Michael Tobis again:
>By the way, a sudden decrease of *emissions* by some 80% is NOW required
>to hold CO2 *concentrations* to current levels.
Again what is the basis of this statement? The naive model
suggests a 50% reduction would suffice (assuming 50% of anthropogenic
CO2 has remained in the atmosphere).
James B. Shearer
Would someone knowledgeable please clear up this misonception that a new
ice age is _imminent_ (when I first heard that I already knew enough about
time scales to know that "imminent" means "in a few thousand years")?
There seems to be a mindset out there (I have heard several prominent
deniers state it, some with urgency) that we _need_ global warming in
order to ensure continued productivity of northern agricultural land
and to keep the planet out of a new glacial period. This is very, very
irresponsible, given our comparative lack of knowledge concerning the
details of climate change.
--
Gruss,
Dr Bruce Scott The deadliest bullshit is
Max-Planck-Institut fuer Plasmaphysik odorless and transparent
b...@spl6n1.aug.ipp-garching.mpg.de -- W Gibson
You, too, Shearer, like Bass, suffer from an unpurged havingness
in your being.
-dennis turner
I think this is a very relevant point which deserves a lot of discussion.
I asked a colleague who is very knowledgeable about decision theory
both from a theoretical and practical perspective. He pointed out
that since costs and benefits are not shared equally, this is not
a question which can be analyzed by the usual techniques.
I might use cost/benefit analysis as an individual in deciding to not
take a certain medication
because it may cost me a lot or have a lot of side effects and the
probability of its doing any good many be low. With a decision about
what our society should do, or even worse what humanity should do,
it is much more complicated. We don't all pay the same costs and we
don't all share the same benefits. One could of course try to
somehow integrate those factors over present and future
populations. However, that won't work very well for
a variety of reasons. For example, those in a position to make
the decisions may have to pay a very high cost with no real benefit
to themselves while those benfitting may not be in a position to
influence the decision. There may be a lot more of the latter than
the former, but still the decision may not be made.
However, despite my colleague's admonitions, I am not convinced
that one can't set up a rational framework to discuss these matters,
and I welcome discussion.
With respect to the issue of global warming, there have been some
discussions by economists about the virtues of waiting various
amounts of time before acting if indeed global warming does take
place. Needless to say the assumptions and modeling here are
in much worse shape than climate modeling, but still it would be
instructive to examine some of them. However, let's not take
any of them as proving anything conclusively one way or the other.
Leonard Evens l...@math.nwu.edu 708-491-5537
Dept. of Mathematics, Northwestern Univ., Evanston, IL 60208
I'll let this be my last posting on this subject.
Hahahahahahahahahahahaha.
dale bass
From the internal evidence of what you say in (1), it appears
that you are lacking
in knowledge about conventional decision theory.
In that theory, one uses the so-called expected gain which is the
sum of the probability of various outcomes multiplied by their
costs. Under sufficiently restricted conditions, this is a rational
thing to consider. Michael was trying to set up a rough model
along these lines. I would like see some further attempts to
quantify this, although as I remarked in an earlier posting,
there are some real problems with this.
Your other questions (2) and (3),
are quite reasonable and perhaps should be
addressed. As far as (4) is concerned, I think Michael would attach
very low probability to that, and I would agree with him.
He has presented arguments I find convincing that any trends towards
a new ice age operate on a longer time scale than that involved
in CO2 induced warming. In addition, this scenario is not a reason
for being complacent. It presents all sorts of serious questions
about which we know very little.
If indeed global cooling would otherwise be in the cards, it would
occur at some rate, and it may not be very linear, as Dale Bass
and other critics of global warming predictions point out.
There would be three possibilities: cooling would be swamped by
the CO2 induced warming, vice versa, or they would just happen to be
roughly in balance. The last possibility seems to me to be
the least plausible, unless you are arguing that an intelligent
hand is somehow guiding all this (God? Gaia?) Finally,
if there is global cooling going on, it must be the result of
some physical mechanism, not currently understood, and there
is no particular reason to believe that we couldn't
have a rough balance in average global temperatures but still have
rather dramatic changes in global and regional climates.
Hence, if you really believe this might be happening, you should
become a partisan of intense climatological research looking for
answers as quickly as possible, both on theoretical models and
observational data. The results of such research might not
be completely definitive and might suggest actions (like say
increasing CO2 emissions) based on less than total information.
Michael is talking basically about what
happens in the next hundred years or so. The effective `residence time'
of CO2 (although that is not accurate in the usual sense) is
estimated by the IPCC Report and Supplement to be something like
120 years. So your naive model is too naive.
> 4. Is the best plausible outcome no effect? What
>probability would you assign to the following scenario? Anthropogenic
>CO2 prevents another ice age.
If we continue our current path, quite possible. However, since there
is little reason to expect natural causes to initiate another ice age for
a few more thousand years, we have a lot of other things to place a
priority on in the meantime.
--
Dave Halliwell
Department of Geography
University of Alberta
Edmonton, Alberta
I didn't say it would be easy.
What I do say is that the rosy scenario so often propounded as plausible in
fact relies on a large number of unknowns all turning out in a way that is
most favorable. In practice, such scenarios require not only that global
warming be small, but also that whatever (entirely speculative) process it
is that ends up raising the planetary albedo (to compensate for the decreased
atmospheric transparency to the infrared) itself have no major deleterious
impacts. In other words, such a scenario, while barely plausible, is not
particularly likely.
Accordingly, it should carry equal weight in our calculations with a scenario
that has a number of unknowns all going unfavorably. Suppose initial worries
about the stability of the Ross Ice Shelf, now considered centuries away
from collapse, turned out to be valid. Suppose warming in the Arctic really
were sufficient to release huge quantities of methane in a positive feedback.
Suppose high cirrus formation (which has a warming effect) were enhanced.
What a mess. Say this yielded a climate sensitivity of 6 C, and a long
term response to unconstrained emissions of 12 C in the global mean.
Then consider the best estimate that sensitivity will be about 2 C (I'm
being generous), and final response will be a 4 degree warming.
Which of these scenarios should figure most prominently in our calculations?
Well, it depends on the cost of the contemplated response.
Suppose the impact of the first scenario were negligible, the middle scenario
about a trillion dollars, and the last about a quadrillion (essentially
wiping out most existing wealth). Suppose the cost of mitigating the last
scenario were ten trillion, while that of mitigating the middle scenario
were a hundred billion.
Suppose the probability of the first scenario were 40 %, the middle scenario
50 % and the last scenario 10 %. This is a much more *optimistic* picture
than that currently yielded by the science but it illustrates my point.
Let's call the best, middle and worst scenarios A, B and C, and the response
strategies a b and c
EXPECTED COST
strategy -> a b c
scenario
A (40 %) 0 10^8 10^10
B (50 %) 10^9 10^8 10^10
C (10 %) 10^12 10^12 10^10
expected
cost 10^11 10^11 10^10
Thus, if strategy had to be determined entirely in advance, the rational
choice would be dominated by the MOST SEVERE plausible outcome, even though
it was unlikely. (These numbers, again, are completely fabricated, intended
to give the general idea only.)
Of course, there's not only a continuuum of scenarios and a continuum of
responses, there's also a continuum of WHEN the various responses are
put into effect.
If John McCarthy's argument that costs of response declines as the world
becomes more adept dominates over my argument that abrupt responses, and
particularly abrupt reductions in emissions, are more expensive than gradual
responses, and particularly cessation of *growth* in emission rates, then by
all means we should do nothing until it is absolutely necessary.
The problem is that it may be absolutely necessary to respond to the more
unpleasant cases long before the fact that they hold is proven! This is
because there is evidence that the system has a substantial lag time.
An actual mathematical solution of the resulting optimization is not
feasible, but those are the main sorts of factor that need to be weighed
even before the political realities are contemplated.
There is much to be said for limiting emissions to approximately current
levels. In doing so, only new energy uses will have to account for the
new limitation, and the economic impact, while large, will not be huge.
If this limitation turns out to be excessive, it may be reversed. (Yes I
know such reversals have political problems, too.) In doing so, we may
limit the forcing to doubling of CO2 equivalent. I remind you all that
quadrupling is by no means implausible by the end of the next century.
In any case, there's an awful lot here that's extrinsic to climatology,
and on these matters I speak entirely as a layman.
mt
I believe you are correct in this matter. Allow me to improve my statement.
The final concentration seems likely to be very sensitive to the TIME
at which emissions stop increasing, if we assume that sudden decreases
in emissions are unlikely. This is because emission rates are rising
rapidly and have only recently begun to reach levels of significant impact.
Incidently why are sudden decreases unlikely? It
|> would seem to me that emissions are likely to decrease at least as
|> fast as they rose as fossil fuel supplies are exhausted.
Coal supplies are not likely to be exhausted. There's enough proven coal
reserves to increase atmospheric concentartion of CO2 by roughly an order
of magnitude.
It's generally believed that since so many processes contribute to greenhouse
gas accumulation, in so many societies and systems, that rapidly changing
these emissions will be very difficult and expensive. Beyond that, I'm not
competent to say much.
Suppose you had to halve your personal contribution to emissions tomorrow.
Could you comply?
|> Michael Tobis again:
|> >By the way, a sudden decrease of *emissions* by some 80% is NOW required
|> >to hold CO2 *concentrations* to current levels.
Let me say that this number shouldn't be relied on too much. It's vaguely
remebered from a graph in the beginning of the 1990 IPCC document, which
I finally had to give back to the library.
|> Again what is the basis of this statement? The naive model
|> suggests a 50% reduction would suffice (assuming 50% of anthropogenic
|> CO2 has remained in the atmosphere).
I don't see how this follows. To each emission level there is, roughly
speaking, an asymtpotically approached final concentration.
Current emissions equilibrate at a bit above double CO2 background, while
current concentrations are at around 25% above background. (Again, numbers
off the cuff with no documentation, but they seem about right to me.) So the
linear model you propose above would imply a reduction by a fator of about 5.
mt
mt
===
I get the following figures - or isn't an American trillion
equal to 10^12, a quadrillion to 10^15 ?
strategy -> a b c
scenario
A (40 %) 0 10^11 10^13
B (50 %) 10^12 10^11 10^13
C (10 %) 10^15 10^15 10^13
expected
cost 10^14 10^14 10^13
Also, some readers maybe didn't understand that
a = do nothing
b = countermeasures sufficient to mitigate scenario B
c = countermeasures sufficient to mitigate scenario C
===
|> |> Again what is the basis of this statement? The naive model
|> |> suggests a 50% reduction would suffice (assuming 50% of anthropogenic
|> |> CO2 has remained in the atmosphere).
|>
|> I don't see how this follows. To each emission level there is, roughly
|> speaking, an asymtpotically approached final concentration.
|>
|> Current emissions equilibrate at a bit above double CO2 background, while
|> current concentrations are at around 25% above background. (Again, numbers
|> off the cuff with no documentation, but they seem about right to me.) So the
|> linear model you propose above would imply a reduction by a fator of about 5.
On second thought, this seems like nonsense to me and your argument
seems perfectly valid. I withdraw the whole business. Reducing emissions
by 50% would probably suffice to stabilize concentrations. I realized this
in embarassment verging on terror after I went home last night.
It seems my postings are not 100% reliable. On the other hand, unlike
some people, I am willing to admit when I have been babbling nonsensically!
mt
j...@watson.ibm.com writes:
> 4. Is the best plausible outcome no effect? What
>probability would you assign to the following scenario? Anthropogenic
>CO2 prevents another ice age.
If we continue our current path, quite possible. However, since there
is little reason to expect natural causes to initiate another ice age for
a few more thousand years, we have a lot of other things to place a
priority on in the meantime.
Hmm, some questions.
What is the current thought on the "causes" for the little ice age?
What about the end of the little ice age?
Is the Atlantic Conveyor unstable or not? If the Gulf Stream bend
moves south (which may occur on a very short time scale in principle)
the Northern Europe permanent snow line will move rapidly south,
albedo will increase providing a stabilising feedback to the cooling.
Is any Gulf Stream instability likely to be more sensitive to a cooler
or warmer Northern Hemisphere? - If the Gulf Stream is unstable at
warmer climates, how do we enter a stable ice age?
What is the current thought for regional climate variability
rates during ice age transitions? My impression from a cursory
reading of the literature was that degree/decade or more rapid
variations were not uncommon during ice age onset and termination
on scales of continental areas?
What was the mean temperature during the golden age of the mid-east
compared to now? Say around 4000 AD?
* Steinn Sigurdsson Lick Observatory *
* ste...@lick.ucsc.edu "standard disclaimer" *
* I know people whose idea of fun *
* Is throwing stones in the river in the afternoon sun *
* Oh let me be as free as them *
* - BB 1986 *
|> >Should we really be focussing on the *most likely* outcome? Are we doing so
|> >because so many people focus on the *best* plausible outcome and we feel a
|> >need to rebut them? Shouldn't cost-benefit assessments take the *worst*
|> >plausible outcomes into account as well?
|> I believe things are not so simple as you suggest above. I
|> have the following questions.
|> 1. The above appears to assume that outcomes should be
|> arithmetically averaged. Why is the arithmetic average to be
|> preferred to the geometric average?
|> James B. Shearer
I didn't say it would be easy.
...
Accordingly, it should carry equal weight in our calculations with a scenario
that has a number of unknowns all going unfavorably. Suppose initial worries
about the stability of the Ross Ice Shelf, now considered centuries away
from collapse, turned out to be valid. Suppose warming in the Arctic really
were sufficient to release huge quantities of methane in a positive feedback.
Suppose high cirrus formation (which has a warming effect) were enhanced.
What a mess. Say this yielded a climate sensitivity of 6 C, and a long
term response to unconstrained emissions of 12 C in the global mean.
This is in strong contradiction to paleoclimate tracks, as I
understand them. CO2 concentration has been several times higher
in the geologically recent past with temperatures 3-6 degrees higher.
We also had extensive ice ages during CO2 levels > 2 times larger than
current, but that was far enough back the continental configurations
were radically different.
Then consider the best estimate that sensitivity will be about 2 C (I'm
being generous), and final response will be a 4 degree warming.
Which of these scenarios should figure most prominently in our calculations?
Well, it depends on the cost of the contemplated response.
You have to be careful when considering extreme outcomes.
A comparable issue is the question of how much effort we should
expend on defending the Earth from asteroid and comet impacts.
There is a 3\times 10^{-7} - 3\times 10^{-8} probability per
year of an impact large enough to wipe out humanity. Expected
cost is infinite. How much effort should we expend to prevent this?
I presume that was meant as a rhetorical question, but it does require
an answer. Certainly, we should do more than nothing about this
problem. At the very least, we should make a fairly serious attempt
to monitor bodies which might collide with the earth. That won't
cost very much and very likely will have benefits beyond its initial
purpose.
Also, Michael Tobis was not discussing events with such a low
probability. I think he would attach a probability, say to a 6 deg
sensivity to doubling amd ulitmate temperature rise of 12 deg
as greater than 1/100. In most
human activities, we take high cost risks of that magnitude very
seriously. For example, despite the well known link between smoking
and lung cancer, the great majority of smokers don't die of lung
cancer. A more comparable
matter would be runaway greenhouse warming a la Venus. The probability
is so low that despite the very high cost, there is no sensible way
to incorporate it in our decision making.
What was the mean temperature during the golden age of the mid-east
compared to now? Say around 4000 AD?
^^!
Bummer!
Well, if you can tell me that I'll be real impressed. But how about
4000-2000 BC instead...
In article <STEINLY.93...@topaz.ucsc.edu> ste...@topaz.ucsc.edu (Steinn Sigurdsson) writes:
>In article <1993Nov26.0...@cs.wisc.edu> to...@skool.ssec.wisc.edu (Michael Tobis) writes:
> Then consider the best estimate that sensitivity will be about 2 C (I'm
> being generous), and final response will be a 4 degree warming.
> Which of these scenarios should figure most prominently in our calculations?
> Well, it depends on the cost of the contemplated response.
>You have to be careful when considering extreme outcomes.
>A comparable issue is the question of how much effort we should
>expend on defending the Earth from asteroid and comet impacts.
>There is a 3\times 10^{-7} - 3\times 10^{-8} probability per
>year of an impact large enough to wipe out humanity. Expected
>cost is infinite. How much effort should we expend to prevent this?
I presume that was meant as a rhetorical question, but it does require
an answer. Certainly, we should do more than nothing about this
It was a rhetorical question, but one with a basis in reality,
and incidentally one of current concern. I was pointing out that
we typically do not evaluate high risk-low probability events
rationally, we systematically under-emphasise some and over-emphasise
others.
problem. At the very least, we should make a fairly serious attempt
to monitor bodies which might collide with the earth. That won't
cost very much and very likely will have benefits beyond its initial
purpose.
Well, $10^7/year is sort a minimum effort. You can easily go up
a lot from there.
Also, Michael Tobis was not discussing events with such a low
probability. I think he would attach a probability, say to a 6 deg
sensivity to doubling amd ulitmate temperature rise of 12 deg
as greater than 1/100. In most
Is that right Mike? :-)
human activities, we take high cost risks of that magnitude very
seriously. For example, despite the well known link between smoking
and lung cancer, the great majority of smokers don't die of lung
cancer. A more comparable
matter would be runaway greenhouse warming a la Venus. The probability
is so low that despite the very high cost, there is no sensible way
to incorporate it in our decision making.
Oh, no, not that one again... don't you know what daemons you
can conjure with such words! ;-)
* Steinn Sigurdsson Lick Observatory *
* ste...@lick.ucsc.edu "standard disclaimer" *
* The laws of gravity are very,very strict *
* And you're just bending them for your own benefit - B.B. 1988*
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From: ste...@topaz.ucsc.edu (Steinn Sigurdsson)
Newsgroups: sci.environment,sci.physics.fusion
Date: 28 Nov 93 14:49:09
Organization: Lick Observatory/UCO
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<STEINLY.93...@topaz.ucsc.edu>
NNTP-Posting-Host: topaz.ucsc.edu
The temperature of the earth in 4000 AD will be whatever humans want
it to be.
--
John McCarthy, Computer Science Department, Stanford, CA 94305
*
He who refuses to do arithmetic is doomed to talk nonsense.
_Which_ humans, Mr. McCarthy?
-Alexey Merz
ps- How about 1 K?
|> The temperature of the earth in 4000 AD will be whatever humans want
|> it to be.
This is not unlikely.
I note that Dr. McCarthy regularly argues in favor of deliberate global
climate modification and against world government. I see his points as
worth considering in both of these matters but wonder how they can possibly
be consistent.
In any climate modification scheme, there will be winners and losers (unless
the modification is so severe that there are losers only). How can losing
nations be adequately consulted and compensated in the absence of a global
authority of some legitimacy?
mt
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From: to...@skool.ssec.wisc.edu (Michael Tobis)
Newsgroups: sci.environment,sci.physics.fusion
Date: 29 Nov 93 18:05:42 GMT
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This is not unlikely.
mt
Yep, it's a problem. I suppose there can be a limited grant of
authority to a climate authority in matters concerning climate.
>> I believe things are not so simple as you suggest above. I
>>have the following questions.
>> 1. The above appears to assume that outcomes should be
>>arithmetically averaged. Why is the arithmetic average to be
>>preferred to the geometric average?
>> 2. What is the function we are maximizing?
>> 3. What is the definition of a "plausible" outcome?
>> 4. Is the best plausible outcome no effect? What
>>probability would you assign to the following scenario? Anthropogenic
>>CO2 prevents another ice age.
>> James B. Shearer
> .. . . The results of such research might not
>be completely definitive and might suggest actions (like say
>increasing CO2 emissions) based on less than total information.
Leonardo, It's not that one needs TOTAL information, it's that
one needs reasonably consistent and COMPLETE information.
Understand the difference ??
>Leonard Evens l...@math.nwu.edu 708-491-5537
>Dept. of Mathematics, Northwestern Univ., Evanston, IL 60208
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