the one main factor is population.
The production of food. think about it. Go to the store and buy a simple box of cereal.
Now look at how it got there.
Fuel to plant the seed to grow the grain. Fuel to run the manufacturing process to make the grain into a yummy tasting cereal.
Fuel to make the box to store the cereal plus the loss of a tree.
Fuel to move the cereal from the fab to the store.
Fuel for you to go and buy the cereal.
all that just so you do not have to wake up a 5 am and harvest your own food.
Farmer is not so dumb now.
