To add on to this comment, its ultimately the market that decides how much energy is spent for one bitcoin. Anything else of value will expend the same amount of capital to meet demand. Fracking in oil was a great example because even when the difficulty to acquire this asset increased the market was willing to expend more capital for it as long as it made economical sense. Which is another way of saying, bitcoin has nothing to do with pollution and that responsibility lies solely with the energy sector and how its regulated.