So the question is: if bitcoin replaces US dollar as an international currency, what would look it like today? According to some Google searches, there are 80 trillion dollars in the world. Total Bitcoin supply is 21 million. It means that 1 BTC would be valued around $3.8 million or 277 times more of its current valuation. Currently bitcoin eats around 7.46 GW, so it'll become 2 TW. Current world energy consumption is 157 TW.

So that's a rough estimate upper bound if Bitcoin would become our civilization currency of choice: 1.2% of total energy spent.

Not the end of the world, if you ask me.