CO2 scenarios again

Posted by William M. Connolley on May 17, 2006
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Stoat, the blog that has abandoned science in favour of economics, about which I know little. But wait for the musing post on model skill scores…

Anyway, the last post got lots of interesting comments – thank you – dear reader, go take a look if you don’t normally read post comments. I shall pick up on a few of them…

The main issue is how much interaction should there be between economics and climate folk in constructing CO2 scenarios.

Currently, the IPCC (and many modelling groups) use the SRES scenarios. Or rather, in practice, only a few of the many scenarios. I (and possibly they, if pushed) would justify this by the scale-to-CO2-not-time argument (this is pretty well admitted by the practice of using much simpler models to interpolate between scenarios), but it has to be admitted that if you care about T rise at a given time this leaves something to be desired. SRES are constructed by… well I don’t know. I’m pretty sure lots of them are economists, since they are capable of saying things like “PPP” and sounding sensible. So I think that economists *are* involved in producing SRES. Maybe not the right ones? Some people clearly feel left out.

There are plenty of other scenarios out there but I don’t think many people bother with them. In some ways this is a fight for mind-share.

There is (as far as I know) little or no impacts-of-climate-change on the scenario economics – which was my reason for saying keep the econ and the sci separate. However, perhaps thats rather backwards looking: JA may be right to point out that you *expect* climate change to impact society, or else, errr, why are you bothering?

Some of the models are run with bio feedbacks – HadCM3s famous dieback of the amazon, for example. But these are (I think) only natural feedbacks. There is no “increased T in the tropics leads to more air conditioning but inc T in the poles leads to less heating” stuff in there. And thats only the bleedin’ obvious sort of econ feedback (less sea ice in the Arctic saves on fuel costs for shipping?). So perhaps there should be some economists involved in building feedbacks into the model? Perhaps, but thats not the same thing as scenario development. But I suspect that a model with those kind of feedbacks in would be rather hard to build well.

All in all I’m still somewhat dubious about the useful scope for clim/econ interaction… but maybe I’m just being fuddy-duddy. I’m also somewhat dubious about the value of this pile of ramblings, but since I’ve written it I’ll post it anyway :-)

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Comments

  1. #1 Dave Munger
    2006/05/17

    I’ve written an article for Seed that addresses some of these points — should be up within the next week or so. I’ll let you know when it’s out.

    [Please do! -W]

  2. #2 Jon
    2006/05/17

    Well, I’d like to make a non science based prediction. CO2 & Global Warming will create ever greater Dust Bowls in the Gobi desert, the Sahara, and Arizona deserts, before it causes any Artic or Antartic ice cap melting. So it will be mainland China (as far as Shanghai), northern Africa, and mainland US which will first feel the wrath of Nature. Factor that into any land economy & crop outputs.

    .

  3. #3 MattXIV
    2006/05/17

    Part of the problem is that any models complex enough to accurately represent economic feedback from increased temperatures would not be reliable on the time scale where AGW becomes a significant problem. Could you imagine a similar model devised in 1976 holding up today?

    [The easy answer is "no", which is why I'd tend to prefer just "CO2 inc by x% per year" with x about... 0.8? I can't see how such a model could easily be made reliable and useful... but maybe one can say the same of coupled O-A gcms, to some extent! -W]

  4. #4 Eli Rabett
    2006/05/17

    The answer to your question, of course, is, what is your purpose?

  5. #5 Q
    2006/05/18

    “Like sausage, the populace has no stomach for seeing how it is made.”

    Recognise your own quote Chairman Eli. I guess Climate Change as well as Demographic change can & do often run pretty much in parallel.

    Some people move to where there is work (economic migrants)
    Some people move away from lesser folk (eli-tist migrants)
    Some people move for land & property (invader migrants)
    Some people move to avoid floods or plagues (GW migrants)

  6. #6 Dave Munger
    2006/05/18

    The article is up now. Maybe a little oversimplified, but the gist is that economic projections aren’t very reliable, so you have to adjust them as you go along.

  7. #7 Eli Rabett
    2006/05/18

    Actually Q, that’s Chancellor Rabett, as in Otto von Bismark. And, btw, you left out a lot of people die, as, for example in irish potato famine and other ecological disasters.

  8. #8 Q
    2006/05/18

    Hi Eli, I was trying to be brief (rather than comprehensive). But yes I’ll grant you that the irish potato famine & the ethiopian famine (as well as others) were ecological disasters. Some would say man-made (politico-economic) ecological (and human) disasters.

    The floods, which prompted George Harrison’s concert (and film) for Bangladesh (the first Live Aid?), The South East Asian Tsunami, The Pakistan earthquake, all events which somehow dull people’s senses.

    I guess that is why so many Americans from the US, so used to Cyclones in the Gulf of Mexico, Tornadoes, flashfloods, snowstorms & chaotic weather elsewhere, think they are so resilient, they plough & plow on regardless, and find it so difficult to grasp the concept of cause & effect, or Climate Change.

    .

  9. #9 Q
    2006/05/18

    Dave, maybe they should have uk gas (petrol) prices in the US. In the UK petrol taxes (bumper revenues for the Treasury) are used to pay for pensions and the nhs (as well as roads & subsidies for public transport). The Chancellor reduced Road Tax on smaller vehicles (and added a pittance to 4X4s) as an incentive to ‘conserve’

    So perhaps the US (and elsewhere) need to bite the bullet, increase taxes on gas(oline) to EU levels first, and then the incentives to more efficient/alternative vehicles will not be so damaging to revenues needed for roads. Road Tax should (could) pay for roads. Fuel Tax could (should) pay for Environmental improvements… and so on.

    .

  10. #10 Eli Rabett
    2006/05/20

    Q is half right. There are two ways the US could go. The first would be to mandate fleet mileage limits, but as we have seen this is a game that the auto companies play, the second would be EU level taxes on gas. Since the latter are regressive that must be accompanied by equivalent cuts on payroll taxes which are regressive. The net effect would be slightly progressive. If accompanied by lifting of the maximum earnings on which Social Security taxes are levied the effect would be to make the total tax system much more progressive, increase revenues and solve the Social Security funding issue into the far future.