Market cap is a bad metric. A better one would be transactions. According to https://digiconomist.net/bitcoin-energy-consumption https://digiconomist.net/bitco

Market cap is a bad metric. A better one would be transactions. According to https://digiconomist.net/bitcoin-energy-consumption https://digiconomist.net/bitcoin-energy-consumption bitcoin is on track to consume 19 TWh this year. That puts it at .1% of the global power consumption already NASDAQ does 10 million trades a day, roughly. So if bitcoin scales to just handle NASDAQ alone it would consume ~850 TWh/year, which is 3.5% of the total world's electricity generation (to say nothing of Visa's 150 million transactions a day) The reason bitcoin isn't currently an enormous threat is because it's basically barely used by comparison. 300,000 trades/day is a tiny number in the world of financial transactions.