On May 17, 12:03 am, James Annan <[EMAIL PROTECTED]> wrote:
> Michael Tobis wrote:
> > Sure. I agree with that summary but don't see how to turn it into a number.
>
> > I believe that the climate risks are already large enough that we
> > should choose the lowest target which makes the economic risk of
> > disaster small.
>
> Are you referring to the "disaster" of AGW or the "disaster" of cutting
> emissions?
Sorry, I could have been clearer by swapping two words: We should
choose the lowest CO2 target which makes the risk of economic disaster
small.
Admittedly this is a crude constraint, probably insufficient to drive
a formal optimization.
That said, I think the name of the game is disaster avoidance, not
cost avoidance. We are going to incur some costs. Our objective should
be stated in terms of sustainability; we want to avoid the largest and/
or most abrupt declines in well-being.
> > I think this should be roughly expressed in terms of
> > peak CO2 concentration in practice, and that would appear to be in the
> > neighborhood of 500 ppmv, assuming the carbion cycle feedbacks don't
> > decide to bite with a vengeance.
>
> > I don't put much stock in the 2 C number except to say it is the best
> > estimate of the outcome of the lowest peak we can achieve, barring
> > some unforeseeable technological fix.
>
> I think the problem is best considered as one of (continuous and
> adaptive) optimisation, rather than "minimise emissions at all costs".
I agree in principle. A couple of points are relevant, which makes
your statement nearly equivalent to mine, in my view.
> Furthermore, although it is sensible to bear in mind the long-term
> outcome, I'm not convinced that the best approach is to build a strategy
> around a "target" CO2 level in 2100-2150.
The general principle is sound, but I think there is good reason in
the case of carbon accumulation to implement a long-range policy on
current evidence.
First of all, policy is a very blunt instrument, not an ensemble
Kalman filter. (Most readers will not even know what I am talking
about...) The point is that the optimization has to be performed in an
environment where the grasp of statistical methods is very weak. I
think the public understands probability better than they are given
credit for. Most people can play poker passably well. However,
adaptive optimization doesn't really map onto games of chance very
well, and it's a tall order to implement such a thing using the
mechanisms we have. As a consequence, the optimization will have to be
performed offline and passed as a recommendation to the policy sector.
This can be done adaptively, but the adaptation will not be
instantaneous. In fact, policy will necessarily match the best advice
of a few years previous.
The effect of irresponsible denialists and irresponsible alarmists
alike is to inject noise into the observation system, which means the
response of the controller will continue to be especially sluggish. In
a sense, the more public attention there is to the subject, the less
effective the communication of genuine expertise will be, and the less
responsive the policy sector, viewed as a control system, will be to
new input.
We aren't running entirely open loop, but for present purposes we
might as well be. This is why setting an explicit set of constraints
on CO emissions (very much in the spirit of engineering tolerances:
not to exceed a certain rate, or a certain maximum, to asymptote to
within a certain range of a certain final value...) is sensible.
Secondly, the idea that no constraints whatsoever, surely the easiest
outcome for the policy sector to achieve, constitutes "conservatism"
has been successfully promulgated by the more successful branch of
noisemakers. Consequently, the policy is currently very far from the
optimum that a sensible control system for a sensibly controlled plant
would achieve. If our behavior were middling-muddling, we could talk
about the sort of fine-tuning you imply.
At the moment, though, after twenty years of ignoring advice, we have
moved from a relatively manageable problem to a rather serious one,
and show every sign of moving to a range where the risk of cataclysmic
catastrophe is not negligible. We need to overcome a systematic bias
that has been built into policy. The possibility of historically
unprecedented abrupt global decline is what needs to drive the
discussion, and the failure to account for it means that vigorous
action is required.
It is, of course, no good avoiding a CO2-driven catastrophe by
creating an economics-driven catastrophe. There are other horsemen of
the apocalypse waiting in the wings as well. The problem is that there
is a new horseman on the scene, and it is past time to start giving
him his due. The longer we delay, the narrower the chance of keeping
the one at bay without leaving openings for the others.
mt
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