Environmental decision making in everyday life

I wrote this when I was in an exceptionally nerdy mood.

Say you were driving someone to the airport, and once arriving there they realize they forgot something. Of course if it was a passport or something to that effect you'd have to go back anyway, but what if it was something like a jacket? You'd then have the option to

A) drive back home to pick up the jacket, or
B) buy a new jacket at the airport.

If your goal is to make the choice that is most environmentally friendly, which one would you make? How do you decide which one to pick? While driving back and to the airport again intuitively sounds like the worst option, let's reconsider the costs and impacts of both options.

• What is the cost of driving to and from the airport? For this case let's say it costs $20.
• What is the cost of buying a new jacket? That is unknown until you actually buy the jacket, which you can only do after you've already decided to buy it, so let's estimate it. I'll say about $100. Now we convert this into a percentage value so that we can relate it to the badness impact scale.
  
• what are the impacts of buying a new jacket? This is where it gets complicated. We have to consider the social impacts of buying something made out of sweatshops, the environmental impacts of producing man-made materials and all that energy and water used up in growing the cotton, the distance the materials were transported, all the chemicals used in bleaching, dying, etc. There's no way to really calculate this objectively, so let's give it a badness percentage scale, 100% being the worst a person can do, and 0% being the best. That will have to remain entirely a matter of opinion. I'm going to estimate that buying a new jacket is 50% bad.
  
• what are the impacts of buying x litres of gas? I'm going to say about 25L estimated from the cost, but, as the example above, I'll have to consider abstract badness values for what I think is the "badness" of using up 25L of gas. Things to consider? The economy, war, using up non-renewable resources, contributing to global warning and all manner of diseases, etc. For me, I will give this a badness scale of 45%.

so let's say your decision, x, goes like this:

x = [cost(A) - cost(B)] / [impact(A) - impact(B)]

A must have a different value than B, obviously. if c(A)=c(B), use impact to make the decision, and vice versa.

so if x > 1, you go with option A
and if x < 1 you go with option B
and if x = 1, use the time spent to make the decision. How long would it take to drive back home, how long would it take to buy a new jacket? Go with the least time wasted.

so in this case,

x = (100-20)/(50-45) = 80/5 = 16
x > 1, therefore I drive back home to get the jacket.

I think a similar decision making process can be used to decide whether to eat local or organic.