Or perhaps its like a cryptic crossword clue and the “semi” refers to the word “analytic” itself. In this case it is more economical, and indeed more descriptive, to refer to them as “anal” models.

But all the government stuff is public domain, so you can look it up yourself if you like.

Note that since the American people own the source code, you can freely dl that and really get into it, should you so desire:
http://www.giss.nasa.gov/tools/

And most climate modellers are physicists. That’s what makes them so insufferable.

Hansen, J., G. Russell, D. Rind, P. Stone, A. Lacis, S. Lebedeff, R. Ruedy, and L. Travis, 1983: Efficient three-dimensional global models for climate studies: Models I and II. M. Weather Rev., 111, 609-662

I think if you want to cast doubt on people’s work and demand some kind of high level review, it would help to do some more homework and not rely on anecdotal evidence.

I totally agree. Like I’ve said before I didn’t expect to convince anybody by the tidbits I mentioned on this thread. I only included them to give people a feel for the types of things I was worried about, to see if there was anything parallel in this galaxy formation case. This whole thread is part of doing my homework.

-Sam

This is very optimistic. At some level, all simulation codes are similar: you have a bunch of PDEs and are approximating them with a finite difference scheme. On the other hand, the devil is in the details. Have you ever written a CFD simulation code or tried to use, test, and verify one? I did for my thesis and it took me an entire year to get to the point of trusting it, even though I started by adopting almost wholly a code someone had already written, and even though the code was primitive by modern standards and solved a highly simplified CFD problem. I would not expect to be able to vet someone else’s code in a different field without a huge effort. People in different fields need to make entirely different sets of approximations, so for example the techniques used in CFD in astrophysics can be very different from those used in atmospheric studies or oceanography. Also, particle physicists, bless their hearts, are not all competent to teach fluid dynamics, which is widely regarded as a scary nonlinear subject, and worst of all, applied science.

when a graduate student mentioned to me the sensitivity of that model to a change in the way vegetation is handled

I think if you want to cast doubt on people’s work and demand some kind of high level review, it would help to do some more homework and not rely on anecdotal evidence.

Some useful, non-technical summaries of the history of climate modeling can be found at
http://www.aip.org/history/climate/simple.htm
http://www.aip.org/history/climate/GCM.htm
I strongly recommend the whole site
http://www.aip.org/history/climate/

Makes sense… I suppose I should always be explicit in sensitive matters. Let me mention for the sake of further harmony and agreement that should an engineer (or even a biologist!) also have experience with complicated simulations, I’d want that person’s opinion, too. I’m not sure about a social scientist, however (me physicist so smart definitely no need whatever they do).

BTW Julianne (I think) wrote a really funny post on this a while back… the punch line was how we love to talk about bioligists, enginners, chemists… but we never mention mathematicians because we secretly fear they are smarter than us .

-Sam

This is a much more nuanced explanation of your concerns than what you wrote above. The comment which pushed my button really reeked of “Me physicist so smart I figure it ALL out myself!” This is an attitude which some physicists certainly give off, and drives my non-physicist science colleagues absolutely crazy.

scott

I don’t think this is correct, but it would certainly make me feel better about the whole field if it were. My understanding is that the temperature increase from man-made c02 would be negligible without the many poorly understood feedbacks, which must be simulated (and some still can’t be, such as cloud cover changes).

However I should say that if your sentence does turn out to be correct, then, as honest scientists, that is what we should tell Congress. Instead, we have Hansen presenting his model predictions with dramatic errorbarless increases out a hundred years, or giant international bodies putting uncertainties on numbers from simulations that, in line with your above sentence, we know just aren’t useful.

-Sam

The expertise of physicists that I refer to is a familiarity with what level of quantitative significance should be ascribed to results from complicated models, given what tests on those models are applied. For example, when a graduate student mentioned to me the sensitivity of that model to a change in the way vegetation is handled, my immediate reaction was “why should I believe anything that has ever come out of these models, or anything that will come out of them in the future, until they demonstrate that their results converge on some value as they add more and more physical processes?” Isn’t that your reaction, too?

All I hear in physics and astronomy colloquia and discussions is how (complicated) simulations are sometimes nice to have around but can’t be trusted quantitatively. I can’t count how many times somebody starts a sentence about their work or idea with “if you believe simulations…”. So, we don’t trust simulations. Then I hear the climate pepole talking about their simulations, which are immeasurably more coupled, non-linear, and tuned/made up, so I suggest that maybe we shouldn’t believe those, either. Maybe we should even be purportionaly more distrustful of those. At this point, somebody starts talking about Kyoto, or the oil companies, or tells me what some other “skeptic” once told them, as in this thread. But I just want to know why we trust simple N-body simulations and the most complicated non-linear systems ever attempted, but nothing in between. It doesn’t make any sense to me. Do you at least see where I’m coming from?

(By the way, I’d love to continue this in private some time, if you’re interested. It can be very frustrating in a group or online, but I was hoping to get Julianne’s opinion, so I posted.)

-Sam