I did not want to write a technical post on global warming. There is plenty of information on this issue available on the Internet, and I thought that everyone with an interest in the subject would just go ahead and read. Still, after it had become clear that my discussion of this issue with Nathan in non-technical terms hit the wall, and I was accused in dismissing offhandedly the entire “scientific field of climatology”, I gave up and started researching this post. I did not intend to become an expert climatologist, but I did go as far as to read a few original research papers in peer-reviewed climatology journals such as Journal of Climate, Journal of Geophysical Research and such. I am obviously still not qualified to judge who is right in the climate change debate, the majority of the alarmist, or the minority of the skeptics, but this much I feel qualified to say: despite the vocal claims to the opposite, the science of the climate change is very far away from being fully understood and settled. Frankly speaking, I was appalled by an extremely low, by standards of my own area of science, level of argumentation and analysis of the data presented in the papers I have read. But I am running a little bit ahead of myself here, so let’s go back to basic.
The physical foundation of the global warming theory is so called “greenhouse effect”. To understand this effect one needs to realize that the solar radiation falling on the Earth comes in many different varieties: radio waves, infrared radiation, visible and ultraviolet light. All of this is essentially just electromagnetic waves, which differ from each other by their wavelengths: longest for radio waves and shortest for ultraviolet light. Waves with different wavelengths interact differently with atmosphere, oceans, ground, living organisms, etc. It is crucially important that the atmosphere is transparent to the visible light (this is why we can see it), but is not transparent to the infrared radiation. The reason for the latter is the presence in the atmosphere molecules, mainly water vapor, and to a lesser extent carbon dioxide and others, which are oblivious to other forms of electromagnetic radiation, but strongly absorb infrared waves. Therefore, the visible light travels almost unobstructed through the atmosphere, where it is either reflected back or absorbed. When electromagnetic radiation is absorbed, it is necessarily re-emitted, but in the form of infrared light, which cannot get through the atmosphere. Thus, a significant portion of the energy of light radiation remains trapped in the Earth-atmosphere system. The atmosphere still emits certain amount of infrared radiation as determined by its temperature to the outer space. This temperature is defined by the equilibrium between amount of absorbed sunlight and the emitted radiation (the Earth warms up or cools down until it emits as much energy as absorbs).
The greenhouse effect is a well-understood physical phenomenon, which plays positive and essential role for life on this planet. Without it, the temperature here would have been too low for any life to be possible. However, while being the physical foundation of the global warming theory (GWT), the greenhouse effect by itself is not part of it.
GWT can be presented in the form of three postulates
- The average temperature on the Earth increases
- This increase is due to extra amount of carbon dioxide released to the atmosphere because of human industrial activity. This extra CO2 results in more solar radiation being absorbed, and, therefore, warms up the Earth to balance out this increased absorption with more emission.
- Increase in temperature will result in drastic climate changes with catastrophic consequences for Earth’s ecosystem, including human population.
Let me begin with the first of these statements, which is the least controversial, and this is what most people have in mind when they talk about the overwhelming empirical evidences of global warming. I will not discuss in too many details the actual observational base of this statement, even though there is still some controversy between temperature measured by the land-based stations, and data obtained from satellites (the latter show much smaller warming). Instead, I want to focus on meaning of the concept of average temperature.
The concept of “averages” is one of the most widely used and most misunderstood ideas in natural and social sciences. One uses this concept to replace a complex set of apparently random data with a single number, which can be done with a clearly defined mathematical procedure (just add all your data together and divide by the number of entries in your data-set). What is not that obvious is the actual meaning and usability of the derived number. An example of a meaningless average is “the average temperature of patients in a hospital”. On the other hand, the average number of votes projected for a candidate for political office is an example of meaningful average. What is the difference between these examples? In the later example, winning or losing an election is determined by the cumulative effect of many voters making their choices, while in the former case there is no quantity whose value would depend on the cumulative effect of individual patient’s temperatures. I suspect that the average temperature in the context of global warming is akin to the average temperature in the hospital because none of the essential climate related quantities is determined by cumulative effects of daily, monthly or annually changing temperatures.
The climate scientists do understand this, and it seems to me that average temperature data are constructed mostly for external consumption: politicians, journalists, and political activists of all persuasions. For internal discussions, other measures of global warming are used. One of the most meaningful metrics is global heat content of the oceans. I was surprised, however, to discover that this indicator shows a lot of volatility even though one would expect the changes of the total thermal energy of the oceans to be very slow reacting only to cumulative effects. Still, these numbers are much more indicative then average temperatures, and they show that starting from about 2000 the heat content of the ocean is flat or even decreases indicating absence of warming. This point is of course being debated on both sides up to now, but the very existence of this debate shows that even with the first postulate of GWT, the situation is not as settled, as its proponents would like us to believe.
Another popular indicator used as a proof of the first postulate of GWT employs the mass of ice in Antarctic. This indicator, however, is not as clear-cut as the ocean heat content because there exist too many different phenomena that could influence melting of ice in Antarctic, such as direct sun light, ozone layer, cosmic rays and others. But even the melting phenomenon itself is not that straightforward: while the land ice in Antarctic does melt, the amount of sea ice shows unprecedented growth. It is interesting to note that the melting of Antarctic ice occurs faster than predicted by the climate models. While this fact is taken by the advocates of global warming as its even “stronger than expected” confirmation, it is really not. This fact simply shows that climate models are not reliable, their predictions are not trustworthy, and that no one really understand why the Antarctic melts.
The situation with the second postulate of the global warming theory is even worse. No one argues that industrial activity increased the amount of carbon dioxide in the atmosphere. At the same time no one also disputes the fact that the direct contribution of CO2 into greenhouse effect is very small - about one degree of centigrade for doubling of the amount of CO2, and we are still far away from this threshold. However, this small effect can be amplified through so-called feedback mechanisms. This means that rise in temperature due to small increase of CO2, which would have been otherwise negligible, stimulate additional processes, which affect the climate in a much stronger way by either enhancing the warming effect (positive feedback) or reducing it (negative feedback). The cornerstone of the global warming science is the assumption that main feedback mechanism is water vapor feedback, which is strongly positive, and, therefore, even small changes in CO2 concentration results in exponentially increasing temperature. The physical origin of this feedback lies in a simple fact that warmer air can contain more water vapor, which in its turn, absorbs more sunlight producing more warming. The problem with this picture is that this is not the only possible feedback mechanism.
Everybody agrees that clouds whose formation is affected by increased water vapor content of the atmosphere, also provide an important feedback mechanism. What scientists cannot agree upon is the type of this feedback: on one hand, clouds reflect more radiation back to space (negative feedback), but on the other hand, they trap more radiation emitted by Earth (positive feedback). Richard Lindzen of MIT argues that the cloud feedback is strongly negative so that it cancels the positive water feedback. Dessler of A&M University and others find the cloud feedback to be either positive or small negative. The uncertainty in the cloud feedback has not yet been resolved as admitted in 2010 Science article by Dessler, which makes it very difficult to know the overall feedback with any certainty.
This overall feedback determines so-called climate sensitivity, which is the crucial parameter for the GWT. If this parameter is large and positive, then the climate is indeed very sensitive to even small changes of CO2 and the humanity is in danger, but if this parameter is small or negative, we still have some hope to survive without wrecking our economy.
Another approach to determining the total feedback is based on statistical analysis of empirical data such as surface temperature and radiation imbalance (difference between incoming and outgoing radiations) in the upper atmosphere. I already mentioned that average temperature does not really measure much, and even if it does, whatever it measures depends on a number of quite arbitrary decisions, and is, therefore, highly uncertain. Given these uncertainties of the input data and a number of arbitrary assumptions unavoidable in this type of analysis, it is not surprising that different researchers come up with opposite conclusions. Therefore, I personally think than none of the results obtained with this approach can be taken seriously and that level of certainty of our knowledge of climate sensitivity implied by the Intergovernmental Panel and the media is strongly overblown.
To conclude the discussion of the 2nd postulate of GWT I want to make another point. Even if the value for the climate sensitivity provided by the Intergovernmental Panel is close to reality, the estimates of the future based on this number are seriously flawed for another reason. The whole concept of feedbacks and climate sensitivity assumes that these parameters themselves remain constant over time. This type of assumption is called linear approximation. This approximation is only valid in the close vicinity of equilibrium. When a system moves farther away from equilibrium, and this is exactly what is being implied by GWT, the linear approximation unavoidably breaks down. In order to know how far from equilibrium a system can go before this happens, we must have models going beyond the linear approximation. I am yet to find papers seriously discussing this issue, and without such a discussion, conclusions based on linear models do not worth much.
Finally, I will say just a few words about the third postulate of the GWT. It is not necessary, though, because analysis of the second postulate already has shown that Freeman Dyson was completely correct saying that the climate science is in a crappy shape. Still, I want to add a few words about long-term predictions of the climate models. Climate is a complicated nonlinear system, and if we know anything about generic nonlinear systems, it is that their dynamics is extremely sensitive to initial conditions and values of the parameters. This means that even a smallest change of one of the parameter can result in completely different predictions, and I do not mean different numbers, I mean different equilibrium states. This conclusion is a rigorous mathematical result in the theory of nonlinear dynamic systems, of which climate is one of the examples. (For those familiar with nonlinear dynamics: I do realize that situation is more complex: there are regions of parameters and initial conditions with stable behavior, as well as those with unstable; there are different types of equilibrium,or better steady states, which can be reached from different initial conditions, but these too much technicalities for this post intended for general public. I am afraid I have already bored everyone to death.) For instance, modern computer climate models include only interaction between atmosphere and oceans, but do not include effects of biosphere (trees, plants, CO2 eating plankton in the oceans, etc.). Even though, these effects appear small, over a long time interval due to the instability of the nonlinear dynamics, they can completely change the fate of the climate. How long is this long time interval? May be some climate scientists know, but they do not share this knowledge with broader public. These arguments do not mean to say that no catastrophic events can ever happen; they mean that these events are not predictable and not controllable.
To conclude, I believe I made a good point showing that the climate science does not yet have a well-established paradigm, and that its unresolved difficulties are of fundamental nature, which has to be resolved before any real paradigm can be formulated. Accordingly, I believe that it is quite irresponsible to force any political and economical actions with global consequences based on this kind of theory.
Lev, many thanks for the clear and cogent critique of climate science. If I ever need to learn about physics, I'm signing up for your class! This holds a lot more water as far as I'm concerned than simply questioning the motives of the "alarmists."
ReplyDeleteObviously, I don't have the expertise to present a rebuttal on your level, but I did have some questions as I read and reread your post. I'll serve then up and you can tell me what you think.
First, on the issue of averages, and more broadly, whether a warming of the global climate is actually taking place. You say that global average temperature is a meaningless statistic because no other values are determined by it. But perhaps the average can be used in a different way as a longitudinal indicator--a value that shows a dynamic of change over time. Assuming of course that the methodology for determining the average temperature is consistent from one year to the next, I would think that the picture of change that emerged would be a significant indicator.
You seem to be saying, however, that the dynamic illustrated by a year to year tracking of the global average temperature is essentially meaningless noise with no bearing on any other processes. But it seems to me that this pattern is reinforced by a whole series of other indicators. The average global temperatures in recent years show a clear warming trend, and sure enough we also find in the same period the shrinking polar ice caps, the rapidly melting Greenland ice sheet, disappearing glaciers from Mt Blanc to Mount Kilimanjaro, mushy permafrost, earlier onset of spring, changes in migrations routes, disruptions of established weather patterns, etc. etc. In short, there seems to be an overwhelming preponderance of evidence that confirms the trend of global warming shown by the average global temperature. Is something wrong with this scenario?
Incidentally, climate change deniers are by no means averse to using global average temperature when they feel it's to their advantage. I've occasionally heard the claim that global warming has stopped since 1998. Actually this is totally disingenuous. It turns out that 1998 saw a record peak in average temperature that has not yet been matched. If you take 1998 as a starting point, there would appear to be a downward trend. But if you take an earlier year, say 1980, as a starting point, it's clear that the warming trend is continuing and that 1998 is actually the anomaly.
to be continued...
The dependence of the apparent trend on the choice of the starting point is one of the reasons why I call average temperature a meaningless indicator. As far as "trends" in general are concerned, they all depend on the time period used to compute averages (I mentioned it in my post). Dynamics of temperature can be characterized by many different time scales, not all of which are known. By averaging over short (3-5 years) periods we eliminate fluctuations on this time scale, but we do not know if what we see in the remaining dynamics is indeed a "trend" or just another longer scale fluctuation. For instance, there are processes, called fractals, which have the same behavior on any scale. This means that by averaging out short term fluctuations you are left with fluctuations of exactly the same form but stretched in time over longer period.
ReplyDeleteSome of other indicators that you mentioned might make more sense, but I would not include in their numbers bird's migration patterns and unusual weather patterns because I can perceive them only as secondary indicators. The only mechanism, by which temperature 3 years ago can affect weather pattern today, is the heat of oceans. Thus, I would have stick with this quantity as the primary indicator, and would analyse the other phenomena as effects due to this cause.
Finally, there are no questions that in the "deniers" camp there as many disingenuous and scientifically illiterate people as in "alarmist" camp, but we are not talking about them, are we?
Thanks for the response to my first query. Here's a second one, which I wrote before I saw your response.
ReplyDeleteTurning to your second postulate on the role of carbon dioxide, I have a few questions here as well. It seems to me that you have succeeded in casting a haze of uncertainty over the premise of man-made global warning, but not necessarily vanquishing it. You provide a very clear explanation of the mechanism of the greenhouse effect and explain that the role of carbon dioxide depends of the effect of feedback mechanisms which can either be positive or negative--reinforcing or counteracting the overall trend. So far so good. The question is which type of feedback is stronger. I gather from your post that the jury is still out and that some scientists such as Lindzen at MIT have suggested that negative feedback will offset whatever warming trend might arise from increased CO2 in the atmosphere. I suspect that many scientists, including a number of Lindzen's colleagues at MIT would not necessarily agree. But actually my question is in a different area. As you know, the earth has gone through a number of warming periods in the fairly recent geological past and that by using ice core samples and other indicators, it is possible to measure the composition of the atmosphere during these periods. The results, as I understand them, suggest that these warming periods in all cases correlate with a higher level of CO2 in the atmosphere. The authors of these studies, incidentally, are not necessarily claiming that CO2 caused these warming trends--the heightened CO2 often appears after the warming is under way. But they do suggest that it accelerates warming once the initial trigger has appeared. In other words it acted as a feedback mechanism. But there is no reason why CO2 would not have the capacity to trigger a significant warming trend on its own if a large amount were to be introduced into the atmosphere in a short period of time. Thus the relationship between CO2 and warming seems to be firmly established by the historical record. What's your take on this?
I appreciate very much your comments on the complexity of situations in which multiple variables are at work, as well as the point that minor variations in initial values can have an enormous effect on outcomes. This is actually very much the way historians like to think, and it is why historians are generally strongly averse to predictions of future events. In general, I'm much less persuaded by climate scientists models of future trends than I am by their ability to explain what has already happened in the recent past and continues up to the present. But let's just say that you're right and that there is considerably more doubt about global warming than the 'alarmists' would have us believe. Nonetheless, you yourself sketch out the mechanism through which global warming could be taking place. You have called the aspects model into question, but not refuted it completely. So the question is how should we behave under these circumstances. Should be simply go on with our lives as if nothing was happening in the hope that the alarmist scenarios prove to be false? Or do we take prudent preventative measures based on the reasonable probability that we are at risk? The situation reminds me of the dilemma of a smoker, who knows that there is an increased likelihood of getting cancer if he continues smoking, but also knows that there will always be a number of people who continue to smoke until a ripe old age, without ever suffering any ill effects. Do you take your chances in the hope that you'll be one of the lucky ones, or do you take the necessary steps to reduce your risk, even if can't know for certain whether you would have fallen victim? It seems to me that perhaps prevention would be the wiser course.
In a response to your question about past warming periods, I would like to point out to two things. First, CO2 was not the cause, but rather an effect of the original warming as you said, and this is very important point. It is important because the next step in this argument is that CO2 accelerated warming after it had appeared is not necessarily true. I did not look into details, but all those warming periods were followed by cooling periods. This suggests several alternatives: (i) dynamics of temperature had nothing to do with CO2 whatsoever (once original warming mechanism disappeared, the system returned back to cooler temperature, regardless of CO2 presence), (ii) the overall feedback triggered by initial increase of temperature was negative (by the way, it is a common misunderstanding that the feedbacks react to CO2; in reality they react to temperature changes); (iii) the feedback was positive but as the system moved away from the initial equilibrium, the nonlinearity, which is neglected in the feedback picture, prevented the significant rise of temperature and shifted a system to a new, cooler equilibrium. My guts tell me that (i) or (ii) are more likely, but I cannot exclude (iii) as well.
ReplyDeleteNow, about your smoking analogy. I think it is wrong on many levels, but one of them is most significant. In the case of global warming you are making decisions not just about yourself. These decisions will affect billions of people now and even more in the future. Wouldn't you agree that in the case of decisions of so great consequences, the level of certainty in premises, on which decisions are made, must be much higher and not lower?
ReplyDeleteYou are asking, what to do? Well, first of all, do no harm. Then, come up with policies that would unleash people's creativity in developing new ways of producing energy. We have to move away from oil and coal one way or another, but it must occur naturally the same way we moved from manual labor to steam engines, and not by wrecking the entire civilization and its ability to make this transition. Should we develop new technology, based on solar and other renewables, develop electric or hydrogen fueled cars? Of course, but it should be driven by private interests, not by governmental decrees. Any way, it will only work, when someone finds a way to make profit out of it. Government, of course, has a role to play here by developing sound economics politicies and by helping markets, but not by obstracting them.
You will say, what if there is a catastrophe, how can we wait? Well, there will be catastrophes, and nothing anyone can do to prevent them. There is only one hope for the civilization: the unrestrained creativity of people and freedom for them to exercise it.