R.S. Lindzen, 2102: Climate physics, feedbacks, and reductionism (and when does reductionism go too far?). Eur. Phys. J. Plus (2012) 127: 52 DOI 10.1140/epjp/i2012-12052-8.
The introduction reads (there is no abstract) [highlight added]
The public perception of the climate problem is somewhat schizophrenic. On the one hand, the problem is perceived to be so complex that it cannot be approached without massive computer programs. On the other hand, the physics is claimed to be so basic that the dire conclusions commonly presented are considered to be self-evident. Consistent with this situation, climate has become a field where there is a distinct separation of theory and modeling. Commonly, in traditional areas like fluid mechanics, theory provides useful constraints and tests when applied to modeling results. This has been notably absent in current work on climate. In principle, climate modeling should be closely associated with basic physical theory. In practice, it has come to consist in the almost blind use of obviously inadequate models.
In this paper, I would like to sketch some examples of potentially useful interaction with specific reference to the issue of climate sensitivity. It should be noted that the above situation is not strictly the fault of modelers. Theory, itself, has been increasingly idealized and esoteric with little attempt at real interaction. Also, theory in atmospheric and oceanic dynamics consists in conceptual frameworks that are generally not mathematically rigorous. Perhaps, we should refer to it as physical or conceptual reasoning instead. As we shall see, when reductionism goes beyond the constraints imposed by these frameworks, it is probably going too far though reductionism remains an essential tool of analysis.
The concluding remarks read
This paper considers approaches to estimating climate sensitivity involving the basic physics of the feedback processes rather than attempting to estimate climate sensitivity from time series of temperature. The latter have to assume a perfect knowledge of all sources of climate variability —something generally absent. The results of a variety of independent approaches all point to relatively low sensitivities. We also note that when climate change is due to regional and seasonal forcing, the concept of one dimensional climate sensitivity may, in fact, be inappropriate. Finally, it should be noted that I have not followed the common practice of considering the feedback factor to be the sum of separate feedback factors from water vapor, clouds, etc. The reason for this is that these feedback factors are not really independent. For example, in fig. 2, we refer to a characteristic emission level that is one optical depth into the atmosphere. For regions with upper level cirrus, this level is strongly related to the cloud optical depth (in the infrared), while for cloud-free regions the level is determined by water vapor. However, as shown by Rondanelli and Lindzen , and Horvath and Soden , the area covered by upper level cirrus is both highly variable and temperature dependent. The water vapor feedback is dependent not only on changes in water vapor but also on the area of cloud-free regions. It, therefore, cannot readily be disentangled from the cloud feedback.
One interesting statement in the paper is that, with respect to regional climate features,
“……current models do not simulate the PDO [Pacific Decadal Oscillation]. We are currently beginning such a study.”
The entire article is an important new contribution to the climate science discussion by a well-respected colleague. I recommend reading the entire article.
My one substantive comment is the use of the terminology “climate sensitivity“. I recognize that so much of the literature is focusing on the response of the global, annual averaged surface temperature to an imposed global averaged forcing (such as the radiative effect of added CO2) and calling this “climate sensitivity“. However, this is but a very small part of true climate sensitivity. While I completely agree with Dick that there is a fundamental problem with “one-dimensional thinking” as he discussed in section 4 of his paper, it is an even higher dimensional (and more complex) issue than presented in the paper.
As I have often presented on my weblog, the climate system can be schematically illustrated below from NRC (2005).
The real world climate sensitivity is the influence of natural and human climate forcings on each of the components of the climate system. Research is only just beginning to examine this issue, which needs to be completed using the bottom-up, contextual vulnerability approach that we discuss in our paper
Pielke Sr., R.A., R. Wilby, D. Niyogi, F. Hossain, K. Dairuku, J. Adegoke, G. Kallos, T. Seastedt, and K. Suding, 2011: Dealing with complexity and extreme events using a bottom-up, resource-based vulnerability perspective. AGU Monograph on Complexity and Extreme Events in Geosciences, in press.