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Having been introduced to Ricochet on the wonderful National Review cruise, I would like to make my inaugural contribution about ‘climate science’. To begin with, let me say that I am a physicist and, though I have looked into the question of global warming a little bit in the past, I am certainly no ‘climate scientist’. In fact, this term is in any case misleading, I think, because the climate is a very diverse subject and it is quite impossible to be an ‘expert’ on every aspect of it. An expert on tree rings is not likely to be an expert on the physics of cloud formation as well. Needless to say, I am neither.
It is in fact with some reluctance that I write about this topic, because it is a political distraction. The scientific foundation is obviously far too uncertain to be a basis for taking any drastic action with deleterious economic consequences. In fact, ‘global warming’ seems to have paused, but even if this were not the case it is not clear that a small increase in average temperatures would not overall be more beneficial than harmful. And even if it had not stalled and it were more harmful than beneficial, then drastic action might well still be inadvisable because deteriorating economic conditions would make it more difficult to deal with any harmful effects.
A healthy dose of skepticism is apposite. The global warming scare clearly suits the Left, because they embrace world-wide action and international organizations. Moreover, it distracts from the avalanche of bad news they are facing currently. It is therefore probably unwise to engage in arguments with them about it at all. They are too comfortable in their beliefs to be open to debate.
At the same time, I sometimes hear arguments like: The amount of carbon dioxide in the atmosphere is a tiny fraction, so that cannot possibly make a difference. This is wrong, and it is therefore perhaps useful to explain why.
In early 2009, I became interested in models for global warming after reading about the hockey stick controversy. It seemed to me that it was convincingly shown by McIntyre and McKitrick that this work was erroneous, so it irritated me that Nature never retracted the hockey stick paper. The other main pillar of global warming theory seemed to be computer models. The assumptions that go into such models intrigued me. Unfortunately, the actual computer algorithms are difficult to get hold of, so I decided to try something simple myself. At this point it is useful to explain the role of models in science in general.
From grand scientific theories like the theory of relativity, quantum mechanics and evolution theory one may get the impression that scientific models are precise and detailed. This is a misunderstanding. Most models of physical systems are, on the contrary, quite deliberately caricatures. The art of constructing a model is to isolate the relevant features of a system for explaining a particular phenomenon, while ignoring various other characteristics that are not significant for that phenomenon. For example, in order to understand why iron can be magnetized (this is called ferromagnetism), one does not describe the state of all iron atoms in an iron bar in detail, but singles out the interaction (forces) between single electrons in each atom and, moreover, simplifies this interaction to a manageable form.
This may be somewhat abstract, so here is another, more easily understood example. Consider an object falling from a height. According to Newton’s laws, its speed increases linearly in time, because it moves in an essentially constant gravitational field. (In fact, this is already an idealization, because the field strength decreases with height.) Moreover, as Galileo showed, the speed is independent of the mass (weight) of the object.
Actually, this a bad model. We all know that a feather falls more slowly than a lead ball. One needs to take air resistance into account. Einstein already said: a model should be as simple as possible, but no simpler. An approximate way to take air friction into account is to assume that the friction force is proportional (but opposite) to the velocity. With this assumption, one finds that the speed approaches a constant value. This is the principle of a parachute: if the friction is large enough, the final velocity remains small enough so that one can survive the fall.
Notice that this simple assumption about the friction force is a caricature: the actual friction force will depend on the precise shape and movement of the object, and its dependence on the velocity is also, in general, more complicated. Nevertheless, this model is quite useful in many circumstances and has the advantage of simplicity: there are few adjustable parameters. The more parameters, the less predictive power a model has.
Coming back to global warming, I decided to construct as simple a model as possible describing the effect of carbon dioxide on the global atmospheric temperature. Is it even reasonable to assume that a trace gas can have a significant effect on the average temperature? In fact, this in not unreasonable (and of course, it is already a very old idea). It is essentially due to resonance.
When a column of soldiers crosses a bridge, they are told not to march in step, because their regular marching step could be in resonance with a particular characteristic frequency of the bridge, causing it to swing wildly. Similarly, molecules of particular gases have (bands of) special characteristic frequencies. If they are radiated with (infrared) light of such a frequency they start vibrating, thus absorbing energy from the radiation.
The Earth’s surface radiates approximately as a black body, i.e. its radiation varies in strength (intensity) with the frequency, with a maximum in the infrared. Some of this radiation is in resonance with water molecules, which are abundant enough so that the absorption is mostly saturated for those frequencies. However, two of the three absorption bands of carbon dioxide lie outside those of water. In particular, the main band is not entirely saturated at the edges. This means that increasing the amount of carbon dioxide in the atmosphere will increase the absorption in the edge of the band.
One can show that this follows a square-root law. Adjusting the constant in front of the square root, one can get reasonable agreement with the observed global warming from 1880 until 2008. (There are, of course, large fluctuations on top.) At the time, I tentatively concluded that this might be a sensible model, dismissing the reported recent leveling-off as a short-term fluctuation. However, it is essential for scientists to be honest in assessing their theories. It seems that this period of stable temperatures has now lasted for some 15 years and looks less and less like a short-term effect. The model is therefore inadequate. Some relevant variable has been omitted.
At this stage, it is perhaps appropriate to make a remark about these temperature measurements. At first sight it might seem like a straightforward exercise to measure temperature. Thermometers are certainly very accurate, but they only measure a local temperature. To obtain the average temperature of the Earth’s surface, once has to perform an average — and it is far from clear how this should be done. Obviously, the thermometers are not distributed evenly over the Earth’s surface, so one has to give some a higher weight than others. This makes the highest-weight thermometers most significant and faulty operation or placement of these will have proportionately greater effect. Notice that these are likely to be the ones in the most inhospitable places and therefore more susceptible to faults.
The distribution of carbon dioxide in the atmosphere is in fact very uniform so the effect should be felt everywhere (though perhaps not to equal extent). As long as the distribution of thermometers is unchanged, one might hope that the precise method of averaging is not important provided that the temperature increase is significant and observed in most places. By the way, the term ‘global warming’ is a sensible name for this supposed phenomenon. ‘Climate change’ is an obfuscation because the climate changes due to other effects. Indeed, these are also still poorly understood, but may be supposed to happen on longer time-scales (although this is far from certain).
Coming back to the model, there are obviously many possible causes for the halting temperature increase: for example increased cloud formation, increased vegetation, volcanic activity, or solar activity. Some of these are back-reactions similar to the friction in the example above and could conceivably lead to a leveling-off. Incorporating them in the model is not easy, however. Perhaps some of these are incorporated in the complicated ‘general circulation models’ used, but these did not seem to predict the leveling-off of the global temperature, so this is hardly convincing.
A few more remarks about the science. Some of the carbon dioxide is absorbed in the oceans. Because the partial pressure of CO2 is low, the absorption is not large and because carbonic acid is a weak acid, it seems to me that acidification of the oceans due to this effect is insignificant.
Another consequence of global warming would be rising sea levels. As in the case of measurements of the global temperature, measuring the average sea level is not straightforward: it is a very small effect superimposed on large fluctuations. Nevertheless, measurements seem to show that there is a systematic effect amounting to roughly 2 millimeters per year. This is hardly something to worry about in the foreseeable future. Moreover, a rough calculation shows that it agrees with the thermal expansion resulting from the observed temperature increase. With the global temperature seemingly having stabilized, this should also level off, but I am not au fait with recent measurements.
I apologize for the length of this piece but I hope it serves the purpose of illustrating how a skeptical scientist might think about this topic. By the way, contrary to how it is often portrayed, I am by no means the only skeptical scientist, and in any case, scientific facts are not established by majority vote. Indeed, it is often dissenters who show the way forward.