[crygin]

In addition to the sibling comment's point that externalities of energy production are unevenly distributed, the difference between an old machine and a new machine is that in the manufacture of the old machine the energy/pollution/labor have already long since been expended, and the amortization of that expenditure across more years of use is likely to compete well against even a very efficient newly manufactured piece of equipment. This is most dramatic in e.g. the purchase of cars, where it's typically more environmentally friendly to drive an older, even significantly less efficient car, than to purchase a new car.