Unfortunately, evaluating this leaves us with 341.75 Wm-2 = 240 Wm-2, which is (manifestly) not valid—though at least both sides come out on the same order of magnitude, which should suggest that we’re on to something. What’s the problem? In order to diagnose where things are going wrong here, we’ll have to dig more deeply into the energy balance class of models, and start to construct a more realistic model—one which begins to at least approximately get things right.
The basic ZDEBM of the climate is roughly analogous to the simple “calorie balance” model of nutrition—if you consume more calories than you burn each day you will gain weight, and if you burn more calories than you consume you will lose weight. In both cases, while the model in question does indeed capture something accurate about the system in question, the real story is more complicated. In the case of nutrition, we know that not all calories are created equal, and that the source of the calories can make a difference: for instance, consuming only refined carbohydrates can negatively impact insulin resistance, which can affect the body’s metabolic pathways in general, leading to systemic changes that would not have occurred as a result of consuming an equal amount of calories from protein. Analogously, the most simple ZDEBM—in which the Earth and the sun are both featureless points that only absorb and radiate energy—doesn’t capture all the factors that are relevant to temperature variation on Earth.
- Even more strongly, it might be the case that calories in and calories out are not entirely independent of one another. That is, there might be interesting feedback loops at play in constructing an accurate calorie balance: a fact which is obfuscated in this simple presentation. For example, it might be the case that consuming a lot of calories leads to some weight gain, which leads to low self-esteem (as a result of poor body-image), which leads to even more calorie consumption, and so on. This sort of non-linear multi-level feedback mechanism will be treated in detail in Chapter Five, but will be ignored for the time being.