Environment: April 2009 Archives


April 20, 2009

Look if John Boehner wants to believe that global warming isn't happening or isn't bad or whatever, then fine. But can we at least be spared this kind of stupidity:
STEPHANOPOULOS: So what is the responsible way? That's my question. What is the Republican plan to deal with carbon emissions, which every major scientific organization has said is contributing to climate change?

BOEHNER: George, the idea that carbon dioxide is a carcinogen that is harmful to our environment is almost comical. Every time we exhale, we exhale carbon dioxide. Every cow in the world, you know, when they do what they do, you've got more carbon dioxide. And so I think it's clear...

OK, so this is, as Wolfgang Pauli is supposed to have said "not even wrong". First, nobody is claiming that CO2 is a carcinogen. The reason people want to reduce CO2 emissions isn't that they give you cancer, it's that CO2 causes global warming. So, the fact that you exhale it hardly leads to the conclusion that it's somehow a great idea to radically increase the CO2 content of the atmosphere.

Even if the reason to restrict CO2 was that it was bad for humans instead of the environment (like, say mercury) this wouldn't follow. Have you noticed that you're inhaling CO2? It's a waste product from aerobic respiration (look up the Krebs Cycle). Boehner's argument is like suggesting that feces isn't bad for you because you emit it regularly, as do cows, etc., but I'm assuming he'd like to minimize his feces consumption.

Interestingly, while CO2 is a waste product, it's not actually toxic. You wouldn't want to breathe an all CO2 atmosphere, but CO2 is what stimulates the breathing reflex. Oxygen, on the other hand, is fairly toxic once you get too far above the normal partial pressures in the atmosphere.


April 11, 2009

Julian Sanchez's post about the difficulty of evaluating technical arguments has been circulating fairly widely. In the middle is a somewhat strained analogy to cryptography:
Sometimes, of course, the arguments are such that the specialists can develop and summarize them to the point that an intelligent layman can evaluate them. But often--and I feel pretty sure here--that's just not the case. Give me a topic I know fairly intimately, and I can often make a convincing case for absolute horseshit. Convincing, at any rate, to an ordinary educated person with only passing acquaintance with the topic. A specialist would surely see through it, but in an argument between us, the lay observer wouldn't necessarily be able to tell which of us really had the better case on the basis of the arguments alone--at least not without putting in the time to become something of a specialist himself. Actually, I have a possible advantage here as a peddler of horseshit: I need only worry about what sounds plausible. If my opponent is trying to explain what's true, he may be constrained to introduce concepts that take a while to explain and are hard to follow, trying the patience (and perhaps wounding the ego) of the audience.

Come to think of it, there's a certain class of rhetoric I'm going to call the "one way hash" argument. Most modern cryptographic systems in wide use are based on a certain mathematical asymmetry: You can multiply a couple of large prime numbers much (much, much, much, much) more quickly than you can factor the product back into primes. A one-way hash is a kind of "fingerprint" for messages based on the same mathematical idea: It's really easy to run the algorithm in one direction, but much harder and more time consuming to undo. Certain bad arguments work the same way--skim online debates between biologists and earnest ID afficionados armed with talking points if you want a few examples: The talking point on one side is just complex enough that it's both intelligible--even somewhat intuitive--to the layman and sounds as though it might qualify as some kind of insight. (If it seems too obvious, perhaps paradoxically, we'll tend to assume everyone on the other side thought of it themselves and had some good reason to reject it.) The rebuttal, by contrast, may require explaining a whole series of preliminary concepts before it's really possible to explain why the talking point is wrong. So the setup is "snappy, intuitively appealing argument without obvious problems" vs. "rebuttal I probably don't have time to read, let alone analyze closely."

Unfortunately, Sanchez has the cryptography pretty much wrong. He's confused two totally separate cryptographic concepts: public key cryptography, and one-way hashes. Some PKC (but not all) involves multiplying large prime numbers. Hash functions (with the exception of VSH, which is impractically slow and not in wide use), don't involve prime numbers at all. Neither does symmetric encryption, which is what you actually use to encrypt data (PKC is used primarily for key exchange and authentication/signature). Now, it's true that prime multiplication is indeed a one-way function (or at least we hope it is) and hash functions are intended to be as well, but other than that, there's not much of a connection.1 That said, however, I've seen this post referenced several places, and with the exception of Paul Hoffman, who pointed it out to me, few seem to have noticed, that, well, it's horseshit. I suppose this is an argument in favor of Sanchez's thesis.

1.Hash functions are actually one-way in an important sense that prime number multiplication is not: any given integer only has one unique factorization, whereas there are many messages that hash to a single value, so it's always possible with enough computational effort to reconstruct the original primes. However, given a hash value and no other information, it's not possible to determine which of the possible input messages was fed in.