Jonathan Lawhead

“ Such a narrow focus is a double-edged sword; it makes EMICs far easier to work with than their monstrously complicated big brothers, but it also limits the class of predictions that we can reasonably expect to get out of applying them. If we’re going to get as complete a picture of the patterns underlying the time-evolution of the Earth’s climate as possible, then we’ll need as many tools as possible at our disposal: low-level energy balance models, EMICs, and high-level holistic models. ”

“ We’ve already noted that the atmosphere isn’t entirely transparent from the perspective of the Earth: it absorbs some (but not all) of the outgoing radiation. Let us add a term to our model to reflect the opacity of absorbing surfaces. Call this term γ. A surface that is totally opaque has γ = 1 (it absorbs all the energy that actually reaches it) , and a surface that is totally transparent to incoming radiation has γ = 0. Note that this term is independent of α: a surface’s opacity only comes into play with regard to the energy that isn’t just reflected outright. ”

“ While the model we have just constructed is a working model, the like of which one might encounter in an introductory course on climate science, it still represents only a tiny slice of the myriad of processes which underlie the Earth’s climate. We went through the extended derivation of the last section for two reasons: first, to provide some structure to the introduction of central concepts in climate science (e.g. albedo, the greenhouse effect, opacity) and second, to demonstrate that even the simplest models of the Earth’s climate are incredibly complicated. ”

“ The greatest triumph of the scientific revolution was, arguably, the advent of the kind of experimental method that still underlies most science today: the fundamental insight that we could get a better handle on the natural world by manipulating it through experiment was, to a large degree, the most important conceptual leap of the era. ”

“ The moral of the science’s success in the 20th century is that the mainstream scientists were right and the vitalists were wrong: living things (a fortiori, brains, democracies, economies) are really nothing over and above the sum of their parts—there is no vital spark, and no ghost in the machine, and no invisible hand. The progress of science seems to have born this out, and in a sense it has: in looking for (say) living things to behave in ways that were not determined by the behavior of their cells and genes, vitalists were chasing ghosts. ”

“ How much solar energy does the Earth receive? Well, just however much of the sun’s energy actually reaches as far as the Earth multiplied by the size of the area of the Earth that the sun is actually shining on. ”

“ Since our ultimate goal is to focus our discussion in on anthropogenic climate change, we can limit our attention to those factors that might play a significant role in understanding that problem. To begin, it might be helpful to get a very basic picture of how the Earth’s climate works, with particular attention to temperature, since this is a feature of the climate that will be of great interest to us as we proceed. ”

“ Rather than acting like a greenhouse (which suppresses convection) , the presence of a heterogeneous atmosphere on Earth acts something like an array of very small one-way mirrors, permitting virtually all incoming radiation to pass relatively unimpeded, but absorbing (and later re-radiating) much of the energy emitted by the planet itself. ”

“ The logic of energy balance models is sound, and more sophisticated energy balance models add more detail to account for some of the factors we just enumerated; with every addition of detail, the model becomes capable of generating more accurate predictions but also becomes more difficult to work with. For instance, we might move from the ZDEBM to a one-dimensional energy balance model, modeling the Earth not as a point but as a line, and expressing the parameters of the model (like albedo) not as single terms, but as differential equations whose value depends on where we are on the line. ”

“ To begin, we should note that as some skeptics [14] of anthropogenic climate change have pointed out, the term “greenhouse effect” is somewhat misleading: the mechanics of the effect bear only a passing resemblance to the mechanics of man-made greenhouses. Artificial greenhouses are kept warmer than the ambient environment primarily through a suppression of convection: that is, the glass in the greenhouse prevents warm air—which is less dense than cold air, and so will tend to rise above it—from rising away from ground level, and thus keeps conditions warmer than they would be otherwise. ”

“ It was Galileo’s genius to realize that by reducing a system of interest to its simplest form—by controlling the system to hold fixed as many variables as possible—patterns that might be obscured by the chaos and confusion of the unmodified natural world would become more apparent. ”

“ While quantum mechanics was busy overthrowing other pillars of classical physics, it seemed to only reinforce this one: the whole is nothing more than the sum of its parts. While the behavior of that sum may be difficult (or even impossible) to predict sometimes just by looking at the parts, there’s nothing fundamentally new to be learned by looking at systems; any higher-level scientific laws are just special cases, course-grainings, or simplifications of the story that fundamental physics has to tell. ”

“ Beyond RC models, the field becomes increasingly differentiated and heterogeneous—in the last 30 years in particular, a large number of so-called “Earth models of intermediate complexity” (EMIC) have sprung up in the literature. It is impossible to characterize these models in any general way, as each is constructed for a very particular purpose—to model some very specific aspect of the global climate based on a parameterization that fixes other potentially relevant factors as (more or less) constant. ”

“ There are clear cases that fall into one or another discipline—the question of how likely it is that it will rain tomorrow is clearly a question for weather forecasting, while the question of how the Earth’s changing axis of rotation contributes to ice ages is clearly a question for climatology—but many questions will be of interest to both disciplines, and there is bound to be significant overlap in both topic and method. ”

“ With an atmosphere to act as a heat reservoir, though, temporary removal of the active energy source doesn’t result in such an immediate and drastic temperature drop. During the Earth’s night, energy absorbed by the atmosphere during the day is slowly re-released, keeping surface temperatures more stable. A similar effect explains why land near large bodies of water (oceans or very large lakes) tends to have a more temperate climate than land that is isolated from water ”

“ For now, we will set this question aside and focus on climate science as it is practiced. As a general rule of thumb, weather forecasting is concerned with predicting particular events, and climatology is concerned with predicting trends. This definition is good enough for our purposes, at least for now.
4.1.1 Basic Energy Balance Models
What, then, are the patterns of interest to climate scientists? In general, climate scientists are interested in predicting the long-term behavior of the Earth’s atmosphere (as well as the systems that are tightly coupled to the atmosphere) . ”

“ Basic RC models will treat the planet not just as a set of “lamps” which absorb and emit radiation, but rather will include enough detail to model the transfer of energy via convection—the movement of air—as well. We can think of RC models as presenting the Earth as a set of connected boxes of various sizes containing gas of various temperatures. ”

“ I proposed the concept of dynamical complexity as best capturing the aspects of the varied proxy concepts we considered that are most relevant to scientists seeking to understand active, dynamical complex systems in the natural world (as opposed to, say, those interested in studying aspects of abstract signals) , and argued effective complexity can plausibly be taken as a physical interpretation of the existing mathematical framework of effective complexity. ”

“ The last major stronghold for this view—life—was dealt a critical blow by the advent of molecular biology, though: the discovery of genetic molecules showed that living things were not anomalous, sui generis systems, but rather were just as dependent on the coordinated action of simpler constituents as any physical system. By the middle of the 20th century, vitalism had fallen far out of favor, and most mainstream scientists and philosophers held at least a vaguely reductionistic view of the world. ”

“ Rejecting the notion that interesting facts about cognition are exhausted by interesting facts about neuronal firings need not entail embracing the notion that cognitive facts float free of physics and chemistry; rather, it just entails a recognition that neural networks (and the organisms that have them) are embedded in active environments that contribute to their states just as much as the behavior of the network’s (proper) parts do, and that the decompositionist assumption that an understanding of the parts entails an understanding of the whole need not hold in all cases. ”

“ Since they are concerned only with possible anthropogenic influences on the climate system, they express radiative forcing values in terms of their deviation from pre-Industrial levels. In other words, their values for the amount of energy reaching certain points on the Earth “subtract out” the influence of factors that they have good reason to think are unrelated to human intervention on the climate. ”

“ A system’s dynamical complexity, recall, is a fact about the pattern-richness of the system’s location in the configuration space defined by fundamental physics. Equivalently, we can think of it as being a fact about how many predictively useful ways the system can be carved up. ”

“ The strongest adherents of computational neuroscience argue that not only do mental states depend on brain states, but that (as a methodological dictum) we ought to focus our scientific efforts on mapping neuronal firings only. That is, it’s not just necessary to understand the brain in order to get a grip on psychology—understanding how neurons work just is understanding psychology. ”

“ While it seems intuitively apparent that more sophisticated models should be better models, it is also the case that more sophisticated models generally leave more room for failure, either as a result of measurement error, because the model accounts for only half of an important feedback loop, or for some other reason. ”

“ The relationship between the energy change of a given molecule [20] and an electromagnetic wave with wavelength λ is:
where is the reduced Planck constant () , so larger energy transitions correspond to shorter wavelengths. When is positive, a photon is absorbed by the molecule; when is negative, a photon is emitted by the molecule. ”

“ These are incredibly deep questions—they represent some of the most difficult practical challenges that working scientists in any discipline face in designing their models—and giving a general answer to them is beyond the scope of our project here. Still, it is worth our time to briefly examine the plethora of climate models that have sprung up in the last few decades, and to think about the conceptual underpinnings of this highly diverse collection of scientific tools. ”

“ A similar mechanism is at work when you leave your car parked in the sun on a warm day: the interior heats up, but because the cabin is air-tight (at least on the timescales of interest to you during your trip to the shopping mall or grocery store) , the warmer air inside the car and the cooler air outside the car cannot circulate, so the temperature increase can build up over time. ”