Ledgers, Graphics, and Carvings:
This is a series of articles on models. In this series, I am trying to develop a way to build a foundation for non-scientists to feel comfortable about models and their use in scientific investigation.
Doing Science with Models 1.2: In the first entry of this series, I argued that if one considered the types of models used in design and engineering, then we use models all of the time. In fact, when we build or do just about anything, we use some sort of model to get us started. I ended the previous entry of the example of building a simple picnic bench that would hold three, two-hundred-pound men. Not only do the materials need to be of sufficient strength, but the legs of the bench need to be attached in a way that they form a solid and stable foundation. If the bench wobbles and the legs spread apart, then it will be unsafe. If we have experience of some sort, we construct a model from this experience. For example, if we have built or repaired tables and benches we have some ideas of good and bad construction. If we have no direct experience then we can find or ask about plans. These plans might be a schematic, a graphic model of the bench.
For those who do not build benches, but who, say, balance their checkbooks, there are models as well. The forms in a ledger represent models that have proven usable through practice or that have become standard approaches. Information is collected and organized: the check number, the date, the payee, the amount, the purpose and the category of expenditure.
These graphic, tabular, or touchable models are common enough that we develop intuition about their use. Introductory materials to climate models often use the words “mathematical,” “numerical,” and “computational.” These words take us not only away from our intuitive notions of models, but also into subjects that many of us find difficult and obscure. However, in the past couple of decades we have seen the tabular models of checkbook balancing coded as computational products such as Quicken. Design and architecture move to tools such as Computer-assisted Design. Recently, we have seen this combination of the world of digital models and touchable products come full circle with the advent of three-dimensional printing. In three-dimensional printing, solid objects made of plastic and metal are rendered from mathematical descriptions of the objects. I will return to this idea of mathematical descriptions of objects later. The point that I would like to make now is that using computers as tools to represent the real world has in the last two decades become routine. Therefore, in and of itself, the use of computers to make numerical calculations of the real world is common. It might not be as universally intuitive to people as a ledger or a wooden design of a boat, but there is large body of experience that affirms the value of computer-based modeling.
There are a number of steps that need to be taken from here to climate models. So far, I have been talking about models that are in the spirit of a work or a structure used in testing or perfecting a final product. In climate modeling, the final product of the construction is a model. It is the purpose of that model to provide a credible representation of the climate. That representation has a number of attributes. There is the attribute of representing what we have already observed. There is also the attribute of predicting what we will observe, that is, predicting the future. Therefore, the final product of the whole process is the simulation of and the prediction of the climate.
As with many words, there is more than one definition of model in the dictionary. Another relevant definition from my print edition (third) of the American Heritage Dictionary is “A schematic description of a system, theory, or phenomenon that accounts for its known or inferred properties and may be used for further studies of its characteristics.” (American Heritage Dictionary online) This definition is directly descriptive of a climate model. But like those introductions to climate models that I referred to above, it quickly goes to words like “system” and “theory” that are not quite as intuitive as I would like. This is where I will start next time.