All modelling is based on past experience. The usefulness of a model is the degree to which you can abstract it from that experience.
In the case of the pot of water, you can observe the energy input into the system and combine that with some very generic, simple, and reliable physical models to determine when it will boil.
I'm not claiming that climate science is that simple, of course. My point is that some systems are more easily predicted at a larger scale than a smaller one.
Comments
All modelling is based on past experience. The usefulness of a model is the degree to which you can abstract it from that experience.
In the case of the pot of water, you can observe the energy input into the system and combine that with some very generic, simple, and reliable physical models to determine when it will boil.
I'm not claiming that climate science is that simple, of course. My point is that some systems are more easily predicted at a larger scale than a smaller one.