I wouldn't call this fudging. It's just easier to see the effect when the Y axis starts at the low point of the line, rather than at 0. Especially when you co

I wouldn't call this fudging. It's just easier to see the effect when the Y axis starts at the low point of the line, rather than at 0. Especially when you consider that the atmosphere always contains a baseline level of C02, and we wouldn't want it otherwise; it protects us from a significant chunk of the UV spectrum. This choice could actually be seen as less arbitrary than starting at zero.