0. Background: Discussion at “Climate Etc.”
During the last weeks I have been following and participating in the discussion on Dr. Judith Curry’s blog Climate Etc. Most of the comments on that site present a skeptical view of climate science, but there are also commenters close to the main stream science and beyond. Dr. Curry is a climate scientist, whose description of her views can be interpreted as agreeing with the main stream science on all issues considered generally well known, but having less trust than most main stream scientists in results that are considered imprecisely known by others as well. As an example, she has given a significantly wider error range for the climate sensitivity.
Another characteristic of her site is that some guest postings have brought to discussion ideas that are clearly contrary to the mainstream views. Judith Curry has introduced some of them in a neutral fashion also in cases, which I would judge to be ill-conceived criticism of climate science using arguments, which approach fallacies of logic.
What is most striking to me in the discussions is perhaps the general difficulty of understanding, what the science is about, what it can provide and what not, or what can be required from science to make it valid and proper. Here I present briefly my views on some of these issues. The point of view is personal, but I expect it to agree largely with many active scientists, while some differences of opinion certainly exist.
1. Climate science and anthropogenic global warming (AGW)
The goal of climate science is to collect knowledge and understanding about processes influencing climate. The goal is not to prove or disprove AGW. Actually the question of proving or disproving AGW does not make logical sense. A more correct way of presenting the relationship between climate science and AGW is that climate science tries to find out, how human actions affect climate. There is no doubt that there is some influence, but determining its strength and details is one central problem of climate science. It is not the only one and from point of view of science itself, it is just a distraction.
The climate science does not study AGW forgetting other variability of the climate, but as one component of the comprehensive knowledge.
The requirement that AGW has to be proven is moot, as some influence certainly exists. Inverting the null hypothesis requiring that a strong AGW does not exist is slightly more logical, but not well defined. Therefore the whole concept of disproving some null hypothesis does not fit the problems related to AGW. The correct question is:
What do we know about the strength and other properties of AGW?
2. Empirical evidence and models
Climate is not the same as the weather at one point at one moment. It concerns statistical properties of weather as the weather varies in time. In most cases also wider areas are considered rather than a specific location. Typical climate parameters include average temperatures, extent of variation around the mean, severity and frequency of extreme temperatures as well as similar quantities related to precipitation, winds and other weather patterns. None of these quantities is directly observable; all require the use of some model. At its simplest the model may specify, how the measured temperatures are combined to get the average temperature at one measuring station, in other cases the empirical data can be used to calibrate a rather complicated model and the searched quantity is an outcome of the model. The second description applies, e.g., to satellite determination of the temperature of the lower atmosphere, and it applies to an estimation of the climate sensitivity. The view that there would be a fundamental difference between the simpler and more complex cases is unjustified. The uncertainties do vary and part of the variation is linked to the use of models, but there is no fundamental difference.
For every piece of knowledge the best evidence combines empirical data with model based analyzing methods. The models used are furthermore based on a combination of theoretical understanding and further empirical data that has been used to verify their validity and specify some of their parameters. How much the models used in the analysis of observations affect the reliability of the results, varies greatly from case to case. Thus no general conclusions can be presented on that. Particular problems arise from such uncertain model features that affect in a similar way the analysis of several sets of empirical data. The mutual agreement of results of the separate experiments may in such cases create false confidence, as one single uncertain parameter may cause an error in all of them. These problems have been discussed in the comments of my previous posting.
All assessment reports of IPCC have indicated that the most representative single parameter of AGW, the climate sensitivity remains highly uncertain (between 1.5 °C and 6°C with 90% certainty is one way of describing the present estimate; the climate sensitivity is the increase in the average surface temperature of the Earth surface that results from doubling the atmospheric CO2 concentration and keeping it at that level long enough for the temperature to reach its new value). Whether such quantitative limits can be considered objectively justifiable from scientific knowledge or whether the limits should rather be taken as a typical subjective assessment of individual scientists remains also unclear. Either way they the numbers appear to give a reasonable picture of the present thinking in the climate science community.
Even when all the above caveats are taken into account, it remains true, that results, whose analysis involves complex models are not necessarily any less accurate or reliable than more direct observations. Estimating their accuracy is often more difficult, but when that is done carefully such results should not be given any less value.
3. Physics and climate science
Atmospheric sciences including climate science are physical sciences. Their basis is in well-known laws of physics and in material properties measured accurately and reliably in laboratory experiments. Atmosphere and the larger Earth systems that include oceans, continents with their biosphere and glaciers are so complex that a full analysis starting from first principles is impossible. Much can, however, be learned from the basic physical knowledge without the need of building complex models.
The two most important fields of physics for basic understanding of the atmosphere are thermodynamics and the theories of the interaction of electromagnetic radiation (visible and infrared) with matter. Fluid dynamics is also essential, but its role in the analysis comes at a more detailed level of work. The basic structure of atmospheric models is based on fluid dynamics.
Thermodynamics tells how the temperature profile of the atmosphere is determined for most of the globe (in Polar Regions the profile is different). The result is that the temperature falls with altitude following the adiabatic lapse rate through the troposphere
The theory of interaction of the radiation with matter is based on theories of electromagnetism and quantum mechanics, or their combination Quantum Electrodynamics. On the molecular level the interactions are described by quantum mechanics. The results of the relevant quantum mechanical calculations have been combined with experimental data. On this basis the extensive Hitran data base is known to contain most of what needs to be known about the interactions. Beyond that point the simple picture of photon emission, absorption and scattering is sufficient for analyzing the radiative energy transfer in the atmosphere. There may be alternative approaches, but they do not give any additional value or change the results, they would probably make the analysis only more complicated.
The two physical theories described above form the sufficient basis for understanding the greenhouse effect and the radiative forcing of additional CO2 for an atmosphere where the only change in troposphere is a sudden addition of CO2. (The radiative forcing is defined as the reduction of outgoing radiative energy at the top of troposphere after such sudden change in CO2 concentration.) The calculation requires a description of the state of troposphere, but not any other knowledge about its behavior. The lack of need for any other knowledge makes the calculation of radiative forcing very reliable and rather accurate. The small inaccuracies are mainly due to the inaccuracies in the description of the atmosphere.
4. Scientific method and climate science
In discussion forums a common claim is that climate science is not done in accordance with proper scientific methods. These comments are based on erroneous interpretation of science, the scientific process, and the scientific methods. The critics set such requirements for science that are seldom applied in any field of science. The requirements originate often from Popper’s work. Popper presented an idealized and narrow description for science. His ideas have since been criticized, because it has been observed that most of good science does not follow his idealization. The idealization appears to still have great appeal among those, who want to criticize some particular field of science like climate science. As the idealization is not valid, this argumentation presents a fallacy of logic close to the well-known straw man fallacy.
A typical erroneous way of using Popper’s ideas is to require that scientific work should proceed following formally the steps of presenting and testing hypotheses, and in particular through presenting a null hypothesis and proving it wrong. Furthermore it is stated that some results do not present science unless they can be falsified applying this requirement again formally. All these requirements are too narrow and fit poorly the goals of climate science. In climate science there are no new well defined basic hypotheses to prove or disprove. The theories are theories of physics and other basic sciences, such as chemistry. All these theories have already been confirmed extremely well.
Instead of proving or disproving basic theories, the climate science searches for the best possible description of the Earth system. In this work there are no fully correct results, there are only better and worse partial results. The results are not false or correct, they are good or bad, close to the truth or far from it, they are valuable or without merit. The quality of the results of climate science is not two-valued; its value must be measured on a continuous scale of merit.
A real problem of present climate science is that results are expected from it faster than the normal scientific process can produce. The scientific process does not rely on the faultlessness of individual scientific activities; it relies on the self-correcting nature of science. Doing research carefully following all good practices does not guarantee correct results. Science is of creative process searching genuinely new knowledge and that cannot be done without occasional and even frequent errors. The dilemma is created, when decision makers want to use all possible information and when this includes unavoidably also information, whose reliability has not been verified sufficiently by the full scientific process, which may take years to correct some of errors, including sometimes essential errors.
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