...this is going just too hypothetical... I was thinking of the Apollo 13 movie - have you seen it? There is a scene where the NASA engineers need to pull an electronical trick without crossing a certain volts (or watts?) threshold. I was just moulding a similar thought experiment.

This is what I wonder: if you take away all of the advantages of the fossil fuel society since the Industrial Revolution - you end up in a world that would probably resemble the Amish communities quite well. I believe that the Amish are practically self-sustainable - I still have not confirmed whether they truly are, but let's assume just that.

So. Boundary Condition:
1) Self-sustainable

Parameters:

1. Ecological Foot Print of X
   
2. Carbon emissions of Y
   
3. Others

You take that as your basic structure, then add chunks of our modern society into the Amish "model" and track at what point self-sustainable turns into unsustainable. It's merely a thought experiment of finding the breaking point of sustainable communities.

By taking the modern world as starting point at the premise of being unsustainable, you'll have to take stuff away to get to your sustainable society - eg, you model backward. I would like to know what stuff of the modern world can be slotted into a working sustainable model - modelling forward. That's "working from scratch".

I just realise that the phrases forward and backward modelling may be just typical earth scientist expressions... I've never seen it in other literature. Anyone here to contradict me?