Given an Earth-like planet with arbitrary terrain, how can I create a simple climate simulator that can output parameters such as humidity and temperature, so that I can assign biomes to areas of land?

My knowledge of climate modelling approaches zero, so to take a step back: is such a simple model even possible (i.e. one accessible to hobbyists), if so are there examples, if not where can I get started?

My motivation is that, it seems to me that a lot of fictional worlds were created without applying climate models. Their creators often apply a very simple model (e.g. things are wet near the seas and get drier inland), most don't even try to determine things like rain shadows. I thought that we could improve a lot on this situation by applying some simple climate science principles. With this motivation in mind, I'm aiming more for verisimilitude than rigor.

This recent story about some climate scientists modelling the climate of Middle Earth is in line with what I'm aiming for, although I read that they used HadCM3L which doesn't seem like something accessible to laymen.

To show what I've tried so far, I've done a bit of reading and come up with the following. It's been difficult for me because I'm a novice, and also a lot of available material seems to be focused on the climate change issue. Perhaps Paleoclimatology is more relevant? I have no idea.

  • Prevailing winds, caused by Hadley cells, and affect cloud movement and creates surface currents and gyres
  • Deep ocean currents, caused by salt and temperature differences near the poles and circulates globally, which combines with the gyres to form warm current flows
  • Air masses, whose temperature and humidity are determined by whether they're over land or sea, create weather fronts and lots of precipitation between them
  • Mountain ranges that, in the presence of humidity-carrying winds, cause orthographic lift and rain shadows afterwards

I have no idea whether this is on the right track, and even if so, how far the rabbit hole goes (e.g. do I have to worry about the influence of moons/tides? What about effects of vegetation like forests?)