#engineerilyderiving

What’s the corresponding situation with climate? It’s definitely not an engineering discipline at this point – we’re still in the frontiers of science. But some of the components are there, or at least close.

First is the CO2 radiative forcing effect. There are a large variety of ways to parametrize the atmospheric layers, even with our apparently pretty good knowledge of the radiative physics. Chapter 10 of IPCC AR4 WG1 goes into the projection issues in some detail, with section 10.2 in particular looking at radiative forcings. Table 10.2 shows the forcings for doubled CO2 from a variety of different models: there is some residual uncertainty but the average is 3.80 W/m^2 forcing, with standard deviation 0.33 W/m^2.

Now a nearly 10% standard deviation in a key number is pretty good for science, but it’s pretty abysmal for engineering – perhaps the first clue that we’re not talking about engineering here!

Second is the temperature response to forcing. Assuming the forcing is small, the response should be linear in the perturbation; the question is what is the ratio. James Annan gives the mean Stefan-Boltzmann response, which would be fine if the Earth were uniformly at the effective temperature and the total greenhouse effect was small. But it’s not (though not bad as a very rough approximation – Annan perhaps thought an engineering account would be happy with 50% error-bars…). You have to take into account the range of present temperatures and atmospheric layers to get an accurate response temperature; this is roughly Moeller’s calculation of 1966 referenced at Spencer Weart’s site:

Möller, Fritz (1963). “On the Influence of Changes in the CO2 Concentration in Air on the Radiation Balance of the Earth’s Surface and on the Climate.” J. Geophysical Research 68: 3877-86. http://www.aip.org/history/climate/Radmath.htm

Moeller’s number for the bare response to doubling CO2 was 1.5 K. This is under the assumption of no water-vapor response (no increased evaporation and latent-heat effect either). The error-bars on that should be at least the 10% standard deviation in the pure radiative number (so 1.35 K wouldn’t be unlikely).

Adding in the water-vapor response is where you actually have to go to the detailed climate models. Contrary to Steve M’s claim above, the climate models these days don’t “assume constant relative humidity”, they calculate physical processes at sea surface/air boundaries and look at the resulting water vapor, temperature, and other numbers for the different atmospheric layers in the grids.

With his most solemn Voice of God, the Auditor answers:

I’ve asked proponents for a few years now to provide an engineering quality derivation showing how doubled CO2 leads to a big problem. Thus far, I haven’t been able to get anyone to give me such a reference. Gerry North, a prominent climate scientist, has made fun of me for asking such a question, but maybe you’d have better luck with him than me. Unlike many readers, I do not presume that such a derivation is impossible or even that it doesn’t exist. If you can locate one, please bring it to my attention.

Presuming that something:

exists,

is necessary, and

has not been located after many years of search

looks a lot like looking for the Round Tuit.

I have yet to locate an engineering level report showing that the "correctness" of the "CO2 global warming hypothesis" might not depend on an engineering study for a chemical plant or semiconductor plant or space station.

An engineering report is not issued to everyone on earth. It is issued to a specific audience with specific interests and specific sophistication on specific topics. The closest thing possible, in short, may well be something the IPCC WG I report and the literature to which it refers.

The alternative is to address the document to people with a particular level of sophistication, for instance, people who are ready to take their prelims in a serious meteorology/oceanography program. Such a document might well be very different in character from WG I, but it would follow on at least three or four semesters of slogging through textbooks.

Is an engineering report of the sort McIntyre envisions accessible to a general population, say understandable at the level of a high school education and yet compelling at a PhD level? Harder still, to such a population which includes many people inclined to disbelieve every word? It is hard for me to believe that such a document exists in any field. If it does, I would be eager to see it.

That all said, I appreciate the frustration that many are expressing, having come into the field from an undergrad engineering degree. The pedagogy in engineering is much clearer, and the problems are much cleaner, than in the climate sciences. It’s not surprising: a smaller student population gets a weaker pedagogical tradition.