In the blogospheric talk about climate change 'model' gets mentioned a lot. Sometimes it's merely descriptive, and often it is perjorative. But it is mostly never really defined. Like or loath them, nobody says just what models are. Except for me, here and now. (And probably a number of other people at other times and places -- but still, few and far between. :-)
'Obviously' a model is a particularly attractive human. Right? I've actually received email at my workplace (a 'modelling branch') from people who were trying to advance the careers of their models, in this sense of model. We don't deal with that kind of model.
'Obviously' a model is to take the original (the Apollo Saturn V rocket that took people to the moon, for example) and duplicate everything about it, but at 1/32 the original size Right? Perhaps. I know people tho like this sort of thing. But again that's not what we mean either if we are discussing climate (or atmosphere, ocean, sea ice, land, glacier, ...) models.
For my purposes, a model is an idealized, and/or simplified, representation of the real world. When we are interested in something as big and complex as climate, or even just the Arctic sea ice pack, we really can't cope with the whole thing in all of its glorious complexity. We have to simplify the reality somehow. That simplification is the model.
In this sense of 'model', models are everywhere. We use a model for human behavior when we decide what somebody else means when they raise their hand in a certain way. (is it open hand, or a fist? did they just say 'hello', or 'I'm going to kill you'. and so on) Weather has also been modelled by using 'dishpans' -- Raymond Hide and David Fultz being two of the best examples of people taking this approach*.
In working with satellite observations, there are different models involved, about the structure of the atmosphere and surface of the earth, how they vary in space and time, and what exactly your satellite observed. In pondering how climate will change if we do certain things (what things exactly? oops, another model) to the earth's atmosphere and surface, we use different sorts of models.
I'll take up a bit of this line tomorrow.
* The (scientific) world is a very small place -- David Fultz was my professor for general meteorology, general oceanography, and synoptic meteorology. Ray Hide was advisor to two of my coworkers, and I've corresponded with him about an idea of mine that I'll be discussing in a bit on this blog. While the world at large might be within 6 degrees of separation, I'm thinking that science is more like 2.