing is hap­pen­ing). Rather, they show that the IPCC pro­jec­tions don’t come even close to pro­ject­ing the tem­per­a­ture trends for the last sev­en years: that is for the peri­od since 2001 when IPCC pro­jec­tions began. If there is anoth­er upturn in tem­per­a­ture trends fol­low­ing this recent peri­od of shal­low decline, then con­cerns about warm­ing trends will look more cred­i­ble again. But the IPCC pro­jec­tions won’t be repaired by an upturn in tem­per­a­ture. What­ev­er hap­pens next, the IPC­C’s projections—and hence, their models—seem to need revision.

Lil­je­gren is not the only sta­tis­ti­cian recent­ly to fault the IPCC/SRES pro­jec­tions. David Stock­well, an ecosys­tem mod­el­er, has shown that a sim­ple lin­ear regres­sion of the tem­per­a­ture data over the past decade pro­vides suf­fi­cient rea­son to con­sid­er the IPCC pro­jec­tions ‘high­ly unlikely’

[T]he trend in tem­per­a­tures for the last 10 years is so low, that an increase of 0.2C per decade could be reject­ed in 3 out of 4 indices [That is, tem­per­a­ture series. PWG]with some lev­el of con­fi­dence. In one case, using the IPCC ter­mi­nol­o­gy, these results sug­gest IPCC pro­jec­tion of glob­al warm­ing this cen­tu­ry are very unlike­ly (1–10% chance) to be cor­rect. This is a con­tro­ver­sial result con­tra­dict­ing the IPCC ‘con­sen­sus’ posi­tion.” Niche Mod­el­ing

Reasons to question the carbon-forcing thesis

click for larger image

Although the Gar­naut Review makes no attempt seri­ous­ly to con­sid­er ques­tion the evi­dence for this the­o­ry, there is very lit­tle evi­dence (or none) of any cor­re­la­tion between the monot­o­nous growth in the CO2 con­cen­tra­tions in the atmos­phere and the vari­a­tions in glob­al tem­per­a­ture anom­alies. It does­n’t take much skill to dis­cov­er this as shown by the graph­ic (click the thumb­nail to see it full-size) that I cre­at­ed from pub­licly avail­able data. CO2 con­cen­tra­tions as mea­sured by the Scripps Oceano­graph­ic Insti­tute at Mau­na Loa, Obser­va­to­ry, Hawaii, have increase steadi­ly with pro­nounced but reg­u­lar sea­son­al vari­a­tions since they were first mea­sured in the 1960s. It is evi­dent that the CO2 trends look noth­ing like the low­er-tro­pos­phere (i.e. sur­face) tem­per­a­ture anom­aly trends (from RSS satel­lite data). Five min­utes with Excel (or a sta­tis­ti­cal pack­age such as R) shows that the cor­re­la­tion (r2) between the two series is non-exis­tent (see also this arti­cle by J D’Aleo).

This is only ama­teur obser­va­tion. Not proof of any­thing but ample rea­son to ques­tion the evi­dence for a the­o­ry that leads Pro­fes­sor Gar­naut to rec­om­mend a dra­mat­ic re-pric­ing of car­bon-based ener­gy pro­duc­tion in Aus­tralia. There is, also, more damn­ing recent data that seems to fal­si­fy the pre­dic­tions of the CO2 thesis

One of the key pre­dic­tions of the CO2-water-vapor fee­back-loop that dri­ves the green­house effect dom­i­nat­ing IPCC think­ing is that tem­per­a­tures in the tro­pos­phere (between 450 hPA and 750 hPA of atmos­pher­ic pres­sure) In the trop­ics should rise faster than sur­face tem­per­a­tures as ver­ti­cal con­vec­tion cur­rents dri­ve heat dis­tri­b­u­tion. This effect has been called the ‘char­ac­ter­is­tic emis­sion lay­er’ demon­strat­ing the water-vapor feed­back cycle that the CO2 emis­sions initiate.

Now a paper in the Inter­na­tion­al Jour­nal of Cli­ma­tol­ogy by Dou­glass et al. appears to demon­strate that this “char­ac­ter­is­tic” effect does not exist.

Mod­els are very con­sis­tent, as this arti­cle demon­strates, in show­ing a sig­nifi­cant dif­fer­ence between sur­face and tro­pos­pher­ic trends, with tro­pos­pher­ic tem­per­a­ture trends warm­ing faster than the sur­face. What is new in this arti­cle is the deter­mi­na­tion of a very robust esti­mate of the mag­ni­tude of the mod­el trends at each atmos­pher­ic lay­er. These are com­pared with sev­er­al equal­ly robust updat­ed esti­mates of trends from obser­va­tions which dis­agree with trends from the mod­els. The last 25 years con­sti­tute a peri­od of more com­plete and accu­rate obser­va­tions and more real­is­tic mod­el­ling efforts. Yet the mod­els are seen to dis­agree with the obser­va­tions. We sug­gest, there­fore, that pro­jec­tions of future cli­mate based on these mod­els be viewed with much caution. ”

Update :The data sets used in the Dougalass et. al. paper have been chal­lenged by the con­trib­u­tors to Real Cli­mate (26 March, 08)

1 Comment

  1. One of the great things about the Gar­naut report (and the Stern report in the UK) is that they are done by non-sci­en­tists. In oth­er words, if they had any bias­es per­ceived it might be in denial. At least they under­stand how sci­ence works and that there real­ly is an urgent need for action. One sug­ges­tion I’ve seen that cross­es the bound­aries of sci­ence, big busi­ness and eco­nom­ics is the adap­ta­tion of med­ical triage ideas to cli­mate — see for more infor­ma­tion. There’s lots of good ideas there that deserve a debate

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