In an unfinished project, I have tried to simplify Stern’s basic idea into a simple diagram along the lines of Alfred Marshall’s supply and demand curves. I replace the P & Q axis with “cost” and “temperature change”. I replace the S & D curves with “Climate change costs” and “Policy Costs” curve. The optimum response is to minimize the combined costs. According to Stern, this lay at constraining CO2 to around 550ppm.

http://manicbeancounter.com/2011/02/11/climate-change-policy-in-perspective-%E2%80%93-part-1-of-4/
Like with most of these diagrams in economics, you can consider various different scenarios, and look at the consequences of allowing for uncertainties, discount rates, speed of climate change, along with new information. On the policy costs, the impact of a small country acting alone, or globally having ineffective policies can be demonstrated.