According to a recent study published in Nature Sustainability, it takes 17 MJ of electricity to mine one dollar worth of Bitcoin. Compare that to the 5 MJ of energy are required to physically mine one dollar worth of gold. Furthermore, mining one dollar worth of Bitcoin requires more energy than mining not only gold, but also platinum (7 MJ), copper (4 MJ), and rare earth oxides (9 MJ).
See the full article here: https://www.nature.com/articles/s41893-018-0152-7
Another article finds that if Bitcoin continues to grow at rates of other technological advances, it could alone produce enough CO2 emissions to push warming above 2 °C within less than three decades.
That article can be found here: https://www.nature.com/articles/s41558-018-0321-8