[mikeash]

I'm not sure if that math makes sense. Most economic activity involves actually doing useful things, not just shuffling numbers around. Obviously there is a segment of economic activity which is, but the vast majority is other stuff.

If you get $2 trillion of economic activity denominated in Bitcoin, that activity is going to use a lot of energy in its own right. The energy used for transferring the Bitcoins around goes on top of that. If the network itself uses 2% of worldwide energy usage, that doesn't leave much for the economic activity it represents.