Misuses of the complexity argument

In many discussions you encounter the argument "the climate is too complex to be properly understood". But what does it really mean and why do people use it. I think that in many cases it is used to avoid some uncomfortable or difficult question. The more interesting question would be: "What aspects of climate are too complex to be properly understood". Let me give a few examples:

1. Why is it brighter during daytime than during night? Is that complex or simple?

2. Why is it warmer during summer than during winter? Is that complex or simple?

3. Why is the average temperature lower at 5 km altitude than at the surface? Is that complex or simple?

The last question has apparently shown to be too complex for physicists, but maybe it is in fact simple, that we are just too stupid to realize it? Who knows. Maybe the difficulty lies in the fact that the third question posed can under certain circumstances turn almost meaningless. Below I will give two examples of common usage of the complexity argument, one good and one bad.

1. Climatologists claim that the climate is largely determined by the greenhouse effect. They try to prove this hypothesis by running computer simulations and compare them with temperature records of the past, but in reality small temperature variations are too complex to model so the greenhouse hypothesis is still unproven.

2. Nobody has denied the greenhouse effect, but we don't know its future magnitude because climate is so complex. It can be plus 1 or plus 4 or maybe plus 100 degrees or perhaps even -1, who knows, climate is so complex so we shouldn't do anything anyway.

Which one of the above do you think is best?