This is obvious. Why is so difficult to understand that there can still be a deterministic trend even in what can be viewed as a stochastic process. Even though weather is clearly both cyclic and determined by other things, such as solar activity, the levels of greenhouse gasses can, and in sufficiently high concentrations certainly do, have an effect on the weather.

This argument is old and tired. I am quite surprised that you have not heard the appropriate counter argument. In our recent history it is clear that we have had a significant effect on our environment. Over 100 years ago we practically made the buffalo extinct. It was done in a small time frame (10 years or so) using only guns. Forty years ago we saw pollution so bad it was changing the Ph of the rain and lakes were being destroyed. The appropriate history tells us that we can have a major effect large environments. Given that we have had a significant effect on the greenhouse gasses in the atmosphere the question of whether we have the ability to affect the entire planet in a way that affects the weather system is a trivial question. The simple answer is that we do. The question is whether we are affecting the weather systems and if so, the extent to which we are affecting it. After that the discussion continues and addresses what the best course of action is.

I agree that we do not entirely understand the planets weather system but we do not have the luxury of waiting until we fully understand it to make a decision. My guess is that it will be at least hundreds of years before we are able to model weather in a purely deterministic sense. This is not problematic. All of science, pure and applied, deals with incomplete information. We do not have a full understanding of physics, chemistry, biology, economics, psychology and history let we make decisions based on them in every day life. Some of these decisions are made based on necessity, such as economic decisions, and others are made in what might be seen as a more flexible environment such as the choice to pursue a technological innovation. In each situation the choice mechanism is no different we make the choice based on the best information we have on hand. Since greenhouse gas emissions are more costly to decrease in high quantities and over short periods of time we do not have the luxury of waiting until we are all but certain yet alone until we understand the systems perfectly.