Normally I don’t read Charles Krauthammer. It would be like taking time out of my day to listen to the rantings of the guy who fills the bus with the smell of urine and his theories on black helicopters and communists massing at the border. But his latest missive mentioned science (The notion of “settled science” is in itself anti-scientific) so, against my better judgment, I bit.
What set Krauthammer off was this comment in the State of the Union Address: “The debate is settled. Climate change is a fact.” Apparently this tweaked a deeply buried, muddled, and rather moldy sense of scientific outrage in our intrepid journalist, prompting him to thunder
“There is nothing more anti-scientific than the very idea that science is settled.”
The rest of the article was spent ranting about mammograms, the nonagenarian Freeman Dyson, and the climate `pause’. I’ll get back to these later. But first, what about his claim? Is it scientific to talk about settled science?
I am currently teaching a course called “Science and Society” and one of the things I have stressed to my students is that science is not entirely rational, and in fact it cannot be (you cannot deduce your way to new knowledge). Science has cultural and historical influences; scientists must deal with biases and self-deception; and everything is contingent. In short science is a human endeavor. In principle this means science can never be settled. But no scientist ever uses the phrase “in principle” — science is far too practical to dwell in the philosophical world of might-have-been or could-become. Instead, science talks about in practice.
The phrase “in practice” is implemented in a specific way in science, known as setting a scale. Let me illustrate this with an example. Say that your wife hears scratching in the attic and sends you to look for a mouse. You return and announce that there is no mouse. But your wife is a philosopher (or a Krauthead) and asks how you know that you have seen no mouse. In principle you have no answer because you cannot guarantee that the things you did see were not very odd looking mice. Fortunately you are a scientist and have a response for her: the things you did see were not mice within a certain tolerance — none of them had ears, were furry, or scurried into corners. This tolerance is the scale that I am referring to (excuse me, “to which I refer”). When physicists use the notion of scale they often refer to a given length or energy, say one meter or 1000 joules.
What does this have to do with settled science? When scientists say they understand something they always mean within a certain range of scales. For example, light is one of mankind’s most perfectly understood phenomena: our theories for light work on scales ranging from 10-28 meters to 1021 meters — an incredible 49 orders of magnitude (I am being conservative here, the lower end can be pushed to the Grand Unification scale of about 10-32 meters, and the upper end can probably be pushed to the size of the universe, about 1026 meters). Another example is the conservation of energy, which is verified over similar length scales. The science of light and of conservation of energy are completely settled over these 49 orders of magnitude. Only a madman would waste time looking for violations of this settled science; instead scientists look to probe theories beyond the scales at which they are known to function. This is why the LHC particle accelerator; is so big and expensive. (An alternative is to look for emergent properties at known scales, but this is taking us too far afield).
Climate science is interesting because it happens over a large range of length scales. Dealing with all of these scales is what provides the intellectual challenge to the field, and spurs further research. The largest scales are set by jet streams and hurricanes and thus are a good fraction of the size of the Earth, about 107 meters. The smallest scales are set by chemical processes which occur at around 10-10 meters. One such chemical process is the depletion of ozone caused by the dissociation of CFC molecules by UV radiation and the subsequent combination of chlorine with ozone. Another process of concern is the absorption of thermal radiation by greenhouse gases.
The claim that climate change is occurring due to greenhouse gases rests on the properties of these gases, their interactions with light, and the conservation of energy. Recall that the science of these things is settled in a range of scales from 10-28 to 1021 meters, which is much larger than the scale of climate science. Our understanding of these phenomena is not going to change, or if they do, they will change at scales that are completely irrelevant to climate science. Thus the statement that CO2 causes global warning is entirely settled.
The questions that fill the time of professional climate scientists do not involve these fundamental laws of nature, rather they involve details that answer questions like “how rapidly will the earth heat?”, “how much will it heat?”, and “what effects will this have?” These are clearly important questions and the answers will likely change somewhat as the science improves, but the basic principles and effects are set in stone.
With that settled, I want to return to a valid point that Krauthammer made, namely too many people are claiming “climate change” as the cause for their favorite disasters. It is far too early to correlate climate change with weather (be careful to distinguish short term and volatile weather from long term climate patterns!). The cold snap this winter is a random (actually deterministically chaotic, but that is another story) event, just like the California drought, and the latest megastorms.
And finally, Freeman Dyson is a (very) old man and has lost it. It happens. One of last century’s greatest scientists was Linus Pauling, who regretably spent the last years of his life ranting about vitamin C. As for the “pause” — it is a fabrication of the deniers.