https://motherboard.vice.com/en_us/article/a34gjb/bitcoin-mining-more-energy-intensive-wasteful-than-gold-mining

As technical roadblocks continue to hamper Bitcoin’s use as a functional currency, many have taken to defining it as digital gold. But if Bitcoin were to replace gold as a commonly accepted store of wealth, a recent comparison of Bitcoin mining and gold mining suggests that it would be bad for the planet, environmentally speaking.

Even though they’re not identical activities—bear with me on this point—according to blockchain consultant Alex de Vries at Digiconomist, Bitcoin mining is at least 3.25 times more energy-intensive than gold mining, per dollar mined. That’s if all Bitcoin mining were to use the most efficient machines—Bitcoin mining may be closer to 6.91 times more energy-intensive under the more pessimistic assumption that many Bitcoin miners are running old (and less efficient) equipment.