Re: OT: interesting global warming quote found elsewhwere

On Aug 1, 2:55 am, James Arthur <bogusabd...@xxxxxxxxxxx> wrote:
bill.slo...@xxxxxxxx wrote:
On Jul 31, 4:49 am, James Arthur wrote:
bill.slo...@xxxxxxxx wrote:
On Jul 30, 11:37 am, James Arthur wrote:
bill.slo...@xxxxxxxx wrote:
On Jul 29, 4:19 am, James Arthur wrote:
On Jul 26, 5:40 pm, bill.slo...@xxxxxxxx wrote:
On Jul 26, 1:31 pm, James Arthur wrote:
<snip>
Your chaotic weather systems are unpredictable, but they deliver
roughly the same sort of statistical distribution of weather from year
to year, and you can model them well enough as statistical
distributions.

Sure, there's a long-term trend to climate: it's getting warmer, and
has been for nearly 20,000 years:
http://www.museum.state.il.us/exhibits/ice_ages/images/laurentide.mpg
Shortly before the trend was for cooling.  But those models were
proved wrong. :-)

Sure. We should be headed back towards the next ice age by now, but
pre-industrial anthropogenic global warming seems to have over-ridden
the small orbital forcing
http://en.wikipedia.org/wiki/Milankovitch_cycles
if William Ruddiman has got it right
http://en.wikipedia.org/wiki/William_Ruddiman
Your modeller's efforts freeze out the atmosphere and melt lead in the
same way that my LTSpice circuits occasionally produce megavolts and
mega-amps. This doesn't stop more carefully constructed models from
providing useful information.
You don't get it.
On the contrary, I get it rather better than you do.
You don't understand this person's position. I do.

Like your
informant, I too have worked on computer models (albeit at a pretty
primitive level, back in the 1960's as part of my Ph.D. project).
Your experience re: GCM is and can be in no way comparable.

But like you, I've modeled enough things to know the limits of
the technique, and can spy errors of technique and invalid
assumptions, especially when they're so obvious.

The
instability your modeller complained about isn't a fault of the model
as a model of the climate, but a fault of all models that rely on
numerical integration to step forward in time - which is why it shows
up in LTSpice models as well as climate models.
Now you presume to know the cause of the errors. How?

Read a couple of text-books on the subject back in the 1960's - it
isn't rocket science.

But how do you know today's weather models use 1960's techniques,
that they diverge from reality for the same reasons?

Physically realistic models of the atmosphere won't freeze the air or
melt lead unless the numerical integration process goes nuts, and that
integration process is central to all techniques of predictive
modelling.

Ahh, because you (reasonably) assume each phase of the simulation
takes the previous phase as input.  Errors, therefore, accumulate,
and are magnified by iteration.

With this and your comment upthread about how your LTSpice
simulations sometimes "produce megavolts and mega-amps,"
you acknowledge the problem of simulating the future.

All simulation processes can go wrong. If you are lucky, the errors
become obvious.

Fooling around with different step sizes can give you some idea of how
fast they will go wrong.

 This person works on *the* models.  Likely one
of the ones you base your beliefs on.  The comments re: instability
were directed at early GCM (global climate models) in general.
And applies generally to all evolving models - not just models of the
climate. Your informant wasn't too well-informed, or you didn't
appreciate what he was actually saying.
And this person opines the GCMs do not usefully predict
climate.

Clarification: the opinion was that GCMs do not usefully predict
events beyond a several-month timespan.  Under that, they're good
and getting better, but you'd call that "weather," not "climate."

Your second-hand report of his opinion on that aspect of their
performance doesn't strike me as decisive, given the preamble.
That report was based on actual testing of certain GCMs.

What I believe in is the physics on which they are based; that this
physics is applicable to the earth's atmosphere is fairly clearly
established by the ice-core data.

I also believe in physics.  The ice core data, though, establish
association, not causation.

As does all after the fact evidence.

I'm not particularly excited about
what the IPCC's favourite model says about the exact relationship
between carbon dioxide level and mean global temperature -

But the exact relationship is quite important--suppose it's all
true, but only amounts to 1ºC ?

what is
clear is that more CO2 means a warmer climate.

That is /not/ clear.  That's supposition until verified by experiment.
There are any number of reasons that might not hold, and none have
been tested.  Nor can all such reasons be anticipated.  That's why we
do experiments.

Name a few.

Suppose clouds become denser, more reflective, or more prevalent,
fending off another 1w / m^2 ?

Then we wouldn't have had runaway global warming in the geological
past.

Maybe they will, and maybe they won't.  You don't know that.

The question has been beaten to death - only the Exxon-Mobil funded
deniers and the people whom they have suckered still take this
particular propostion seriously. It's one of the red herring the ice-
core data has more or less killed off.

Maybe more water vapor in the atmosphere will affect heat transport
from equator to poles in some new and curious way, radiating heat
more effectively, or laying down ice albedo.

The "lot's more intense hurricanes" story is a case in point - the
intense hurricanes hypothetically drive more warm surface water down
into the dpeths of the ocean so the ocean currents transport more heat
to the polar regions.

Of course it would more or less render the tropics uninhabitable so it
doesn't exactly encourage us to push more carbon dioxide into the
atmosphere.

What is also clear is
that a warmer climate means warmer oceans in due course, which won't
hold as much CO2 in solution as they do now so we are eventually going
to get back that 30% of our contributions to atmospheric CO2 which is
currently being absorbed by the oceans, plus a certain amoint of
interest.

That's also supposition.  Plausible, but supposition.  You don't
know that.

Don't be silly. The solubility of carbon dioxide in seawater as a
function of temperature is thoroughly predictable.

For one thing, you're treating the earth like a wet rock,
projecting its future by how much CO2 dissolves in water.
That treatment ignores the very living, breathing force that
created the atmosphere and sequestered all that carbon to
begin with: life.

Sure, but we have the geological record of how "life" reacted to
higher and lower temperatures and CO2 levels in times past; the record
is spotty, but it isn't spotty enough to allow you or John Larkibn to
wave your hands and invoked some "unpredictable" saving mechanism.

For another, your treatment is qualitative, not quantitative.
If you can't tell the weight of the factors, you can't compute
their present sum, much less project future effects.

I know enough to be confident that the IPCC is doing an adequate job
on the quantitative estimates.

The only hope for simulation, btw, is if there's net negative
feedback which serves to constrain the accumulation of errors.
Like the resistor across an integrator's cap.

Or if it makes sense of the historical record.

And we know there is such feedback in the real system, else
we wouldn't be here.

There are a couple of global extinction events in the geological
record that have allowed us to be here, rather than some highly
evolved squid or crab. Not all the feedbacks are negative.

In short, we proceeding down a one-way street which is going to get
steeper and more slippery the further we go. At some point we run the
risk of destabilising the methane hydrates under the permafrost and
along the continental shelves - search on the "clathrate gun" for the
consequences of hitting that particular threshold.

http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

This link is aptly listed as a(n) hypothesis.

Sure, and your superior hyopothesis for explaining the same facts is?

Scientific rigor demands more than supposition.  Experiment has
vitiated countless promising theories, and

"If it disagrees with experiment, it's WRONG!" --Richard Feynman

Sure, but all scientific theories are hypotheses - equally vulnerable
to some imagined experiment - and it isn't "scientific" to throw out
the best available hypothesis because you don't like the predictions
it generates

There's little doubt in my mind that we're providing a carbon-impulse
to the earth's climactic system; what we don't know is the earth's
impulse response.  And the projections on partial information are
absurd.

The ice core data and the geological data - such as it is - does give
us some pointers the the earth's impulse response. That's what the
IPCC is playing around with at the moment, and - unsatisfactory as
their work may seem to you - it is still a whole lot more useful than
denying that we can make any kind of prediction.

You snipped me asking what evidence supported your faith in
models, but you've explained.

Your concerns are based on selected qualitative factors, the
net effect of which you cannot know--incomplete of their nature,
for one can never fully anticipate all the things that matter--and
rely on simplified computer models to iterate and project those
factors to create a reliable future scenario.

I'm not berating your concerns--they're rational.  AGW's worth
considering.  But the magnitude of its effects are proposed,
not fact.  And possibly saving us from an ice age, as you noted
earlier.  Would you risk throwing us into one with hasty action?

That doesn't seem to be at all likely.

--
Bill Sloman, Nijmegen
.

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