Ian, you're right, it is complicated. Climate is complicated. The atmosphere is unimaginably large, and there are so many different things which affect it, including the state of the ocean, which has it's own set of complex mechanisms. It's this very complexity which leads to such varying positions. No one, not even scientists, can claim to understand every part of the climate interactions. All they can do is study and model them, and get close approximations.

You are right that the Earth's core is gradually cooling, but the rate of cooling is so slow as to be insignificant over the period since the rise of homo sapiens. The same is true of most natural sources of greenhouse gases, such as volcanoes and earthquakes. These have always been there, and at approximately the same levels, so they can be treated as a constant. The biggest variable currently is mankind. We are releasing millions of tons of greenhouse gases into the atmosphere every year, over and above the naturally occurring gases. While there is still a lot of argument over just how much we are affecting the system, it would be foolish to believe that we are not having any effects at all.

As for your taxes, sorry, I have no good advice for you, other than to monitor the government offices responsible for spending those tax dollars and trying to make sure they are doing what they're supposed to be doing. Though in this day and age that kind of thing just might get you arrested.

As an aside, I remember reading somewhere (and it's too long past my bedtime for me to try to find it now) that climate models which have been run tend to match historical climate data from as far back as they can get it right up until the start of the Industrial Age, at which point the models start diverging, predicting consistently lower global temperatures than are being found. Just one more piece of information to consider.