The simplest climate model assumes that all the energy the earth gets from the sun is balanced by the earth radiating it away. The first note gives the details. The second provides guidance on how to build it. The third spends some time analyzing the results. Finally, there's a summary of what all can be learned from this simplest of climate models.
Later, I took a look at expanding the simplest model. It still has the same structure, but now it doesn't require you to know how reflective the clouds are. That had some technical issues, which are discussed in the followup. Still some to pursue, which I will at some point.
The Simplest Meaningful Climate Model
Building the Simplest Climate Model
Analyzing the Simplest Climate Model
Summary of the Simplest Climate Model
Expanding the Simplest Climate Model