There have always been volcanoes and forest fires and methane embedded in various forms. As they perturbed the atmosphere and therefore the climate, the planet's systems reacted to restore the atmospheric balance. These actions/reactions occur over long periods of time, compared to human life, and climate science attempts to understand these forces. There seem to be people who think that even attempting to understand these things cannot work. I don't mean to be dis-respectful, but are you kidding me? We are surrounded every minute of the day by things that no one understood a century ago.
Humans ARE modifying the climate by introducing greenhouse gases by burning fossil fuels. The question is: are we introducing them at a rate and quantity so rapid and large that the planet's systems cannot adapt rapidly enough. This is only of concern to us, btw. The balance that is required is only necessary for our well-being. If the planet cannot adapt rapidly enough, all that will happen is that many humans will suffer and die. The planet will go on, it never needed us and does not need us now. Humans are simply an evolved adaptation to the current natural world. If those conditions change too much and too quickly, we disappear. I speak in hyperbole here, of course, we won't all necessarily die.
So, if we can hone the modelling to the point where we can more or less decide that they predict things (closely enough) to have some confidence in the prediction, then we will know how much money to divert to saving Miami, Bangladesh, New York, etc.
What I don't comprehend is why there is so much objection to doing this research to try and understand climactic change. The starting point seems to be that because some have an axe to grind, they come to the a priori conclusion that not only is the study a waste of time, it is also wrong-headed. How can you know that until you do the research? The objections all sound like ego-protest, some of generic rebellion against ideas that are perceived to be too 1960 ish or too "left" (whatever the f**k that means these days), or anti-business (as if "business" is the end-point). A whole lot of people who don't know much seem to have decided that it's all bunk.
There is also an idea floating around that we can't do anything about it anyway so let's not do anything because there are other things to spend money on. We can't do much about naturally occurring phenomenon, but we can do something about the harm that we have done ourselves, but we have to understand it first. If we understand actions that create harm, then we can change those actions. I understand that some may not want to change, but change might be coming whether you want to or not. The idea that we have better things to spend money is silly. There are always optional ways to spend money, we decide the priorities. We blow tons of cash on NFL gambling, bombing places for discernible long-term benefit, etc., there is no end of things. To single out climate research as too expensive is a laughable idea.