Blockchain: why so energy intensive?

A single Bitcoin transaction currently uses c1,000kWh of electricity, which is 1 million times more than a traditional payment. Hence this 8-page note aims to explain how blockchain works, why it has been so energy intensive in the past, and how the energy multiplier could be reduced to maybe 100 – 1,000 x in a best case future scenario. Thus there could be a role for blockchain in some use cases in the energy transition.