So the thread on cars / cycles tripped a switch in my brain - I remembered reading a Maths professors take on UK climate needs (something like covering all of Wales in wind farms).It struck me that I don't have a good feeling for what a sustainable world looks like - what does a city without car addiction look like? What do we do with the space roads now take up?  If we don't farm methane spewing cows what does it do to the need for fresh vegetable delivery? How do we retrofit electric heating and insulation, do supermarkets still work if people don't drive to them.I guess I am looking for first second and third order effects and some kind of model.Any ideas?