Economics is wrong, therefore (by analogy) physics is wrong

Since this mentions economics, it lets me talk about it in a way that is germane to this blog.

Let me get this out of the way: anyone who thinks global warming doesn't exist, global warming won't warm the planet by a few to several degrees over the next hundred years, and/or global warming won't be disastrous for Earth is basically a terminal fool. Whatever the reason -- Dunning-Kruger, bias (money or tribal), idiocy, or terminal contrarianism -- there is one; you just have to find it. So let's go!

Megan McArdle makes this seriously flawed analogy:

Economists can't run experiments in which they change one variable at a time. Indeed, they don't even know what all the variables are. ... Because climate scientists, like the macroeconomists, can’t run experiments where they test one variable at a time, predictions of feedback effects involve a lot of theory and guesswork.

McArdle has an English degree and an MBA; if this isn't Dunning-Kruger, I don't know what is. 

False equivalence 1:

In one case, the fundamental theoretical principles of the micro theory are known and tested to multiple decimal places; and in the other there are completely false assumptions of rational utility maximizing behavior and Calvo pricing.

Knowing the micro theory allows you to theoretically isolate variables to study the macro theory. Therefore there is no requirement about experiments isolating one variable at a time. If there was, astronomy would be in some pretty serious trouble because it can't isolate any variables.

In my personal opinion, this claim rises to the level of requiring a retraction of the article. It's like claiming 2 + 2 = 5; it's completely wrong.

False equivalence 2:

In physics (and the natural sciences in general), there is a principle that we call "naturalness" where we use scales to understand the system. The choices for your dimensionless coefficients (numbers without units, having been removed by identifying scales) in your theory are restricted to the set of 0, 1, or infinity. You can think of infinity as the "dual" of zero that tells you that one-over your dimensionless number is zero. Choosing some other number -- like a thousand or a ten-thousandth -- requires an explanation. That's at the heart of the hierarchy problem as well as the strong CP problem in physics (they're sometimes called fine-tuning problems). A few days ago I responded to a commenter using exactly this naturalness principle with respect to global warming:

The Earth converts a few high energy photons into many low energy ones (entropy production). Due to that conversion, the existence of CO2 absorption in the infrared, and the random emission direction of the absorbed photon (quantum mechanics), the final result is a higher temperature on Earth with CO2 than without. Without any CO2, the Earth would be about 40 K colder (the temperature of the Earth without atmosphere). Obviously changing CO2 levels by upwards of 20% should -- assuming the coefficient is natural -- produce approximately 20% of this warming effect. That would be about 8 K -- or at least its equivalent in thermal power divvied up among the water and land, which is the the more uncertain bit. Even a silly allocation where 75% of the power goes into the water and doesn't raise its temperature at all leaves you with 2K. Both the 8K and the 2K are perfectly in line with the range of climate forecasts. 

Any of the arguments against global warming have to claim an unnatural coefficient for the impact of CO2 (i.e. a 20% change in CO2 leads to x << 20% of temperature change), which is why they'd tend to be dismissed out of hand -- at least by physicists. It's just not consistent with what we know about CO2. And if they claim an unnatural coefficient for CO2, then they have to explain why the Earth is 300K and not 250K.

This naturalness principle allows you estimate the effects of perturbations to variables without necessarily controlling the other ones.

In traditional economics [1] there is no such principle because coefficients could have been chosen by human decisions, bureaucratic inertia, or through some strange socio-political process (think 2% inflation). You can't make estimates of theoretical effects in economics because you can't isolate scales (almost everything is dimensionless except time) and use naturalness arguments.

That's basically it. Unless it contains an argument against the naturalness of the impact of CO2 absorption in the infrared, anyone's skeptical position can be dismissed out of hand. That goes for "lukewarmists" as well. Global warming predictions make sense given the back of the envelope calculation I did above, and it would take something comparable to convince any scientist otherwise.

McArdle's argument is that because economics has no scales, naturalness, or fundamental theory, physics (by analogy) has no scales, naturalness, or fundamental theory. Using that argument you could say that because economics is not empirically successful, physics (by analogy) is not empirically successful. I hope the sheer idiocy of making such a stupid argument is clear.

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Update

Someone linked to this post in comments on a pro-free market blog, which prompted a response (quoting me above and adding emphasis) that gives an excellent counterexample of the proper use of the null hypothesis:

Fail.

Obviously changing CO2 levels by upwards of 20% should — assuming the coefficient is natural — produce approximately 20% of this warming effect. 

The assumption is invalid.

If the assumption is invalid, there must be a reason. That is the entire point of the strong CP problem (the assumption of a natural coefficient for the CP violating term in the QCD Lagrangian is orders of magnitude off, for which the axion is offered to explain). And if the assumption is prima facie invalid, its negation should be a valid starting point -- i.e. assume the coefficient is unnatural. Sounds rational! And if the coefficient is unnatural, why is the earth not a ball of ice?

This commenter would look at the hierarchy problem and say: What's the big deal?

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Footnotes:

[1] In information equilibrium, naturalness should hold. However for non-ideal information transfer all bets are off.